Horticulture Principles and Practices

seeds may be treated in this way before planting. Pelleting makes planting easier and
spacing more precise. New methods of preparing seeds for planting are being investigated.
For uniform germination and establishment of a crop, planting of pregerminated
seeds is being investigated. Recently, sprouted seeds have been suspended in a protective
gel or drilled with some water, a method called fluid drilling.
9.12 ENVIRONMENTAL CONDITIONS FOR SEED GERMINATION
Germination involves physiological and biochemical processes. The belowground environmental
conditions (Chapter 4) must be adequate for seeds to germinate. The critical
factors are as follows:
1. Moisture. Seeds must imbibe moisture to a certain degree for the germination
process to be initiated. Moisture is needed to initiate the enzymatic breakdown of
food reserves. The critical degree of imbibition differs among species. For
example, whereas soybean needs to imbibe about 50 percent of its weight before
germination, sorghum requires only about one-third of its weight. Horticultural
plants that germinate best under conditions of high moisture include beet, celery,
and lettuce. When raising seedlings in flats, a glass plate may be used to cover
the flat to prevent moisture loss through evaporation (Figure 9–4). Similarly, the
flat may be placed in a plastic bag to accomplish the same purpose (Figure 9–5).
Although moisture is critical to germination, excessive moisture encourages
rotting and other diseases.
Sheet of glass FIGURE 9–4 Seed germination:
(a) using a flat covered with a
sheet of glass to retain humidity;
(b) using a plastic cover over a flat.
(Source: For (b) George Acquaah)
(a)
Flat containing
recently planted seed
(b)
9.12 Environmental Conditions for Seed Germination 299