Chapter 14Chapter 14

Techniques of Plant Techniques of Plant PropagationPropagation

Among all the crafts of ornamental Among all the crafts of ornamental horticulture, none exemplifies the horticulture, none exemplifies the

application of science to the profession application of science to the profession better than plant propagation.better than plant propagation.

To promote the initiation and development To promote the initiation and development of new roots on cuttings it is necessary to of new roots on cuttings it is necessary to create an environment for the cutting base create an environment for the cutting base that will:that will:– Support the cuttingSupport the cutting– Retain moisture uniformly Retain moisture uniformly – Drain away excess water uniformly Drain away excess water uniformly – Provide adequate aerationProvide adequate aeration– Not support weed seeds and other pests Not support weed seeds and other pests – Pasteurize easilyPasteurize easily

Materials that can be used in the Materials that can be used in the propagation medium:propagation medium:– Natural soilNatural soil

– SandSand

– Peat mossPeat moss

– Sphagnum moss Sphagnum moss

– perliteperlite

– VermiculiteVermiculite

– Fired clayFired clay

Peat moss

PerliteFired clayVermiculite

Steam pasteurization is used to eliminate Steam pasteurization is used to eliminate weeds seeds, nematodes, fungi, and other weeds seeds, nematodes, fungi, and other soil-borne plant pathogens.soil-borne plant pathogens.

Sand or peat moss are often added to the Sand or peat moss are often added to the growing medium to improve texture, growing medium to improve texture, moisture retention, and drainage.moisture retention, and drainage.

The propagation structure must possess The propagation structure must possess the following characteristics:the following characteristics:– Sufficient light to permit seed germination.Sufficient light to permit seed germination.– High humidity to reduce wilting of the cutting High humidity to reduce wilting of the cutting

until new roots can form and promote.until new roots can form and promote.– Warmth to accelerate germination or rooting.Warmth to accelerate germination or rooting.– Ventilation to reduce risk of disease once Ventilation to reduce risk of disease once

roots have been formed.roots have been formed. Certain areas of the greenhouse should be Certain areas of the greenhouse should be

designated as “propagation only” because designated as “propagation only” because it requires higher temperatures and higher it requires higher temperatures and higher humidity than typical greenhouse crops.humidity than typical greenhouse crops.

Seed suppliers usually provide the buyer Seed suppliers usually provide the buyer with information about the best time to with information about the best time to plant, any necessary treatments, and plant, any necessary treatments, and follow-up culture information.follow-up culture information.

Scarification is a process that breaks down Scarification is a process that breaks down tough seed coats by rubbing them with tough seed coats by rubbing them with sandpaper, soaking them in hot water or sandpaper, soaking them in hot water or acid, or by a similar process.acid, or by a similar process.

Common Scarification techniques:Common Scarification techniques:– SandpaperSandpaper– Hot water bathHot water bath– Sulfuric acid bathSulfuric acid bath

StratificationStratification- subjecting seeds to a required - subjecting seeds to a required period of low temperatures to induce growth.period of low temperatures to induce growth.

Double dormancyDouble dormancy- when plants require both - when plants require both scarification and stratification before they scarification and stratification before they germinate.germinate.

Factors of good propagation:Factors of good propagation:– Good quality seedGood quality seed– Correct propagation mediumCorrect propagation medium– Correct planting techniqueCorrect planting technique– Appropriate lightingAppropriate lighting– Proper wateringProper watering– Good drainage Good drainage – Proper temperatureProper temperature– Adequate nutrientsAdequate nutrients

Planting techniques vary depending on Planting techniques vary depending on whether they are herbaceous or woody, and whether they are herbaceous or woody, and whether they are to be transplanted or grown whether they are to be transplanted or grown at the planting site after germination.at the planting site after germination.

Plugs are seedlings that retain their Plugs are seedlings that retain their undisturbed root system within a core of undisturbed root system within a core of media.media.

In the production of ornamentals plugs are In the production of ornamentals plugs are mostly used for bedding plants.mostly used for bedding plants.

The majority of growers prefer to use plugs over The majority of growers prefer to use plugs over seed propagation techniques because:seed propagation techniques because:– Transplant shock and transplant times are reducedTransplant shock and transplant times are reduced– Plugs do not overcrowd as quickly and can be held Plugs do not overcrowd as quickly and can be held

longer for transplant.longer for transplant.– Seed sowing can be automated and there is no need Seed sowing can be automated and there is no need

to thin the seedlings after germination.to thin the seedlings after germination.– Plugs can be transplanted automatically.Plugs can be transplanted automatically.– Shorter production time allows more crops to be Shorter production time allows more crops to be

produced.produced.

If plugs are kept too long in a growth chamber If plugs are kept too long in a growth chamber they will stretch and overgrow. they will stretch and overgrow.

Cuttings are pieces of roots, leaves, or stems Cuttings are pieces of roots, leaves, or stems that are removed from the parent plant and that are removed from the parent plant and placed in an environment that promotes their placed in an environment that promotes their development into total plants.development into total plants.

Adventitious roots are initiated in herbaceous Adventitious roots are initiated in herbaceous plants from points just outside or between plants from points just outside or between vascular bundles. In woody plants they originate vascular bundles. In woody plants they originate next to and out from the vascular core. This is next to and out from the vascular core. This is significant in the “cutting process” because they significant in the “cutting process” because they may form after cuttings are taken or may be may form after cuttings are taken or may be performed but dormant.performed but dormant.

The best cuttings result from healthy stock The best cuttings result from healthy stock plants that contain adequate nitrogen and high plants that contain adequate nitrogen and high carbohydrate levels.carbohydrate levels.

Adventitious roots form more quickly on Adventitious roots form more quickly on stem cutting in the dark than in the light.stem cutting in the dark than in the light.

Stem or root cuttings taken from young Stem or root cuttings taken from young plants root more quickly than cuttings plants root more quickly than cuttings taken from older plants.taken from older plants.

When a species is difficult to root, better When a species is difficult to root, better results are usually obtained when results are usually obtained when vegetative growth is selected for the vegetative growth is selected for the cuttings.cuttings.

Factors the propagator must consider to protect Factors the propagator must consider to protect cuttings:cuttings:– Moisture – helps rootless cuttings absorb water. Moisture – helps rootless cuttings absorb water.

Usually created through a mist line.Usually created through a mist line.– Temperature – controls the rate of root and shoot Temperature – controls the rate of root and shoot

development.development.– Nutrition – influences the quality of cuttingsNutrition – influences the quality of cuttings– Acidity/Alkalinity – affects the number and quality of Acidity/Alkalinity – affects the number and quality of

cuttings.cuttings.– Light quality and intensity – high light intensity is Light quality and intensity – high light intensity is

important for good root production.important for good root production.– Oxygen content – oxygen is important for developing Oxygen content – oxygen is important for developing

plants.plants.

Hardening-off is important because the gradual Hardening-off is important because the gradual adaptation of plants to environmental conditions adaptation of plants to environmental conditions are more stressful than the present conditions.are more stressful than the present conditions.

Plant graftPlant graft – the union of parts from two or more – the union of parts from two or more plants into a single plant.plants into a single plant.

Much of the research into grafting has been Much of the research into grafting has been accomplished with citrus and fruit trees.accomplished with citrus and fruit trees.

While grafting can be done on both woody and While grafting can be done on both woody and herbaceous plants, it is most common to woody herbaceous plants, it is most common to woody plants.plants.

When the graft union is successful and the When the graft union is successful and the two different plants become one, it is two different plants become one, it is termed a compatible graft.termed a compatible graft.

Delayed incompatibilityDelayed incompatibility – a graft may be – a graft may be successful for years before suddenly successful for years before suddenly failing.failing.

Basic items required for grafting:Basic items required for grafting:– A knifeA knife– Tying materialsTying materials– Grafting waxGrafting wax

Budding is grafting using a single bud as the Budding is grafting using a single bud as the scion. To bud a plant, you remove a piece of scion. To bud a plant, you remove a piece of bark and replace it with a similarly sized piece of bark and replace it with a similarly sized piece of bark from another plant.bark from another plant.

Layering allows a new plant to form by creating Layering allows a new plant to form by creating a new plant that is still attached to the parent a new plant that is still attached to the parent plant by a stem, and is sometimes the chosen plant by a stem, and is sometimes the chosen method because a new plant can be separated method because a new plant can be separated after a root system develops.after a root system develops.

Compared to other methods of propagation, Compared to other methods of propagation, layering is usually slower, more expensive, and layering is usually slower, more expensive, and produces fewer plants per parent plant.produces fewer plants per parent plant.

Layering Layering

Simple layering – a dormant one year branch is bent Simple layering – a dormant one year branch is bent to the ground and covered with soil excepting the tip. to the ground and covered with soil excepting the tip. Roots will begin to form in the underground segment.Roots will begin to form in the underground segment.

Tip layering – a shoot from current growth is bent and Tip layering – a shoot from current growth is bent and covered. covered.

Mound layering – the parent plant is cut back to Mound layering – the parent plant is cut back to ground level to encourage shoot growth. The new ground level to encourage shoot growth. The new shoots are covered with soil. Each shoot makes a shoots are covered with soil. Each shoot makes a new plant.new plant.

Air layering – a young portion of stem is cut to induce Air layering – a young portion of stem is cut to induce root formation. Sphagnum moss is wrapped around root formation. Sphagnum moss is wrapped around the injured area, fastened on, and tied. When roots the injured area, fastened on, and tied. When roots form, the new plant is cut from the parent.form, the new plant is cut from the parent.

Serpentine layering – the branch being layered is Serpentine layering – the branch being layered is buries in many places, rising above the ground at buries in many places, rising above the ground at varying intervals.varying intervals.

The twentieth century lead the beginning of new The twentieth century lead the beginning of new propagation techniques known as tissue and propagation techniques known as tissue and organ culturing. These techniques permit the organ culturing. These techniques permit the reproduction of certain species from embryos, reproduction of certain species from embryos, pollen grains, shoots tips, or undifferentiated pollen grains, shoots tips, or undifferentiated plant tissue.plant tissue.

Totally sterile or aseptic conditions are essential Totally sterile or aseptic conditions are essential throughout the tissue and organ culturing throughout the tissue and organ culturing process.process.

Tissue and organ culturing are comparatively Tissue and organ culturing are comparatively new propagation techniques.new propagation techniques.