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PLANT PROPAGATION
Bert T. Swanson and Peter D. Ascher
Propagation is the genesis of all plants in the nursery of this mistake is called a mutation or sport. When the
industry. Propagation is an amazing, intriguing and in sport appears useful or novel, it can be asexually
some cases a very complicated process. Without propagated as a new cultivar.
propagation there would be no new plants and in fact
there would be no plants to plant or to sell. In the Asexual propagation is important because it allows for
overall scheme of the nursery profession, propagation perpetuation of a particular plant without change.
places #1 relative to the initial investment in a nursery Other reasons for asexual propagation include
enterprise. It is the Propagation System that feeds the shortening the time to flowering or fruiting, physically
Field System, the Container System, their Product altering the shape, size, or habit of the plant,
Systems which in turn provide a Marketable Product, constructing individuals consisting of more than one
and finally a Return on Investment. This Product Flow cultivar or sex, increasing disease or insect resistance,
System is shown in Figure 1. Obviously each and creating virus-free stock.
enterprise is not involved in each system, however,
without the Propagation System, the other systems Propagation Records
could not function. Although propagation may begin with a particular
plant using techniques from associates or references,
Reproduction of valuable plants is the foundation of eventually personal experience with specific material
the nursery industry. Plants are propagated in will enable the propagator to develop individual and
fundamentally different approaches: sexually, from unique techniques. These detailed modifications in
seeds, or asexually, from cuttings, apomictic seeds, procedures separate the average propagator from the
divisions, suckers, runners, rhizomes, layering, really skilled propagator. Development of “individual
budding, and grafting. Not only do these propagation tricks of the trade” depends on accurate records.
techniques vary in complexity and time required, they Experience gained each season must be used for
also differ significantly in the products produced from propagation decisions in subsequent years.
each technique.
A journal may be the easiest way to record procedures
Sexual propagation allows for recombination of that work. Record all procedures as the actual work is
parental characters and results in individuals that differ being accomplished, rather than at the end of the day
from each other and the parents. In many trees and or week. Details are easily lost over even a short time.
shrubs, differences between seedlings are unimportant, Information essential for a propagation procedural
provided that the plants fulfill the desired function. In journal includes the following:
some cases, particularly those involving mass plantings
of a single species over large areas, variations between 1. Date propagation began.
seedlings may offer some protection against
catastrophic effects of diseases or pests. Sexual 2. Name of plant (common and scientific).
reproduction is also the basis for plant improvement.
Plant breeders depend on the variation generated from 3. Source and type of propagating material.
recombination of parental traits for selection of new
plants, new traits, or new characteristics of plants. 4. Propagation medium used.
Asexual propagation, which is reproduction without 5. Hormones or growth regulators used including full
parental crossing, usually produces plants which are chemical name and the rates of application.
carbon copies of the parent or stock plant. The only
time that the plant produced would not be the same as 6. Environmental treatments applied.
the stock plant is when the genetic information in a cell
is not copied correctly during cell division. The result
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7. Pesticide treatments applied. Products such as peat, coconut coir, perlite,
vermiculite, rice hulls or various combinations of these
8. Temperature and light conditions. and other products provide these requirements. Seeds
germinate best in a seed flat or bedding plant pack that
9. Misting settings in detail. is approximately two to 2½ inches deep with drainage
holes. For maximum success, fill the flat or pack with
10. Date propagation completed. medium, place seeds directly on top of the medium
rather than pushing them down into the medium. Then
11. Percent success or failure and reasons therefore. cover the seeds with 1/8 to 1/4 inch of sand,
vermiculite, sphagnum moss, or other appropriate
12. Percent survival and vigor of plants after covering. The vermiculite will allow some light to
transplanting. reach the seed while keeping moisture available to the
seed. However, vermiculite may hold too much water
Merely recording procedures in a journal is not at the medium surface wherein fungus gnats can
sufficient. After the propagating season, summarize all become a problem. Commercial growers use a similar
journal entries to develop a protocol for the next process, however, they use plug trays. Plug
propagating season. File each protocol by plant name germination trays are difficult to manage for
for easy future access. homeowners. The small volume of media in the
individual plug cells incur rapid pH and moisture
The final step in record keeping is to update the changes that are difficult if not impossible for the
protocols each season, using information from the average homeowner to manage. Most seeds will
most current journal. Several years of experience are germinate well at a media temperature of 68-75F°.
often the best source for propagation success. There are some species that will need cooler or warmer
temperatures. To optimize germination, check a
Sexual Propagation grower’s recommendations or a seed germination
Some plants are most economically propagated from reference such as Seeds of Woody Plants in the United
seeds; others can only be propagated from seeds. A States or the Ball Red Book for specific crop
seed is a ripened ovule containing an immature plant recommendations.
and, usually, stored food reserves. Germination of a
seed is a process beginning with imbibition, or the Because the seed-germination medium must be
uptake of water, and the mobilization of food reserves. constantly moist, evaporative cooling from the medium
With the swelling associated with imbibition, cells may lower the temperature of the medium. Cool or
divide and the root tip or radicle emerges through the cold germination conditions slow the germination
seed coat. For seeds that exhibit epigeal germination, process and favor the development of fungi causing
that is, the seed leaves or cotyledons, appear above damping off, a major stem girdling disease of
ground, the stem between the root and cotyledons is germinating seedlings. Adding extra heat to the
called the hypocotyl, and forms a hook, pulling the germination medium by adding bottom heat, not only
cotyledons up. If the seed has only one cotyledon, speeds germination and early seedling development, it
which is called a monocot rather than a dicot, the also retards damping off. Other controls for damping
cotyledon itself forms a hook and penetrates the soil off include the use of sphagnum moss, not sphagnum
surface. On the other hand, the cotyledon or peat, as a light covering over the germination medium;
cotyledons of some seeds remain below the soil seed treatment with fungicides; lowering the pH of the
surface. These seeds exhibit hypogeal germination. germination medium; and fungicidal drenches after
germination. Sphagnum moss retards damping off
The general requirements for seed germination include because it is fungistatic. This means it will prevent
moisture, proper temperature, appropriate light or fungal growth, but not kill it.
darkness, and gas exchange. Species differ in response
to light during germination, some being stimulated, Seed Dormancy – Some plants have dormant seeds.
others inhibited. These seeds will germinate slowly and irregularly or
not at all, when placed under the warm, moist
Germination media used for seed germination must conditions required for germination of non-dormant
provide the appropriate balance of drainage, aeration seeds. Seed dormancy may be due to one or a
and moisture availability to the developing seedling. combination of three causes:
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1. A hard, impervious seed coat. specific temperature and moisture regimes for each
species.
2. An immature embryo.
Immature Embryo – Seeds of some plants, especially
3. An internal chemical inhibition. woody plants, may be released from the parent plant
with underdeveloped embryos. Generally, these seeds
Hard Seed Coat – To determine whether seeds have an need warm, moist conditions to finish embryo
impervious seed coat, soak them overnight in warm development before they will germinate. Immature
water. If the seeds do not swell, the seed coat may be embryos will complete development if seeds are sown
hard and impervious. These seeds require in seed flats out of doors in late summer or early fall.
scarification, which is the breaking or dissolving of the Direct sowing in the field is not advisable since it is
hard seed coat. An obvious method of breaking a difficult, if not impossible, to weed without disturbing
hard seed coat is by physical abrasion. With large the seeds. In using a heated structure, seeds should be
seeds, a file or sandpaper may prove satisfactory, but, sown in a seed flat, watered well, and covered to
with small seeds, some other method must be used. In prevent drying. Many seeds with immature embryos
nature, acid scarification occurs in the digestive tract of also exhibit an internal dormancy and must be
animals. Seeds of any size can be scarified with strong subjected to conditions to break that dormancy after
acids, such as sulfuric acid. Handling a strong acid is completion of embryo development.
extremely dangerous and disposing of the acid after
use may be difficult. When diluting sulfuric acid, Internal Chemical Inhibition – Seeds of many plants
always add acid slowly to water, never add water to from temperate regions of the world are dormant when
acid! Many seeds with hard seed coats can be released from the parent plant because of chemical
scarified more safely with household bleach. Usually conditions inside the seed or associated structures.
several hours in a 1:1 mixture of bleach and water Occasionally, these chemicals can be washed or
dissolves the seed coat. Timing is important with both leached from the seed, but a more reliable method for
acid and bleach, because once the hard seed coat is overcoming internal dormancy is by stratification
dissolved, the embryo is exposed and it could be killed. which usually consists of cool and moist storage
conditions. Cool or cold, dry storage will not work, as
Other natural means of scarification are alternate seeds must be imbibed with water to perceive the cold.
freezing and thawing, or exposure to high The best temperatures are above freezing, in the range
temperatures. Low temperatures cause the seed to of 33 to 40ºF., although light freezing usually will not
contract and high temperatures cause the seed to harm the seeds. The required cool, moist treatment can
expand, both leading to rupture of the seed coat. be given naturally by sowing the seeds in the fall in a
Natural freeze-thaw scarification will occur if seeds are seed bed, cold frame or hot bed, or by placing covered
sown out of doors in the fall, either in the field or in a seed flats out of doors in the fall or late winter. Seed
cold frame. Alternatively, seed flats may be covered flats, covered with plastic to prevent drying, can also
with plastic to retard drying and placed out of doors in be chilled in any refrigerator or cold storage unit. To
fall or late winter or exposed to several freezing and save space, all but the smallest seeds can be placed in
thawing cycles, using a home freezer. moist sand or peat in plastic bags in a refrigerator,
High-temperature scarification can be accomplished by rather than sown in seed flats. The practice of
covering the seeds with boiling water for a short period alternating layers of moist sand or peat with layers of
of time. To prevent small seeds from being damaged seeds for cool, moist storage gave rise to the term
in this process, quickly lower the temperature by stratification in the nursery trade. The length of
adding cold water. Allow the seeds to remain in this stratification necessary to overcome internal dormancy
warm water overnight and then check for swelling. depends on the species and varies widely between
Remove and sow any that have imbibed water. Repeat species. Although generalization is difficult, six weeks
the boiling water treatment for those seeds which is often the minimum time required, and many species
failed to swell. Seeds which swell, but fail to require 12 to 16 or more weeks of stratification. Some
germinate, may have an immature embryo and/or species germinate only after a cold-warm-cold-warm
internal dormancy in addition to a hard seed coat, and cycle. These seeds will germinate the second year
they may need to be stratified. Stratification provides after fall sowing out of doors.
the proper conditions for the pre-germination
physiological maturation of a seed. This occurs under
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