The successful propagation of new plants from seeds depends on careful attention to all of the production factors. Should any one factor be limiting, the survival or quality of the plants can be affected. The factors of good production are:
• good quality seed
• correct propagation medium
• correct planting techniques
• appropriate lighting
• proper watering
• good drainage
• proper temperature
• adequate nutrients
The attributes of high-quality seed and the features of good propagation media have been discussed.
Planting techniques for seeds vary depending on whether the species are herbaceous or woody, and whether they are to be transplanted after germination or will be grown at the planting site.
Procedure for Planting Seeds of Herbaceous Greenhouse Crops
1. Fill greenhouse flats with a propagating medium that has been pasteurized and is well-aerated, well-drained, and fertile.
2. Tamp and firm the medium to drive out air pockets. Leave about one-half inch of space at the top of the flat to allow for watering.
3. Plant the seeds in furrows or in holes made with a pegged board. Tiny seeds may be broadcast over the surface. The seeds may be covered with additional propagating medium. Shaking the medium through a wide screen sieve will ensure that the seeds are covered evenly.
4. If the seeds are large enough so that they will not be washed away, the flats can be watered from above (Figure 14-2). For fine seeds, the flats should be immersed in water before seeding. The planted seeds should be kept moist for rapid germination, yet not so moist that damping-off disease becomes established. Moisture may be applied by hand-watering or by use of a mist system. Moisture loss can be reduced by covering the flat with glass or transparent plastic for a portion of the day. Care must be taken to ensure that the seedlings do not remain too wet at night.
5. A germination temperature of 70° to 75° F is suitable for most greenhouse plants. Tropical plants may require higher temperatures. Plants should not be allowed to overheat.
6. After germination, reduce the temperature to between 65° and 70° F and maintain moderate light intensities. A soil drench to guard against damping-off disease is advisable. A slight reduction of water to a point that the new roots are moist while the surface is moderately dry will also aid in control of damping-off.
7. After two to four true leaves, not the seed leaves (cotyledons), have formed, transplant the seedlings to allow healthy growth to continue. If conditions at the transplant site are more stressful than at the germination site (as when seedlings are moved from greenhouse to field conditions), a hardening-off period is needed. Hardening-off occurs when reduced temperature and water cause carbohydrates to accumulate in the plant tissue, allowing it to survive transplant shock. The hardening-off process is described in more detail later in this chapter.
Procedure for Planting Seeds of Woody Crops for Container Production
1. Following any preconditioning that may be necessary, the seeds can be planted as in the previous procedure. The time required for germination may be considerably longer with woody crop seeds.
2. When the seedling roots have reached the bottom of the greenhouse flat, they should be pruned to promote branching.
3. Transplanting should follow, with each seedling moved from the germination flat to individual peat pots or other types of containers.
4. After roots extend an inch or so beyond the peat pot, they should be pruned off to encourage still more branching.
5. Set the plant into a production container for further growth.
Procedure for Planting Seeds Directly in the Ground
1. The in-ground planting site may vary from a nursery field for landscape plants to a hillside for a reforestation project. The soil should be prepared and conditioned as necessary to ensure that it is aerated, well-drained, fertile, reasonably weed-free, and of the correct texture. It may be necessary to work the soil with a rototiller or larger piece of agricultural equipment. There should be no large clods. Additions of organic matter, mixed well into the soil by the tiller, will help ensure the uniform size of the soil aggregates. A medium, loamy texture is ideal for seeding.
2. Seeds should be preconditioned to prepare them for planting. Certain species can be planted in the fall and after-ripened naturally in the soil. They will then germinate in the spring. Other species will germinate more uniformly if preconditioned by the grower before planting.
3. Seeds can be treated before planting to protect against damping – off, insects, birds, and rodents.
4. The seedbed will benefit by application of both preemergence and postemergence herbicides during production of the seedlings, which may extend over several years. Otherwise, the seedlings will suffer from competition with weeds for light, nutrients, and space to grow.
5. The seeds may be planted either by hand or by machine. The depth of planting will vary with the species. Two or three times the diameter of the seed is usually a satisfactory depth.
figure 14-2. Moisture can be applied to seeds from above as long as seeds are not too fine. (Delmar/Cengage Learning)
6. A mulch should be applied to shade the new seeding and aid water retention. The mulch also reduces the force of water on the new seeds and helps maintain their spacing. Lightweight organic mulches work best, but additional nitrogen should be applied to compensate for that tied up by microbes during the decomposition of the mulching.
7. The new seeding, if in a nursery seedbed, should be shaded. Whether in a seedbed or unshaded nursery row, it should be kept moist. Temperature extremes and drastic changes should be avoided.
8. The plants may remain in the seedbed or nursery row for a season or more before being transplanted.