Conditions required for successful asexual plant propagation

Tools used

All tools used for dividing or cutting plant material into sections should be sharp and clean because:

• clean cuts heal faster
• less disease will enter a cleanly cut surface
• sharp tools cut cleanly and don’t tear or crush the plant tissue. Damaged tissue allows disease to enter the wound
• clean tools transfer fewer disease organisms such as bacteria and viruses from one plant to another.

Environmental conditions

To have success with asexual plant propagation the following environmental conditions should be provided.

                                                                       

Environmental condition	Reason provided
A controlled (warm and humid) environment	Prevents water loss from transpiration, especially for softwood and leaf cuttings.
Air circulation	Air is needed around developing roots and shoots to stop disease and rotting.
Time of year has suitable environmental conditions for the type of propagation	Ideal air and soil temperature and light levels available.
Hygienic conditions including clean containers, tools and growing media	To prevent disease.       Fungicides and insecticides are used only if needed.
Media used:               is free   from pests, diseases, weed seed         will   hold water but excess water drains out	A balance of air and water around the developing roots so respiration can take place   and the cutting doesn’t dry out.       Clean media prevents disease.       Well-drained media prevents rotting.       Water should be available for developing roots.
Warm temperatures near the base of cuttings	Warm temperatures increase the rate of plant processes, therefore there is faster development of roots.
Light	Leaves on cuttings need light to carry out photosynthesis. This will give the cutting sugars that can be used for developing new roots and shoots.       Developing shoots need light to carry out photosynthesis.
Hardening off newly propagated plants	Weaning the plant material from a protected environment and hardening it off once new roots and shoots have developed so it becomes a self-supporting plant.

Biological conditions

To have success with plant propagation the following biological conditions should be provided:

• Buds must be present on each section of plant material used for propagation.
• Plant material from younger parent plants should be used as this is more likely to produce new roots and shoots.
• Current year’s growth should be used because it will produce roots faster from cuttings and layering than older plant material.
• Healthy good looking stock/parent plants free from virus diseases.
• Parent plants that have had good nutrition and water in the months before the cuttings are taken or the layering or division is carried out.
• Plant material used for propagation must be large enough to contain enough stored energy to sustain it while new roots and shoots grow.
• Plant hormones can be used to encourage root formation.
• The time of year the propagation takes place is suitable. This can determine if the plant material has enough stored sugars and therefore enough energy to produce new shoots and roots.

Key conditions required for successful asexual plant propagation

                                                                                               

Plant material	Method of propagation	Key conditions
Root tubers, stem tubers, corms, bulbs	Division	Healthy young plant material used.       Each piece of plant material will have a healthy bud.       Each piece of plant material should be large enough to have a food store to support the development of new roots and shoots.       The cut surface of the plant pieces should be left to dry in a warm airy place to seal the cut surface from diseases.       Cut pieces should be placed in clean, friable, well-drained loam or growing media that is kept moist (field capacity).       Plant the new plant in a hole twice the depth of the size of the piece of plant material.       Light is required once the shoots appear so the shoots can carry out photosynthesis.       Protect developing shoots from adverse environmental conditions, e.g. frost.       Time of year –propagate in early spring when plant material is still dormant but just before it is about to grow shoots.
Rhizomes (e.g. Bearded iris), fibrous crowns (e.g. herbaceous perennials such as Chrysanthemum)	Division	Healthy young plant material used.       Each piece of plant material must have a healthy bud.       Cut back leaf material to reduce water loss.       Remove old plant material.       Replant plant material at the same depth as the parent plant. If planted too deep, rhizome may rot or shoots may struggle to reach the soil surface.       Keep media moist and protect from adverse weather.       Time of year – propagate after flowering or when dormant.
Root or stem tuber or fibrous crown e.g. Chrysanthemum	Softwood cuttings	Healthy young plant shoots used.       Shoots 7–10 cm long.       Cut straight under a node – a node is more resistant to fungal rots than other parts of the stem. Cells at the node will divide and produce roots faster than in other parts of the stem.       Placed shoots in well-aerated media. Media is well-aerated to prevent rotting of the cutting and the media will be warmer.       Media used for the plant material should be friable, aerated, well drained, moist and warm (if appropriate). The higher the temperature around the plant material forming roots, the faster the chemical reactions and therefore the faster the root formation.       Provide cutting with high humidity to prevent water loss.       Provide warm temperatures at the base of the cutting to speed up root development in a disease free controlled environment (bottom heat 21°C).       Good light levels needed so the cutting can carry out photosynthesis.       Time of year – take cuttings late spring after the buds have started to shoot.
Offsets   and runners	Division	Replant healthy young offsets or rooted runners in a clean, friable, well-drained loam or growing media that is kept moist (field capacity).       Place offsets in a warm sheltered area.       Offsets from succulents need to be in a non-humid environment or they will rot.       Time of year – late spring, early summer.
Evergreen flowering shrubs	Semi hardwood stem cuttings or layering       Remember:               cuttings take less space than layering         cuttings produce more plants than layering         when layering the plant material is still provided with energy for growth from the parent plant therefore more likely to form roots successfully.	Use young vigorous non-flowering shoots.       Use young parent material where possible.       Shoots 7–10 cm long.       Cut large leaves in half to prevent water loss.       Cut straight under a node – a node is more resistant to fungal rots than other parts of the stem. Cells at the node will divide and produce roots faster than in other parts of the stem.       Media used for the plant material should be friable, aerated, well drained, moist and warm (if appropriate). The higher the temperature around the plant material forming roots the faster the chemical reactions and therefore the faster the root formation.       Rooting takes place during the growing season when layering.       Prevent the cuttings or parent plant drying out when layering.       Encourage fast rooting so it has taken place before the food supply in the stem is all   used up.       Prevent drying out and water loss.       Light is needed for photosynthesis.       Use rooting hormone.       Time of year – late spring, early summer or just after flowering.
Shrubs and trees and conifers	Hardwood cuttings	Wound the stem to stimulate root production.       Use plant rooting hormone.       Keep a cool environment for the tip to keep shoot growth to a minimum and prevent water loss and to stop energy reserves being used up before roots are developed.       Keep cutting warmer at the base to encourage faster root development.       Use heel cuttings for hard-to-root plants – the heel is more likely to produce roots and it is better protected against rot.       Cut under a node.       Deciduous cuttings should be a minimum of three nodes long.       Conifers – remove excess leaf material and cuttings 7–10 cm long.       Use rooting hormone.       Light is needed but not at levels that will dry out the cuttings.       Low humidity is needed to prevent rotting.       Time of year – dormant season, late autumn.
Pot plants	Leaf or softwood stem cuttings	The same conditions as for softwood wood cuttings.

Selection methods for Plant propagation

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Assessment

Complete HT1093Y1 after your teacher has returned your workbook with comments on your knowledge of plant propagation techniques

What's next?

1. Send your HT1093 bookwork to your teacher.
2. Send your divided potato pieces to your teacher
3. Complete HT1093Y1 after your teacher has returned your workbook with comments on your knowledge of plant propagation techniques.

Overseas students – DO NOT send plant material into New Zealand. Take photos of your practical work instead to email or post to your teacher.