To promote the initiation and development of new roots on cuttings, it is necessary to create an environment for the cutting base that will
• support the cutting.
• retain moisture uniformly.
• drain away excess water uniformly.
• provide adequate aeration.
• not support weed seeds and other pests.
• pasteurize easily.
If seeds are the propagative unit, the medium must also be a source of nutrition for the developing embryo.
The propagating medium will usually contain one or more of the following materials:
• natural soil
• peat moss
• sphagnum moss
• fired clay
Natural soil is not commonly used for propagation unless mixed with quantities of coarser additives such as fired clay, sand, or perlite, to improve its drainage and aeration. If pure sand is used for propagation, it must not be too fine or drainage will be poor. The best sand to use is quartz sand, fairly coarse in texture. All the materials used as propagation media should be steam pasteurized before use to eliminate weed seeds, nematodes, fungi, and other soil-borne plant pathogens.
The time required for establishment of new plants will vary from a week to several months. With seed propagation, it will be necessary to transplant the newly rooted plants from the propagating medium to a medium that will provide the nutrients necessary for sustained growth. For nursery crops, the new plants may be set directly into the field. Greenhouse growers may choose to install the plants directly into greenhouse benches or into containers ranging in size from bushel baskets to small clay or peat pots.
Field soils and greenhouse bench soils must be of loamy texture and well drained. Both may require the addition of sand or peat moss for texture, moisture retention, and drainage. One of the soilless mixes may also be used. Tables 14-1 and 14-2 list the components of the (older) University of California and (newer) Cornell mixes that enjoy wide acceptance throughout the ornamental horticulture industry.
One Example of the University of California Soil Mix
Note: Additional nitrogen and potassium fertilizers will be needed as the plants grow.