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.

 

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.

 

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 (30-45^o) 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 T-bud inverted T- bud I-bud patch bud