There are no infallible rules to determine the proper depth for sowing. Certain writers have advocated the regulation of soil covering by the diameter of the seed; that is, by making the covering two, three or four times the diameter of the seed. Such rules may be of some value when sowing in the greenhouse or hotbed, where moisture and soil conditions are under control, but they are likely to be misleading when applied to field conditions. The size of the seed should be considered, and also the character of the soil. In light, sandy soils the depth might be several times as great as in heavy soils. Summer and early fall sowings require greater covering than early spring sowings, because the surface layer of soil is drier, and it is necessary to place seed at a greater depth to secure the necessary amount of moisture. Some of the smallest seeds, as celery, are often merely pressed into the soil. A very slight covering is sufficient for many seeds when the best conditions are provided. The reader should consult the chapter on the culture of the various classes of vegetables to obtain more definite information on the proper depths for planting.
The soaking of seeds before sowing is of doubtful value. It may be the means of hastening germination a few days, although sowing earlier will accomplish the same purpose. When plants are killed by frost and it becomes necessary to make another sowing a slight gain will be made by soaking the seed. Most growers, however, never soak any kind of seed before sowing.