SEED SOWING 
133 
of onions is very slow and tedious, and therefore great 
care should be taken to sow just the right amount of 
seed. (8) Ravages of insects. Insects are usually very 
destructive to certain plants, as melons and cucumbers, 
and by using plenty of seed there will be greater cer- 
tainty of saving enough plants to make a satisfactory 
stand. It generally pays to use seed freely and to thin 
when necessary. 
193. Thinning. — This is an important operation in 
growing many garden crops, and it is often practiced in 
starting plants under glass, but more frequently in open- 
ground culture. Thinning is a process of selection; the 
weakest plants should be discarded, and only the most 
vigorous left to mature. This is one of the strongest 
arguments for thinning. Thinning secures a uniform 
stand. Because the operation is tedious and expensive 
successful gardeners endeavor to avoid it as much as 
possible by the even distribution of the proper quantity 
of seed. 
194. Depth of sowing. — 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 cover- 
ing 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, be- 
cause 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 
