Propagation involving regenerative processes, such as the formation of new roots or shoots, immediately demands some form of environmental support until the new plants become independent. This also applies to grafts and much seed propagation.
The degree of care needed depends on the species of plant and the mode of propagation used. Easily rooted plants, for example propagated by hardwood cuttings outdoors in winter, require minimal care, in contrast with leafy cuttings taken in summer from a difficult-to-root plant - these will need a closely regulated environment.
In cooler climates, favorable conditions can often only be achieved under cover, whether it be in the home, conservatory or greenhouse, to extend the growing season or increase tender plants. For outdoor propagation, cold frames, cloches or nursery beds offer a degree of shelter. In warmer regions, windbreaks, shading structures and irrigation systems may be required. Propagating plants away from their natural or adapted habitat makes them vulnerable to attacks from pests and diseases so the propagation area should be kept as clean as possible.
Generally, seeds require water, warmth, air (oxygen) and sometimes light to germinate; seedlings and vegetative material need water, warmth, air (oxygen, carbon dioxide), light and sometimes nutrients to grow.
THE AERIAL ENVIRONMENT
The humidity of the air affects the rate at which plants transpire, allowing water to evaporate from leaf pores.
The more humid the air, the less the plants transpire. This is a critical issue for none rooted leafy cuttings which in spring and summer need an atmosphere of 98-100 per cent humidity, and about 90 per cent in winter, to prevent wilting. Wilting cuttings have a reduced ability to regenerate, form callus tissue at the base, or subsequently develop roots.
Cuttings absorb moisture through their cut bases more quickly than through leaves, but once callus tissue forms (in 3-7 days) water can only be taken in by the leaves. The 'reduced transpiration can stress cuttings, resulting in leaf-drop, so humidity is essential for the survival of the cuttings.
Leafy cuttings obtain energy for rooting by photosynthesis; for this to occur, light, water and carbon dioxide are needed. Long summer days assist with this process, but intense light in summer overheats the air, which in turn causes excessive transpiration and s to cuttings. Shading to enable indirect light (irradiance) aids rooting in a wide range of plants. Photosynthesis is then restricted, but can be maximized by ventilating the propagation area to ensure a normal atmospheric balance. Ventilation must be regulated to avoid excessive loss of humidity.
There are two factors to be considered in propagation: the aerial environment and growing medium.
Elements in each must be balanced to encourage growth.
• Humidity: to prevent moisture loss by transpiration
• Light: to allow photosynthesis without scorching.
• Temperature: appropriate to plant.
• Air quality: oxygen for respiration and carbon dioxide for Photosynthesis.
• Moisture level: to encourage roots and for photosynthesis.
• Temperature: to encourage growth.
• Aeration: sufficient oxygen for growth and to avoid diseases.
• PH (acidity and alkalinity): usually acid, but appropriate to the plant.
• Nutrient level: low until roots establish then increased for steady growth.
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