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EFFECT OF MIXING GROWING MEDIUM AMENDMENTS

 

 

Horticulture Workshops

Plant Propagation

Soil and Soilless Growing Media

Simple Soil and Water Testing

 

 

David Wm. Reed

Department of Horticultural Sciences

Texas A&M University

 

 

 

 

 

 

 

University of Veracruz

Xalapa

 

 

Summer 2007


Table of Contents

 

 

 

 

Topics                                                                                                             Page

 

Asexual or Vegetative Propagation

Cuttings                                                                                                           3

Rooting Hormones                                                                                          5

Propagating Variegated Plants (Chimeras)                                                   6

Layering                                                                                                          8

Grafting and Budding                                                                                   11

Division                                                                                                         14

Tissue Culture                                                                                               15

 

Sexual or Seed Propatation20

Seed Dormancy                                                                                             22

Scarification                                                                                                  24

 

Potting Soil for Containers

Soil                                                                                                                 27

Amendments                                                                                                 29

How to make Soilless Growing Medium Mixes                                          33

 

Simple Soil and Water Testing

Porosity of Soil and Growing Media                                                            36

Aeration and Water Holding Capacity of Soil and Growing Media           37

EC and pH of Soil and Soilless Growing Media                                          39

EC, pH and Alkalinity of Irrigation Water                                                  43

 


Plant Propagation

David Wm. Reed

Professor of Horticulture

Department of Horticultural Sciences

Texas A&M University

 

Asexual or Vegetative Propagation

 

Asexual (or vegetative) propagation is the non-sexual reproduction or propagation (by cuttings,    layering, division, grafting or budding) of a new plant from vegetative organs (stem, root, leaf).  This is opposed to sexual propagation (union of gametes) from the reproductive organ, the flower, and resultant fruits and seeds.

 

Asexual propagation may lead to the formation of a clone, which is defined as a group of plants that were all derived from the same parent and are propagated solely by asexual (vegetative) means, such as cuttings, layering, division, grafting or budding.  An example of a clone would be a group of plants that were all propagated as cuttings from the same plant.  Many horticultural cultivars were propagated from a single seedling, from a single mutation that was found as a branch on a plant, or from a mutation artificially produced by plant breeders or geneticist.  Since all subsequent plants were propagated from this single seedling or mutated organ, the entire cultivar is a clone.  Examples are: 'Bartlett' pear, 'Queen Elizabeth' rose, and 'Golden Hahnii' Sansevieria.  Some clones originated centuries ago.  For example, 'Bartlett' pear originated in 1770.

 

Tissue culture (often called micropropagation) is a special type of asexual propagation where a very small piece of tissue (shoot apex, leaf section, etc.) is excised (cut-out) and placed in sterile, aseptic culture in a test tube or Petri dish containing a special culture medium.  The culture medium contains the proper mixture of nutrients, sugars, vitamins and hormones, which causes the plant part to grow at very rapid rates to produce new plantlets.  It has been estimated that one chrysanthemum apex placed in tissue culture could produce up to 1,000,000 new plantlets in one year.  Thus, tissue culture is used for rapid multiplication of plants.  A very specialized laboratory is required for tissue culture.

 


 

Propagation by Cuttings

BACKGROUND

A cutting, sometimes called a propagule, is a portion of a stem, root or leaf taken from a parent plant that, when placed under favorable environmental conditions, regenerates adventitious roots and/or adventitious shoots.  This produces a new independent plant identical to (or a clone of) the parent.

 

Cuttings are classified based on the plant part from which they are taken (stem, root or leaf) and their state of growth (herbaceous, hardwood, etc.).  Stem cuttings must form adventitious roots (they already possess shoots), root cuttings must form adventitious shoots (they already possess roots) and leaf cuttings must form both adventitious roots and adventitious shoots (they possess neither).

 

When stem and leaf cuttings are removed from the parent plant they are cut-off from their source of water.  Provisions must be made to prevent the continued loss of water or many cuttings will desiccate (dry out) and eventually die.  Most methods to prevent water loss of cuttings involve decreasing light and temperature, and increasing the relative humidity around the cutting.  For many plants this is accomplished by merely placing them in a shaded cool area away from direct sun or spraying the foliage with water several times per day.  This usually is sufficient for deciduous hardwood cuttings and for succulent plants.  Many small businesses and homeowners construct a rooting frame or humidity chamber, which is any box, pot, bench or tray enclosed by a polyethylene (plastic) tent in which the cuttings are placed.  The polyethylene lets in needed light (do not place in direct sun or overheating occurs from the greenhouse effect) and keeps the humidity high around the cuttings.  Most commercial operations utilize an intermittent mist system in which a very fine mist of water is automatically and periodically (intermittently) sprayed over the cuttings to decrease both water loss and heat build-up.  The use of intermittent mist allows the propagation of many plant species that otherwise are very difficult or impossible to propagate, especially leafy herbaceous and softwood cuttings.

 

mist and humidity chamber

Commercial intermittent mist system and home-made humidity chamber used for propagation of cuttings to prevent desiccation (drying out).


 

TYPES OF CUTTINGS

LEAF CUTTINGS - must form both adventitious
                                 shoots and roots (except leaf bud). 

a) leaf bud

b) leaf petiole

c) leaf blade

d) leaf section

STEM CUTTINGS - must form adventitious roots 

a) hardwood

b) semi-hardwood 

c) soft or greenwood 

d) herbaceous 

hardwood 

       semi-hardwood,
softwood 
or herbaceous

e) cane
    leafless stem 

f) rhizome 
    underground stem

cane 
                   rhizome 

g) tuber
    underground storage
    stem

tuber


ROOT CUTTINGS
must form adventitious shoots

root section

tuberous root

 


Rooting Hormones

BACKGROUND

The cuttings of many plant species will form adventitious roots readily when placed under the appropriate environmental conditions.  However, the cuttings of some plant species are very difficult if not impossible to root.  Many of these difficult-to-root plant species can be encouraged to form roots with the use of certain growth regulators, which are sold commercially as "rooting hormones".  The commercially available "rooting hormones", their components and properties are listed in the table below.  These "rooting hormones" or root-inducing growth regulators are composed almost exclusively of auxins.

 

The most effective and commonly used auxin is IBA (indolebutyric acid).  NAA (naphthaleneacetic acid) also is used frequently, but usually is less effective than IBA.  2,4-D (2,4-dichlorophenoxyacetic acid) is infrequently used.  2,4-D acts as an herbicide at high concentration, so it must be used carefully.  Many other compounds have auxin-like root-inducing properties, but commercially are used less frequently.  IAA (indoleacetic acid), the only naturally occurring auxin, is very seldom used due to its instability, both in solutions and once absorbed by the plant.

 

"Rooting hormones" will not force a plant to root that lacks the inherent capacity (either genetic or physiological) to form adventitious roots.  However, for many plants auxin may: 1) increase the % rooting of cuttings, 2) decrease rooting time, 3) increase the number of roots formed per cutting, 4) increase the quality of roots produced, and 5) increase the uniformity of rooting.  For of these reasons "rooting hormones"  are used routinely by plant propagators.

 

Commercially Rooting Hormones (auxins)

Commercial

Name

Auxin

is the Active Ingredient

Concentration (ppm)

Formulation

Hormodin #1

IBA

1000

talc powder

Hormodin #2

IBA

3000

talc powder

Hormodin #3

IBA

8000

talc powder

Rootone

IBA 
M-NAA 
M-NAM 
NAM

570 
330 
130 
670

talc powder

Jiffy-Grow

IBA 
NAA

500 
500

solution

Quick-Dip 
(home-made)

IBA (usually) 
in 50% alcohol

500-10,000

solution


Propagating variegated Plants (chimeras)

 

CHIMERA (ki mer' a)

 

Chimera - a plant or plant part composed of genetically different layers.

The most common example is a "variegated" plant where different regions or layers of the leaf are yellow or white due to no chlorophyll development, i.e. these are chlorophyll mutants. 

GROWING POINT OR APEX –composed of  3 different layers called L-I, L-II and L-III. 

Layer

Gives rise to:

L-I

epidermis of all organs; 
monocot leaves - L-I  contributes to the outermost region of the leaf mesophyll giving 
                          rise to a strip along the leaf margin. 
dicot leaves - L-I usually gives rise to only the colorless epidermis, thus cannot be seen; 
                     sometimes L-I gives rise to small islands of tissue along the margin.

L-II

stem and roots: outer and inner cortex and some of vascular cylinder 
leaves: mesophyll in outer region of leaf

L-III

stem and roots: inner cortex, vascular cylinder and pith 
leaves: mesophyll in central region of leaf 

 

LOCATION OF LAYERS IN A TYPICAL DICOT

 


NEVER PROPAGATE CHIMERAS BY LEAF CUTTINGS - WHY?
(for the same reasons - never use root cuttings)
(Modified from: R.A.E. Tilney-Bassett. 1986. Plant Chimeras. Edward Arnold Ltd.,
Balt., MD)

 

VARIEGATED LEAF PATTERNS OF CHIMERAS

The leaves below demonstrate two types of variegated Elaeagnus.  The cultivar on the left is an L-II chimera (i.e. GWG), and the cultivar on the right is an L-III chimera (i.e. GGW).  These are chimeras where the yellow or albino regions cannot make chlorophyll. A cross-section of the leaf shows the regions of albino cells in the mesophyll.  The different shades of green and yellow are determined by the depth of the cell layers..

 

 

ADVENTITIOUS SHOOT FORMATION ON LEAF CUTTINGS OF CHIMERAS

If you take leaf cuttings from variegated plants, such as these variegated Peperomia (GWG), the plantlets that form are never true-to-type to the parent variegation.  The reason is simple.  The adventitious shoots that form will have the properties of the region of the leaf from which they regenerate.  The same would happen with a root cutting.  For this reason, chimeras are never propagated true-to-type by cutting types or methods that require adventitious shoot formation.

 


Propagation by Layering

 

BACKGROUND

Layering or layerage is a propagation technique where roots are induced to be formed on a stem prior to detachment from the parent plant.  This is contrasted to cuttings, where roots are formed after detachment from the parent plant.  Layering is a common process in nature for many plants, such as blackberry, ajuga, and strawberry, which results in their self-propagation.  Horticulturists have taken advantage of this naturally occurring process and have used it artificially for the propagation of many plant species.  Layering is much less of a "shock" to the plant than taking cuttings, and a nearly salable plant (relatively large plant with shoots plus roots) is detached from the parent plant.

 

The basic principle underlying layering is disruption of the downward translocation of photosynthates (sugars), hormones, and other metabolites by either girdling, ringing, notching, tying or bending of stems, but at the same time minimizing any disruption of upward translocation of water, thus allowing the top section to continue normal functioning (photosynthesis, metabolism) during the rooting process.  Ideally, one would like maximum disruption of downward flow in the phloem, while allowing minimum disruption of upward flow in the xylem.  To achieve this "ideal", one would like to cut as much of the phloem , but as little of the xylem as possible.  The type of cut is dictated by the internal anatomy of the stem.  Woody dicots have rings of vascular tissue, and the ring of phloem can be removed by removing the layer of bark.  Monocots have scattered vascular bundles, hence, the stem is partially slit to severe some of the vascular bundles.

 

How to Make An Air Layer

 

Monocot Air Layering

1)   Six to twelve inches (15-30 cm) from the stem tip, depending on the plant, make a diagonal (30-45o) cut or slit through a node and 1/3 the way through the stem.  Place a toothpick, match stick or bamboo strip across the slit to hold it open.

 

2)   Wrap the area with moist, but not soggy, coarse unshreaded sphagnum peat moss to form a ball approximately 7-10 cm (3-4") in diameter.

 

3)   Wrap and completely enclose the sphagnum peat moss ball with a polyethylene (plastic) sheet.  Tie-off the ends of the plastic with twist-ties (or rubber bands, or tape).  Make sure no shreds of sphagnum extend from the polyethylene wrapping or it will wick-out all of the water.

 

4)   The layered area may be covered with aluminum foil to decrease light and temperature build-up (i.e. greenhouse effect).

 

5)   Bamboo stakes may be attached as splints along the stems across the layer for added support.

 

6)   When a fair number of roots are visible in the sphagnum and against the polyethylene, cut the layer off from the parent plant just below the peat moss ball, and remove the foil and plastic.  Pot the layer in a suitable medium and pot, then water well and place in a shaded area for a few days.

 

Dicot/Gymnosperm Air Layering

1)      Six to twelve inches (15-30 cm) from the tip of the stem (depending on the plant species) make 2 ringing (girdling) cuts 1/2-1" (1-3 cm) apart.  Connect the 2 cuts with a longitudinal slit and remove the cylinder of bark.  Scrape the exposed surface of the stem to remove all adhering phloem and cambium.

2)   Same as Steps 2-6 for monocot

ANATOMICAL BASIS FOR THE TYPE CUTS USED IN LAYERING

Woody Dicots and Gymnosperms

A ring of bark is removed from around the stem.  The phloem and cambium are attached to the inside of the bark, so when the bark is removed the phloem is also removed.  This leaves the central cylinder of xylem and upward water flow unaffected.

 

Monocots
Monocots have scattered vascular bundles, therefore, it is not possible to cut the phloem and not the xylem.  As a compromise, a slit is cut about 1/3 way into the stem.  This cuts enough of the vascular bundles to disrupt sufficient phloem translocation while still allowing sufficient water flow in the xylem.


 

TYPES OF LAYERING


air layer


simple layer


tip layer


serpentine layer


trench layer


mound or stool layer

 


Propagation by Grafting and Budding

 

BACKGROUND

Grafting is the technique or process of joining two separate plant parts such that a union (intermingling of newly produced cells) is formed between the two parts, after which they continue growth as one plant.  The upper part of the graft or top of the new plant is called a scion or cion, and the lower part of the graft or bottom of the new plant is called the stock, rootstock or understock.  In some types of grafts a third stem piece is inserted between the scion and stock, which is called an interstock.  Budding is a special type of grafting in which the scion is composed of a single bud or bud piece.  Grafting is a natural process in nature, especially root grafts (this is how Dutch elm disease is spread).

 

The names of the various methods or types of grafting or budding are usually descriptive of the shape, manner or place in which the scion and stock are joined.  In all methods or types, the basic underlying principle is that the cambium of the scion is aligned and placed in intimate contact with the cambium of the stock, such that a successful graft union can be formed.  It is for this reason that grafting is restricted to dicots and gymnosperms, since monocots lack a cambium (with only a few exceptions).  The cambium always occurs just under the bark and outside the woody central cylinder of woody trees.

 

A whip or tongue graft  is used when the scion and stock are approximately equal in diameter.  A cleft graft (or modifications such as the notch, saw -kerf or bark graft) is used when the scion is considerably smaller than the stock.  A T-bud (or modifications such as inverted T, I, patch, plate, flute or ring bud) is used when the bark is slipping (easily peeled).  A chip bud is used when the bark is not slipping (bark is tight and will not peel) (not shown).

 

 


 

TYPES OF GRAFTING

 

TYPES USED TO REPAIR DAMAGE


inarching
(to replace damaged root system)


bridge graft
(to repair damaged trunk)


brace graft
(to support weak branches)

 

TYPES USED WHEN SCION AND STOCK ARE APPROXIMATELY EQUAL IN SIZE


whip or tongue graft


splice graft


saddle graft

 

TYPES USED WHEN SCION IS SMALLER THAN STOCK


side graft


cleft graft


wedge, notch or
saw-kerf graft


bark or bark inlay graft


approach graft


topworking

 


 

TYPES OF BUDDING

 

TYPES USED WHEN BARK IS SLIPPING

Click fro animated T-bud
T-bud

Click for animated inverted T-bud
inverted T- bud

Click for animated I-bud
I-bud

Click for animated patch bud
patch bud

Click for animated ring bud
ring bud

Click for animated flute bud
flute bud

 

 

TYPE USED WHEN BARK IS NOT SLIPPING

Click for animated chip bud
chip bud


 Propagation by Division

 

 

BACKGROUND

 

Division is a propagation procedure in which clumps of plants or individual plant parts, such as rhizomes, tubers or tuberous roots, are cut into sections, thus forming additional individuals from the parent.  Some restrict the definition of division to the separation of plants or plant parts that contain both shoots and roots, and consider the cutting or sectioning of individual plant parts which lack developed shoots and/or roots (shootless rhizomes, tubers or tuberous roots) a special type of shoot or root cutting.

 

Division most commonly is used for the propagation of plants: 1) that due to growth habit form clumps of growth or rosettes, 2) that are impossible to propagate by other methods (cuttings, layering, grafting, or budding) due to variegation (chimeras), due to the inherent inability to produce roots and/or shoots, or due to size.  In addition, division is used commonly as a repotting procedure for plants that have overgrown their pots.

 

 


Propagation by Tissue Culture

 

BACKGROUND

 

Tissue culture (often called micropropagation) is a special type of asexual propagation where a very small piece of tissue (shoot apex, leaf section, or even an individual cell) is excised (cut-out) and placed in sterile (aseptic) culture in a test tube, Petri dish or tissue culture container containing a special culture medium. 


Overview of the Tissue Culture Process

 

The culture medium contains a gel (agar) with the proper mixture of nutrients, sugars, vitamins and hormones, which causes the plant part to grow at very rapid rates to produce new plantlets.  It has been estimated that one chrysanthemum apex placed in tissue culture could produce up to 1,000,000 new plantlets in one year.  Thus, tissue culture is used for rapid multiplication of plants.  A very specialized laboratory is required for tissue culture.  All the procedures are done in a laboratory and special ventilated cabinet that is as sterile as an operating room.

 


Steps in Tissue Culture

(images courtesy of  Dr. Dan Lineberger

aggie-horticulture.tamu.edu/tisscult/microprop/microprop.html)

 

Explant:  Cut-out Plant Tissue and Place in  Tissue Culture Container

The first step is to obtain what is called and explant.  An explant is a very small piece of leaf,  stem, flower or root tissue, the growing point , or even isolate individual cells that are cut and removed from the plant and placed in a tissue culture container.  The tissue has to be sterilized so it will not have any contaminating bacteria or fungus.  It is then placed inside the tissue culture contain on a gel called agar.  In the agar is dissolved all the sugar, nutrients and hormones the plant needs.

 
Explants can be pieces of  any part of the plant (leaves, stems, flowers, etc.),
or even individual isolated cells.

 

Multiplication:  Tissue Grows and Produces Small Plants

 

tissue culture callus

The tissue will begin to grow.  It may make a big blob of tissue called callus, or it may make new shoots directly from the explant tissue that was inserted in the container.  A mass of callus tissue is formed that is just starting to make new plantlets.

 

tissue culture organogenesis

New plantlets (shoots with leaves) are forming.

 

tissue culture multiplication

If the conditions are right a small "forest" of plants will develop in the tissue culture container.

 

Rapid Multiplication by Transfer of Cultures

Once the plantlets start developing, some can be removed and placed in new tissue culture containers.  Thus, another "forest"' of plants is produced.  This results in a rapid multiplication of the cultures and many thousand of plants can be produced in a few months.

 

culture containers

Some of the small plantlets can be removed and transferred to new tissue culture

containers.  These will produce more shoots and fill the container.

 


Transplanting

When the plantlets are large enough, they can be removed from the tissue culture container and transferred into pots with potting soil.  The young plants are growth in a greenhouse just like you would any young seedling or cutting.

transplanting
When the small plant clones are removed from the culture containers, they must be transplanted into some type of acclimation container or  kept under a mist system until the acclimate to the ambient environment.

 

tissue culture transplant
After acclimation, the young plants can be transplanted and grown in pots in a greenhouse to produce new plants.


 

Tissue Culture Transfer Protocol

 

Dr. Dan Lineberger of Texas A&M University demonstrates the protocol to transfer African violets from tissue culture containers where they were grown into a small “forest” of cloned plants (called multiplication culture tubes) to tissue containers where the young clones will form new roots.  After the roots are formed, they can be removed and potted into containers.  This procedure must be done in the sterile environment of a transfer hood.

disinfect surfaces

Sterilize the surfaces of the transfer hood.

disinfect instruments

Sterilize all tools that touch the plants by first dipping in alcohol them flaming.

culture tube

African violet clones in a shoot multiplication tube.

remobe culture

Remove the cluster of plants in the culture.

insert culture

Insert the cluster of plants into the new culture container.

new culture

Break up the cluster of plants and spread them out.

seal lid

Seal the container with paraffin film.

culture before and after

The culture before transfer (left) and after transfer (right).

 


SEXUAL or SEED PROPAGATION

 

The life cycle of plants can be divided into two phases, 1) the vegetative cycle and 2) the sexual reproductive cycle.  Sexual propagation is propagation through seeds, which are the result of the sexual reproductive cycle.

 

The vegetative cycle is called more correctly the sporophyte generation, and the vegetative plant body, which is produced by mitosis, is the sporophyte (2N).  The sexual reproductive cycle is called more correctly the gametophyte generation that, by meiosis, produces the gametes, which are the sex cells (1N).  The male gametes (microspores) develop into the pollen grains (lN) and the female gamete (megaspore) develops into the egg (1N)(see Fig. 9-lA and B).  Pollination is the deposition of pollen grains on the stigma of the pistil of the flower (Fig. 9-1B).  Fertilization is the union of the nuclei of the pollen grains (male gametes or sperm, 1N) with the nucleus of the egg (female gamete, 1N); the fertilized egg is then called a zygote (2N)(Fig. 9-1B).  Flowering plants (Angiosperms) have double fertilization, in which 1 pollen grain nucleus (1N) unites with the egg nucleus (1N) to form a zygote (2N), and one pollen grain nucleus (1N) unites with two polar nuclei (each 1N) to form the endosperm (3N).

 

SEED DORMANCY

 

BACKGROUND

Dormancy is any state of inactive growth, and can be divided into two types: 1) rest, which is often called physiological dormancy, is imposed by internal or physiological factors, and 2) quiescence, which is dormancy imposed by external or environmental factors.  Seeds may possess either or both types of dormancy.  Most seeds are dry at maturity, but will not germinate if sown immediately after extraction from the fruit.  They usually have to be stored 4-8 weeks; this is called an after-ripening period.  After the after-ripening period is satisfied, most seeds will not germinate if keep dry due to quiescence.  Exceptions are short-lived seeds such as oak and maple that do not completely dry and germinate as soon as they are shed from the tree.  In rare cases, seeds of some plants start germinating in the fruits while still attached to the parent plant; this, is called vivipary.  Examples are pecan and citrus.  Once after-ripening has been satisfied, most seeds will germinate immediately if sown in a moist medium.  Examples are most vegetable seeds (bean, tomato, pea, okra, etc.) and many flowering plant seeds (petunia, marigold, coleus, etc.). However, many seeds will not germinate when given the proper environmental conditions due to other dormancy factors.  Stratification and scarification are techniques of overcoming dormancy in these seeds.

 

Stratification is a technique of cold (35-40 oF) moist (in a moist but not wet medium) storage for 6-12 weeks in order to overcome embryo rest (also called physiological dormancy).  The cold moist treatment probably allows a decrease in inhibitors of germination and/or an increase in promoters of germination and, hence, is a true physiological response.  In nature, the cold of winter and moisture of soils result in natural stratification. The seeds of many temperature plant species require stratification for germination.

 

Scarification is a mechanical (physical) or chemical treatment to break, abrade or weaken the hard seed coat present on some seeds.  The hard seed coat prevents germination by either: 1) inhibiting water absorption (most common), 2) inhibiting oxygen uptake, or 3) physically preventing embryo expansion and emergence.  Since the hard seed coat is an external factor that imposes dormancy by maintaining the embryo in an unfavorable environment, it is a type of quiescence.  This type of seed dormancy is often called seed coat dormancy or hardseededness.

 

Types of Seed Dormancy

Seed Dormancy & What Causes

Type Dormancy

How Overcome?

1) Dry Seeds:
    dehydration of seed

quiescence

sow in moist environment 

2) Seed Coat Dormancy or
    Hardseededness:
    hard seed coat impermeable
    to water and gases

quiescence

scarification - physical or chemical
                        abrasion of seed coat.

3) Embryo Rest:
    low growth promoters and/or
    high growth inhibitors 
    in embryo

 rest 
(physiological
dormancy)

stratification - cold (35-40 oF),
       moist storage for 4-12 weeks. 

4) Double Dormancy:
    hard seed coat plus embryo
    rest

both quiescence
and rest

scarification then stratification

5) Chemical Inhibitors:
    inhibitors in pericarp (fruit 
    wall) or testa (seed coat)

correlated
inhibition

1) if fleshy, remove fleshy pericarp
    (fruit wall) or testa (seed coat). 
2) if pericarp or testa is dry, leach
    in running watery. 

6) Immature Embryo:
    underdeveloped or 
    rudimentary embryo 

developmental
dormancy

1) after ripening - store for 4-6 
    weeks under ambient conditions. 
2) warm stratification - warm 
    moist storage. 
3) embryo culture - excise 
    embryo and put in tissue culture.

7) Light Requirement
    phytochrome in Pr form

secondary
dormancy

1) expose to any white light 
2) expose to red light 
3) sow shallow or on surface


Types of Seed Scarification

 

Natural scarification to soften hard seed coats may occur in several ways: 1) mechanical (physical) abrasion, 2) alternate freezing and thawing, 3) fire, 4) attack by microorganisms (fungi and bacteria), or 5) passing through the digestive tract of birds and mammals.  Seeds with very hard seed coats may remain dormant for several years before these natural mechanisms sufficiently soften the seed coats.

 

Artificial scarification is frequently used by horticulturists to hasten germination.  The three most commonly used techniques are as follows:

 

1)   Mechanical (physical) scarification.  This is the most commonly used method.  The hard seed coat is mechanically or physically abraded by a variety of means, such as: a) rubbing on sandpaper, b) filing with a flat or triangular file, c) nicking with a knife,  d) cracking with a hammer, pair of pliers or pecan cracker or e) tumbling in a cement mixer with sand.

 

2)   Hot water soak.  Some seeds can be soaked in hot water to soften the seed coat.  The seeds are placed in 4-5 times their volume of water heated to 170-212oF (77-100oC).  The water is removed from the source of heat and the seeds are immediately immersed and soaked 12-24 hours in the gradually cooling water.  Some seeds my be sensitive to the hot water treatment.

 

3)   Acid (chemical) scarification.  The seeds are soaked in concentrated sulfuric acid (H2SO4 ), which chemically breaks down (oxidizes) the hard seed coat.  This  is a very effective method, but should only be attempted by an experienced person.  Sulfuric acid is highly corrosive (to both the seed and you) and reacts violently with water to cause instant boiling and splattering, hence, protective clothing and eye goggles must be worn.  Dry seeds are placed in a glass or earthenware container (do not use metal or plastic containers), and approximately twice their volume of concentrated sulfuric acid is added, followed by occasional gentle stirring (to avoid over-heating and splattering).  The seeds are allowed to soak from 10 minutes to 6 hours, depending on species.  An average scarification time would be 15 minutes to 2 hours, but small lots should be tested for the optimum time as demonstrated in this exercise.  The acid is carefully poured off.  Small volumes of waste acid can be neutralized with base, but it is best to store the waste acid in a glass vessel and dispose it through a professional waste disposal company.  The seeds are washed for several minutes under large amounts of running tap water to remove all acid, then sown immediately or dried and stored.

 

Scarification Followed by Stratification.  Some seeds exhibit a double dormancy due to both hard seed coat dormancy and embryo rest.  A combination of scarification followed by stratification is necessary to overcome double dormancy and allow germination.  The scarification treatment must be carried out first to allow the seed to imbibe water, since stratification requires the seed to be imbibed.


 

How to Scarify Seeds

 

 

Mechanical Scarification.

Methods include:

  1. File down the seed coat with a triangular file
  2. Nick the seed coat with a knife or hand pruning shears.
  3. Place seeds in drum with sand and tumble the drum.
  4. Hold the seeds against a grinding wheel.

Do not cut into and damage the tissue inside the seed or the seed will likely rot.

 

Hot Water Soak.  

  1. Bring a beaker of water to a boil and remove from the heat. 
  2. Completely immerse the seeds in the beaker of water (170-212oF). 
  3. Set the beaker aside to cool for 24 hours.
  4. Sow the seeds.

 

Sulfuric Acid (H2SO4) Scarification.

  1. Place seeds in a dry glass beaker. 
  2. Put on a pair of rubber gloves, a plastic apron and goggles or glasses. 
  3. VERY CAREFULLY and SLOWLY pour enough sulfuric acid over the seeds to completely immerse them (at least twice their volume). 
  4. Set the beaker aside and periodically (approximately every 5 min.) slowly stir the seed/sulfuric acid solution. 
  5. After 10-30 minutes, remove the seeds by decanting into a funnel suspended in a beaker. 
  6. Washed the seeds under running water for 10 minutes.
  7. Sow the seeds

 


 

SEEDS THAT REQUIRE

STRATIFICATION AND/OR SCARIFICATION FOR GERMINATION

Require
Stratification
(6-12 wks @ 35-40°F)

Require
Scarification
(mechanical or acid)

Require
Scarification then
Stratification

Apple
(Malus sylvestris)

Black Locust
(Robinia pseudoacacia)

American Linden
(Tilia americana)

Cherry
(Prunus sp.)

Bluebonnet
(Lupinus texensis)

Cotoneaster
(Cotoneaster sp.)

Dogwood
(Cornus sp.)

Clover
(Trifolium sp.)

Golden Rain Tree
(Koelreuteria paniculata)

Euonymus
(Euonymus alatus)

Coontie
(Zamia sp.)

Hawthorn
(Crataegus sp.)

Holly
(Ilex sp.)

Honey Locust
(Gleditsia triacanthos)

Persimmon
(Diospyros virginiana)

Magnolia
(Magnolia sp.)

Mimosa
(Albizia julibrissin)

Redbud
(Cercis canadensis)

Maple
(Acer sp.)

Peanut Tree
(Sophora secundiflora)

Russian Olive
(Elaeagnus angustifolia)

Peach
(Prunus persica)

Sago Palm
(Cycas revoluta)

 

Pear
(Pyrus communis)

 

 

Pecan
(Carya illinoensis)

 

 

 

 


Soil and Soilless Growing Media

David Wm. Reed

Professor of Horticulture

Department of Horticultural Sciences

Texas A&M University

 

 

Soil, Growing Medium and Amendments

 (primarily taken from David Wm. Reed, General Horticulture Laboratory Manual,

2nd ed. Burgess Publ., Edina, Mn)

 

Soil

Soil is the outer weathered portion of the earth's crust.  Sometimes it is called field soil.  It is very important to realize that soil is differentiated from dirt, in that dirt is that which occurs under your fingernails.  A thorough understanding of the nature and properties of soils is essential for field production of fruits, vegetables, turfgrasses, and ornamentals that are field grown or planted in the landscape.

 

Why field soil is not used for growing plants in containers?

Potting Soils, soilless growing media, or artificial growing media are used in the production of horticultural plants in containers, such as in outdoor container nurseries, greenhouse pot plant production, and indoor gardening and landscaping.  Pure field soils are unsuitable for container growing.  In the small volume of containers, soil packs excessively and forms many small pores.  Both of these factors decrease aeration (air movement and exchange) and drainage (water movement and exchange).  However, many artificial growing media may contain up to 25% to 50% of their volume as field soil.  The value of using some soil as a component of the growing medium is that it supplies many micronutrients and beneficial microorganisms.

 

The Dynamic Nature of Soil and Growing Media


Soil Texture

Background

Most soils on the average are composed of 46-49% mineral particles (often called separates), 1-6% organic matter and 50% air and water.  The mineral particles of soil are sand, silt and clay.

 

Size and Characteristics of Soil Mineral Particles

Mineral
Particle

Size

Characteristics

sand

0.05-2 mm

Relatively inert; small total surface area; forms large pores; increases drainage and aeration; poor nutrient holding capacity

silt

0.002-0.05 mm

Intermediate between sand and clay

clay

less than 0.002 mm

Chemically and structurally complex (negatively charged and laminated); large total surface area; forms very small pores; increases water and nutrient holding capacity; may decrease aeration and drainage if poor structure.

 

Soil texture refers to the relative proportion (by weight) of sand, silt and clay present in soil.  This is differentiated from soil structure, which is the physical arrangement or grouping together of the individual soil mineral particles.  Soil texture is very important in that it effects: 1) soil structure, 2) water holding capacity, 3) nutrient holding capacity, 4) aeration, 5) drainage, and 6) root penetration and growth.

Soil texture triangle.

 

The soil texture triangle shows the percentage (by weight) sand, silt and clay in the various textural classes of soils.  The various textural classes denote a range of texture combinations which have similar chemical and physical properties, and yield similar plant growth.  Generally, a loam soil is considered the best for overall plant growth.  For example, a soil that was found to contain 20% sand, 20% clay and 60% silt would be classified as a silt loam.

 

Amendments

Used to improve Field Soil

Used to Make Soilless Potting Soils

Background

For growing plants in container, the use of pure field soil is not recommended.  The soil tends to become compacted, which:  1) decreases drainage (water movement and exchange) and 2) decreases aeration (air movement and exchange).  In addition, soils are 3) heavy (increases shipping cost, and physical labor), 4) a good source is often hard to obtain, and 5) all soils must be sterilized to remove pathogens, nematodes and weeds.  For these reasons, the soil is usually amended or completely replaced with various organic and inorganic materials, which are commonly called amendments.  Growing medium amendments may be either organic or inorganic.  The most commonly used growing medium amendments and their properties are listed in Tables on the following pages.

 

Soil. Amendments are added to soil to increase aeration, drainage and/or fertility.  It commonly is recommended to incorporate into ground beds 2 to 3-inches of organic matter or compost.  In addition, a 2 to 3-inch layer of mulch commonly is recommended.  Almost any form of organic matter and inorganic materials can be used as a mulch (assuming it does not contain toxic compounds), but not all of which would be recommended for incorporation into the ground bed.  The section below on composting and C:N ratio will explain why.

 

Organic Amendments.

Organic growing medium amendments usually are derived from plants or plant products that occur naturally (peat moss from peat bogs), or are the by-products of processing plants or mills (sawdust, cedar chips, bark, bagasse, rice hulls) or waste disposal plants (processed sewage sludge).  The main purpose of using organic amendments is to loosen the soil and create large pores to increase 1) aeration, 2) drainage, 3) usable water holding capacity, 4) nutrient holding capacity, and 5) decrease growing medium weight (compared to soil).

 

By far the most commonly used organic amendment is peat moss.  Sphagnum peat moss is the highest quality and is dug from drained and dried peat bogs which contain at least 75% sphagnum moss.  The main sources are Germany, Canada and Ireland.  Hypanaceous or domestic peat is of lower quality, is more highly decomposed, is not as long lasting as sphagnum peat moss, and are usually from temperate N. American.  Muck peat is low quality, very fine, highly decomposed, and generally is not recommended.  Bark is from both hardwood and softwood trees, is commonly used for large containers, outdoor container production and landscape planting.  Sawdust is often used for amending outdoor plantings.  The other amendments are used less frequently.  The use of many organic amendments is based on what is available locally. 

 

Composting

Before incorporating into ground beds, most organic amendments, especially sawdust, cedar chips, bark and bagasse, should 1) be composted or aged, and 2) sterilized before use if possible.  All of these amendments have a high C:N ratio.  Use of uncomposted amendments that have a high C:N ratio will: 1) deplete the N from the soil, 2) may cause a salt or ammonia/ammonium burn, or 3) may cause damage due to heat build up.  Amendments with a low C:N ratio will release N upon further decomposition, thus act as an organic fertilizer.  However, organic matter with a low C:N ratio also should be composed to avoid rapid ammonia/ammonium release and toxicity.  Below is a list of commonly used amendments and their C:N ratio.

 

Low C:N

(releases N upon decomposition)

manure

5-25:1

alfalfa hay

13-1

vegetable scraps

15-20:1

coffee grounds

20:1

grass clippings

15-25:1

High C/N

(depletes N upon decomposition)

autumn leaves

30-60:1

straw

40-100:1

bark

100-130:1

mixed paper

150-200:1

wood chips or sawdust

400-500:1

newspaper or corrugated cardboard

200-500:1

 

Inorganic Amendments

Most inorganic amendments are mined from natural deposits and further processed to yield the final product (ex. perlite, vermiculite, sand and calcined clay).  Some are totally artificial or synthetic (styrofoam beads) and some are from plant sources (rice hull ash).  Inorganic amendments are used to: 1) increase aeration, 2) increase drainage, 3) decrease excessive water holding capacity, and 4) decrease or increase weight.  Most are relatively sterile (in regard to plant pathogens) and many are relatively inert.

 

Sand was used extensively in the past, but due to its greater weight is used less frequently today. Vermiculite is used commonly for seedlings, bedding plant, and flowering pot plant production.  Vermiculite naturally contains a high content of potassium (K) and magnesium (Mg), hence, supplies much of what is needed by the plant.  Perlite is used because of its light weight and inertness.  Perlite may contain high fluoride (F), which is toxic to many foliage plants.  Styrofoam beads often are used in place of perlite, mainly due to styrofoam's lower cost, and to avoid the potential for fluoride (F) toxicity from perlite.  Calcined clay or haydite (and similar fired clay products) are used when larger aggregates are desired, such as large containers, landscape plantings, golf greens and hydroponics.


ORGANIC AMENDMENTS USED IN GROWING MEDIA

Amendment

Source

Size

Wt.

Useful Life

pH

CECz

Sterile/
Contaminants

C/Ny Ratio

% (By Volume) Recommended

sphagnum peat moss  (best quality)

min. 70% sphagnum peat bogs (Germ., Can., Ire.)

fine to coarse

light

3-5 yrs

acidic 4-5.5

high

relatively sterile/none

med

25-75%

hypanaceous peat moss  or domestic peat,(med quality)

hypanaceae or sedge peat bogs
(northern
U.S.)

inter-mediate

light

2-3 yrs

acidic 4.5-5.5

high

relatively/none

med

25-75%

muck peat moss (poor quality)

highly decomposed peat/ plant bogs
(southern
U.S.)

very fine

light

short, 1 growing season

acidic 4.5-5.5

high

---

med

25-50%

Bark (shredded or ground)

hardwood & softwood trees, many species used

fine to coarse

med

up to 3-5 yrs; spp. depend.

4-5.5

med

No/resins

med

25-75%

sawdust or wood shavings

hardwood & softwood trees

fine to coarse

light

up to 3-5 yrs; spp. depend.

4.8-6.8 spp. depend.

med

no/some resins

very high

25% max

cedar chips

cedar heart wood chips after oil is extracted

coarse

med

as sawdust

6.0

low

relatively/resinsoil

high

25% max

bagasse

sugar cane pulp

variable

light

up to 1-3 yrs (com-posted)

acidic

med

no/sugar, Mn

high-very high

25% max

rice hulls

hulls (shells) of rice

med

very light

up to 1 growing season

neutral

low-med

no/silica

high

25% max

processed sewage sludge

municipal sewage treatment plants

very fine to coarse

light-med

2-3 yrs

acidic 5.0

med

no (human viruses)/heavy metals

med

25% max

zCEC = cation exchange capacity,  indicates nutrient holding capacity or potential fertility.
yC/N = ratio of carbon to nitrogen.  High C/N ratio depletes soil nitrogen; and low C/N ratio releases nitrogen into medium.

 


INORGANIC AMENDMENTS USED IN GROWING MEDIA

Amendment

Source

Process

Size

Weight
(lb/ft
3)

Useful Life

pH

CECz

Steriley/
Contaminants

% (By Volume) Recommend

perlite

aluminum-silica volcanic rock

crush; heated to 1800°F to expand

use horticultural grade

4-8

infinite, unless crushed

7.0-7.5

none

yes/fluoride (F)

25-50%

vermiculite

mica mineral

crush; heated to 1400°F to expand

use horticultural grade (#2, 3, or 4)

4-10

use media only once, compresses easily when wet

Amer.-7-7.5 S. Afr.-9.8

very high (20-60)

yes/6% K (K2O), 20% Mg (MgO)

25-50%

styrofoam beads (poly-styrene)

polystyrene

by-product of polystyrene processing

variable, use ¼ to ½ cm

very light

infinite, unless heated or disinfected

neutral

none

yes/none

25-50%

sand

sand pits, dunes or river bottoms

dug & washed

use coarse, sharp sand, 0.25-0.5 is best

100


infinite

variable
mostly neutral

very low

no/none if well washed

25-25%

calcined clay or haydite

montmorillonite & attagulgite clays

grade particles, heat (fired) to 1300°F to harden

variable

38

virtually infinite

-

med-high

no/none

20-25%

rice hull ash

rice hulls

combustion of rice hulls (for energy)

like fine sand

50-80

infinite

9.3

med-high

yes/97% silica dioxide

20-25%

zCEC = cation exchange capacity, indicates nutrient holding capacity or potential fertility.
yNOTE:  Many of these are sterile after being processed, but may become contaminated later.


How to make Soilless Growing Medium Mixes

 

Background

 

Soil-containing Mixes

Some of the first standardized growing medium mixes were the U.C. (Univ. of California) soil mixes.  They all contain various proportions of sand and peat moss.  A starter fertilizer is usually added directly to the mix, which must be followed-up with routine fertilization.  Preferably, sphagnum peat moss and coarse sand should be used.  Other organic amendments may be substituted for the peat moss.  Many nursery crops are grown in containers in a modified U.C. mix containing 75-80% bark, instead of peat moss, and 20-25% sand.

 

Soilless Mixes

Due to: 1) the heavy weight of sand and soil, 2) increasing cost, 3) decreasing availability, and 4) the need for sterilization of any medium containing soil, the U.C. mixes, and soil mixes in general, increasingly are being replaced by soilless (often called artificial) growing media.  The most commonly used soilless growing media are the Peat-Lite Mixes.  Peat-Lite Mix A contains 1 part peat moss: 1 part vermiculite plus fertilizer and lime, and was developed specifically for bedding plants, young seedlings and to a lesser degree flowering pot plants.  Peat-Lite Mix B contains 1 part peat moss: 1 part perlite plus fertilizer and lime, and was developed for larger plants and plants that require more drainage than is afforded by Peat-Lite Mix A. The Peat-Lite Foliage Plant Mix was developed specifically for foliage plants, and is a hybrid of Mix A and Mix B containing 2 parts peat moss: l part vermiculite: l part perlite plus a little extra fertilizer (10-10-10) and iron (Fe sulfate).  Most foliage plants grow just as well in Mix B.  The Peat-Lite Epiphytic Mix was developed for plants (epiphytes, orchids, bromeliads, some ferns, cacti and succulents) that require excellent aeration and drainage.  In all the Peat-Lite mixes, bark is often substituted for peat moss for larger containers.

 

Commercial Growing Mixes

Many pre-mixed growing media, often called "potting soils", are sold commercially in retail nurseries and stores that sell gardening supplies.  The best are soilless and contain sphagnum peat and/or bark with perlite, vermiculite, and/or styrofoam.  Many of these are modifications of the Peat-Lite mixes.

 

The quality of commercial "potting soils" ranges from very poor to excellent.  BEWARE of any commercial mix that does not contain 50-75% good quality peat moss, preferably sphagnum or a coarse well-composted bark.  The mixes should also contain at least 25% of a coarse amendment (sand, perlite, styrofoam, haydite, etc.) to allow adequate drainage and aeration.  The numerous very fine muck-type commercial mixes: 1) are of much poorer quality, 2) have a short life (one growing season at best), 3) have poor drainage and aeration, and 4) usually result in poor growth or death unless watering, fertility and light are closely and expertly monitored.


 

U.C. (University of California) Soil Mixes

U.C.

% By Volumez

Weight

 

 

Soil Mix

Sand

Peat

(Moist)
lb/ft
3

Properties and Uses

Plants

A

100

0

117

seldom used, too heavy & poor nutrient holding capacity; large pots, flats & ground beds and hydroponics

 

B

75

25

105

good physical properties; large pots, flats & ground beds; plants requiring moderate aeration

carnation, rose, ivy, geranium, palm, cacti, succulents

Cy

50

50

94

commonly used, excellent physical properties; pots & ground beds; plants requiring moderate aeration

most foliage and flowering plants; chrysanthemum, ivy, peperomia, hydrangea, ficus, poinsettia, philodendron

D

25

75

66

commonly used, light weight, excellent aeration; pots & ground beds; plants requiring medium to high aeration

begonia, African violet, gloxinia, snapdragon, camellia, gardenia, rhododendron

E

0

100

43

very light weight, excellent aeration; pots; plants requiring high aeration

azalea, camellia, gardenia, ferns

zUse coarse washed sand and sphagnum peat moss.  Composted bark, redwood shavings, sawdust or rice hulls may be substituted for part or all of the peat.

yFertilizer - for a starter fertilizer, for Mix C, add per cubic yard:  4 oz potassium nitrate, 4 oz potassium sulfate, 2½ lb single superphosphate, 2½ lb calcium carbonate lime, and 7½ lb dolomite.


PEAT-LITE MIXESz

Peat-lite

To Make 1 Cu Yd

Uses/Plants

Mix A
shredded sphagnum peat moss
horticultural vermiculite #2, 3 or 4
ground limestone
superphosphate, 20%, powdered
calcium or potassium nitrate
fritted trace elements (FTE No. 503)
nonionic liquid wetting agent


11 bushels (bu)
11 bu
5-10 lbs
1-2 lbs
1 lb
2 oz
3 oz


bedding plants; seedlings; flowering pot plants; any small containers

Mix B
shredded sphagnum peat moss
horticultural grade perlite
ground limestone
superphosphate, 20%, powdered
potassium nitrate (14-0-44)
fritted trace elements (FTE No. 503)
nonionic liquid wetting agent


11 bu
11 bu
5-10 lbs
1-2 lbs
1 lb
2 oz
3 oz


flowering pot plants; also many foliage plants, especially those requiring good drainage, ex. asparagus, peperomia, chlorophytum, cacti or hanging baskets, succulents; propagation

Foliage Plant Mix
sphagnum peat moss (½" mesh)
horticultural vermiculite (No. 2)
perlite (med grade)
ground dolomitic limestone
superphosphate, 20% powdered
10-10-10 fertilizer
iron sulfate
potassium nitrate (14-0-44)
fritted trace element mix
granular wetting agent


11 bu
5½ bu
5½ bu
8¼ lbs
2 lbs
2¾ lbs
¾ lbs
1 lb
2 oz
1½ lbs


excellent all-purpose mix; most foliage plants and flowering pot plants; hanging baskets

Epiphytic Mix
sphagnum peat moss (screened ½" mesh)
Douglas, red, or white fir bark(1/8-1/4")
perlite (med grade)
ground dolomitic limestone
superphosphate, 20% powdered
10-10-10 fertilizer
iron sulfate
potassium nitrate (14-0-44)
fritted trace element mix
granular wetting agent


7 bu


7 bu
7 bu
7 lbs
4½ lbs
2½ lbs
½ lbs
1 lb
2 oz
1½ lbs


plants requiring good drainage and/or a coarse medium; orchids, bromeliads, ferns, some cacti and succulents

zIn place of perlite; sand, calcined clay, haydite or rice hull ash may be substituted to increase weight; and styrofoam beads increasingly are substituted  due to the greater cost and potential fluoride (F) toxicity of perlite.  In place of peat; a relatively fine, well composted bark may be substituted for large containers, woody plants, or for better drainage.


Simple Soil and Water Testing

David Wm. Reed

Professor of Horticulture

Department of Horticultural Sciences

Texas A&M University

 

 

How to Measure Total Porosity of Soil and Growing Media

and

Effect of Mixing Coarse Aggregates

(modified from Spomer 1979 and Reed 1985)

How to Measure Porosity and Aeration

1.      Add a measured volume of peat or bark to a beaker.  Tap the beaker lightly on the table to settle the mixture.

2.      Add a measured volume of another amendment, such as sand, fine vermiculite, medium vermiculite, perlite, styrofoam, etc., to another beaker.  Tap to settle.

3.     

____________ml

missing volume = “shrinkage”

(D=(A+B)-C)

 

 

____________% “shrinkage”

 

Mix the 2 amendments uniformly in a plastic bag.  Add all of the mixture (every last bit) to a larger beaker.  Tap to settle.  Measure the volume and record on the diagram below.

 


Thought Provokers

Where did the medium go?  Is it magic?

Draw an analogy of pouring sand into a beaker of marbles.

How will this effect aeration and drainage?

Which type of amendments can be mixed without shrinkage?

How much of a course amendment must be added to increase aeration and drainage?

Will sand increase drainage of peat or bark?

Will sand increase drainage of soil, and if so how much? (hint look at the soil texture triangle)


How to Measure Aeration and Water Holding Capacity of Soil and Growing Media

(modified from Spomer 1979 and Reed 1985)

 

Procedure

1.      Tape over the holes of a 4” plastic pot.  Cover the inside bottom with a layer of cheese cloth or screen.

2.      Fill the pot with a measured amount of dry medium (about 300 ml in a 4” pot) and record the volume on the diagram on the next page (A).  Tap the pot lightly several times on the table to firm and settle the medium.

3.      Add water slowly until the medium is saturated and water is just even with the top level of the medium.  Use a graduated cylinder or beaker to pour the water and keep track of how much water is added.  Record the volume of water added on the diagram on the next page (B).  This is a measure of the total porosity (air + water) of the medium.

4.      Remove the tape from one hole and collect in a beaker all the water that drains out of the container.  Record the volume of water collected on the diagram on the next page (D).  The volume of water collected is equal to the air pore space.

5.      Make the appropriate calculations indicated in the diagram on the next page, and compare the results with the suggested values in the table below.

 


 

 


 


Expected Numbers for Sphagnum Peat Based

(Peat-Lite) Growing Media*

% Water Holding Capacity (v/v)                    70%

% Aeration (v/v)                                            9-10%

% Total Porosity (v/v)                                    85-88%

*from Fonteno, W.C., Growing Media: Types and Physical/Chemical Properties, In Water, Media and Nutrition for Greenhouse Crops, D.W. Reed, Editor, Ball Publishing, Batavia, IL, 1996

 

THOUGHT PROVOKERS

What happened to aeration, water holding capacity and, hence, drainage upon mixing?

What size amendments can be mixed together without decreasing aeration and drainage?

If this is all true, then what is the advantage, if any, of using coarse aggregates, such as perlite, in a growing medium?


Measuring EC and pH of Soil and Growing Media

 

Sampling and Sample Preparation

·        Select several (5-10) pots from across the bench or locations in a ground bed.

·        Collect the growing medium sample from the middle and bottom of the container or bed.  See explanation on the following page.

·        DO NOT collect growing medium from the top layer (top inch or so) of the container or bed.

·        Use a core to extract the medium, or knock the plant out of the pot and collect the sample.

·        Combine the samples to make one pooled sample.

·        Do this for each bench, greenhouse or crop - the more locations you sample the better chance you have to see any variation.

·        Set the samples out to air dry.

Extraction of the Sample for Soluble Salts and pH

·        Prepare a 1:2 dilution, a 1:5 dilution or a saturated paste.

·        For a 1:2 dilution extract do the following:

·        Mix 1 part of air dried growing medium with 2 parts of water.  For example, mix a 2 ounce volume of growing medium with a 4 ounce volume of water.

·        If available, use bottled water purified by distillation or reverse osmosis.  If you use your tap water, you must measure its conductivity and subtract out this reading.

·        Stir the solution and let it sit for 15 to 30 minutes.

 

Filter the Extract

·        Pour the extract through a filter and collect the filtered solution.  You can use a funnel with filter paper, or a coffee filter holder with a coffee filter, or even line a pot with holes in it with a thin, clean, white cloth to make a filter.

·        The filtered solution should be relatively free of media and debris, and may look colored, but not too cloudy.

 

Measure pH with a pH Meter

·        Calibrate the pH meter with buffer solutions according to the manufacturer.

·        Completely immerse the pH electrode into the filtered solution, or pour the solution into the cup of the pH meter.

·        When the reading stabilizes, write down the pH

 

Measure Soluble Salts with a Conductivity Meter

·        Completely immerse the conductivity probe into the filtered solution, or pour the solution into the cup of the Conductivity Meter.  If you use tap water, measure its EC also.

·        Record the electrical conductivity (EC) of the filtered solution.  Subtract the tap water EC.

 

Interpretation of the pH and Electrical Conductivity (EC) Readings

·        Compare the readings to the interpretation tables attached.

 

Tracking the Results over the Life of the Crop

·        Plot the readings on the Graphical Tracking Chart attached.


Where to Collect the Soil Sample in Containers and Ground Beds

 

Soluble salts always build-up to higher levels in the top of the container or at the surface of the soil.  This is because the salts migrate to the top of the growing medium with the water and are left behind upon evaporation.  This leaves a “salt crust” in the top layer.  This occurs with all methods of irrigation, but is more pronounced with subirrigation systems or where there is little leaching.  The same occurs in ground beds or field soils.  This layer must be avoided when collecting growing medium for analysis.

 

 

Location of Soluble Salt Build-Up in the Container

(From D.W. Reed, Closed Production Systems for Containerized Crops: Recirculating Subirrigation and Zero-Leach Systems, In Water, Media and Nutrition for Greenhouse Crops, D.W. Reed, Editor, Ball Publishing, Batavia, IL, 1996)

 

 

 

 

 

 

Therefore:

Containers:        Collect the growing medium sample for analysis from the bottom 2/3 of the growing medium the container

Ground Beds:    Collect the soil from an inch or so below the surface.

 

 


Recommended pH and Electrical Conductivity (EC) Ranges

For Soil and Growing Media of Greenhouse Crops

(from H.J. Lang, Chapter 6 - Growing Media Testing and Interpretation, In Water, Media and Nutrition for Greenhouse Crops, D.W. Reed, Editor, Ball Publishing, Batavia, IL, 1996)

 

 

Recommended pH Ranges

 

                                                SME                       1:2 or 1:5 Dilutions

                                                                                                                  

                            Extracta         Slurryb          Extracta            Slurryb       Pour-Through

                                                                                                                                          

 

Optimum pH        5.5-6.5          5.4-6.2           5.5-6.5             5.4-6.2             5.5-6.5

 

a - Extract is the filtered solution phase of the potting medium-water mixture.

b - Slurry is the mixture of potting medium-water prior to filtering.

 

 

 

 

 

 

Recommended Electrical Conductivity (EC) Ranges

 

                                                              Electrical Conductivity (EC) - dS/ma

                                                                                                                                               

 

                                               SME            1:2 Dilution       1:5 Dilution     Pour-Throughb

                                                                                                                                                                                               

 

      Established plants         2.0-3.0                0.8-1.2                0.3-0.6                3.0-5.0

 

      Seedlings, plugs             1.0-2.0                0.5-0.9                     c                         c

 

a -  For conversion between different units of expressing electrical conductivity:

      1 dS/m = 1 mS/cm = 1 mmho/cm @ 700 ppm

b -  The pour-through method has not been thoroughly tested, and the 3.0-5.0 dS/m level given is based primarily on grower observations.

c -  Optimum level not available.


Graphical Tracking of pH and EC over the Life of Crop or Seasonally

(from H.J. Lang, Chapter 6 - Growing Media Testing and Interpretation, In Water, Media and Nutrition for Greenhouse Crops, D.W. Reed, Editor, Ball Publishing, Batavia, IL, 1996)

 

It is a good idea to graph how the pH, EC, alkalinity or any other test result changes over time.  The line will allow one to clearly notice any trends that are developing, hence predict the future.

CROP:                                                                                             

LOCATION:                                                                                   

DATE OF PLANTING:                                                                   

 

 


Measuring EC, pH and Alkalinity of Irrigation Water

 

Sampling and Sample Handling

·        Collect the irrigation water sample as close to the well head as possible.

·        Turn on the water and let it run for awhile in order to flush out any water that has been setting in the casing of the well and any water lines.

·        Place the water sample in a polyethylene, polypropylene, or no-boron glass container.  If the water is to be tested right away (not stored), most plastic or glass containers can be used.

·        Make sure the container is clean and free of contaminants.

·        Do not use plastic containers if the water is to be tested for herbicides or pesticides.

·        The sample should not be stored longer than overnight before testing or shipping.

 

Measure pH with a pH Meter

·        Calibrate the pH meter with buffer solutions according to the manufacturer.

·        Completely immerse the pH electrode into the water sample, or pour the water sample into the cup of the pH meter.  When the reading stabilizes, record the pH

·        Compare the pH reading to the values in the attached interpretation table.

 

Measure Soluble Salts with a Conductivity Meter

·        Completely immerse the conductivity probe into the water sample, or pour the water sample into the cup of the Conductivity Meter.  Record the electrical conductivity (EC) reading.

·        Compare the EC reading to the values in the attached interpretation table.

 

Measuring Alkalinity with an Alkalinity Test Kit

·        Easy-to-use, inexpensive alkalinity test kits can determine the alkalinity of irrigation water.

·        Follow the directions on the kit you purchase.

·        Compare the alkalinity reading to the values in the attached interpretation table.

 

Interpretation of the pH,  Electrical Conductivity (EC) and Alkalinity Readings

·        Compare the EC and alkalinity readings to the interpretation tables attached.

·        Alkalinity is due to all the bases (the opposite of acids) in irrigation water.  However, for most waters, alkalinity is the about the same as the total of the bicarbonate/carbonate in the water.  Since most waters usually contain only bicarbonate, with little carbonate (unless the water has a very high pH of about 9), alkalinity is usually about the same as the bicarbonate content of most water analyses .  Use the attached interpretation tables to interpret the alkalinity level.

·        Tables also are given for the correction of too high or too low alkalinity.

·        The exact pH is really not that important, unless it is very high or very low.  The most important property that determines the pH of water is the bicarbonate/carbonate content, which is determined by testing the alkalinity of the water.  High pH (i.e. basic or alkaline) water has more bicarbonate/carbonates, and low pH (i.e. acid) water contains less bicarbonate/carbonates.  We ideally want the pH of irrigation water to be about pH 5.8 to 6.5, which really means that there is enough alkalinity in the water to keep the pH up a bit, but not too much to cause the pH to be too high.


Recommended Chemical Properties of Irrigation Water

(From F. H. Peterson, Water Testing and Interpretation, In Water, Media and Nutrition for Greenhouse Crops, D.W. Reed, Editor, Ball Publishing, Batavia, IL, 1996)

 

 

Relative Hazard

Chemical Property

None

Little

Moderate

High

Severe

 

 

 

me/la

 

 

Bicarbonate

<2

2-3

3-4

4-6

>6

Chloride-Foliar

<3

 

 

 

 

Chloride-Root

<4

 

4-6

6-10

>10

Sodium-Foliar

<3

 

 

 

 

Sodium-Root

<3

 

3-9

 

>9

 

 

 

ppma

 

 

Bicarbonate

<122

122-183

183-244

244-366

>366

Chloride-Foliar

<106

 

 

 

 

Chloride-Root

<142

 

142-213

213-355

>355

Sodium-Foliar

<69

 

 

 

 

Sodium-Root

<69

 

69-207

 

>207

Lithium

<2.5

 

 

 

 

Zinc

<2

 

 

 

 

Iron

<1

 

 

 

 

Manganese

<1

 

 

 

 

Fluoride

<1

 

 

 

 

Boron

<0.3

0.3-0.5

0.5-1.0

1.0-2.0

>3

Copper

<0.2

 

 

 

 

 

 

 

dS/mb

 

 

Electrical Conductivity (ECw)

0.2

<0.7

0.7-2

2-3

>3

Adjusted Sodium

 

 

unitless

 

 

Absorption Ratio(Adj RNa)

<3

3-6

6-8

8-9

>9

 

a -  Micronutrients and trace minerals usually are reported in ppm; nutrients and minerals present in larger quantities are often reported in ppm and/or milliequivalents/liter (me/l); the following conversions can be used:
sodium -        ppm = (me/l)(22)
chloride -       ppm = (me/l)(35.5)
bicarbonate - ppm = (me/l)(61)

b -  The trend is to report electrical conductivity as deciSiemens/meter (dS/m).  Some labs still report milliSiemens/centimeter (mS/cm) or millimho/centimeter (mmho/cm).  There is no need for conversion because they are all equal: 1 dS/m = 1 mS/cm = 1 mmho/cm ~ 700 ppm.


Interpretation of Alkalinity Levels of Irrigation Water

(Taken from D. A. Bailey, Alkalinity, pH and Acidification, in Water, Media and Nutrition for Greenhouse Crops, D.W. Reed, Editor, Ball Publishing, Batavia, IL, 1996)

 

Alkalinity levels somewhere in the range of 40 to 130 ppm are acceptable, and even recommended.  A certain degree of alkalinity will keep the soil or growing medium from becoming too acid or too basic over time due to other factors.

Recommended Alkalinity Levels

The values indicate the minimum and maximum alkalinity levels in irrigation water.

                                                                     Minimuma                                        Maximumb

Product Being Grown                           ppmc                meq/lc              ppmc                meq/lc

Plugs and/or seedlings                             38                    0.75                 66                    1.3

Small pots and shallow flats                     38                    0.75                 86                    1.7

4" to 5" pots and deep flats                     38                    0.75                 106                  2.1

6” pots and long term crops                    63                    1.25                 131                  2.6

a -    If media pH declines during production, add potassium bicarbonate to at least this level.

b -   If media pH rises during production, acidifying the water if alkalinity is above this level.

c -    to convert between ppm and meq/l:                  ppm        =      (meq/l) X (50);           meq/l      =      (ppm) / (50)

 

Correcting Alkalinity of Irrigation Water

If the alkalinity of irrigation water is too high or too low, it can be corrected by adding bicarbonate or acid to the irrigation water according to the following

Increase Alkalinity of Irrigation Water

The values indicated the amount of potassium bicarbonate to add to irrigation water to increase alkalinity and the corresponding amount of potassium added.

Alkalinity                             Amount of potassium                      Potassium

Desired                                bicarbonate needed                         supplied

meq/l                                      oz per 1,000 gal                                ppm

0.10                                                   1.3                                           4

0.25                                                   3.3                                         10

0.50                                                   6.7                                         20

1.00                                                 13.4                                         39

 

Decrease Alkalinity of Irrigation Water

The values indicate the amount of acid to inject to neutralize approximately 80% of the alkalinity and drop pH to approximately 5.8, and the resulting concentrations of nutrients provided.

                                         Fluid ounce of acid per          Nutrient Concentration

                                        1000 gals of water added      from one fl oz. of acid per

Acid Used                     for each meq of alkalinitya        1000 gallons of waterb

Nitric acid (67%)                          6.78 fl oz.                               1.64 ppm N

Phosphoric acid (75%)                  8.30 fl oz.                               2.88 ppm P

Sulfuric acid (35%)                      11.00 fl oz.                              1.14 ppm S

a -    Add this amount of acid to 1,000 gallons of water for each meq of alkalinity present.  For, example, if your water has an alkalinity of 3 meq/l and you use sulfuric acid, you need to add 33 fl oz of 35% sulfuric acid per 1,000 gallons of water (11 fl oz/meq x 3 meq/l = 33 fl oz).

b - In the above example, the acidification treatment would supply 38 ppm S at each irrigation (33 f. oz x 1.14 ppm S/fl oz = 38 ppm S).