28 BULLETIN 479, U. S. DEPARTMENT OF AGRICULTURE. 
COVERING THE SEED. 
In some cases the seed are covered by the drill itself. In others 
the covering must be a separate operation. It is ordinarily accom- 
plished by sifting sand or soil over the beds through a screen of 
about one-fourth-inch mesh. One man can easily cover from forty to 
fifty 4 by 12 foot beds per day of 8 hours. Skill is required to cover 
the seed to a uniform depth so as to insure equable conditions and 
relatively even germination. There is a tendency to distribute the 
soil too deep over the center of the beds and too shallow along the 
edges. One method of covering requires a frame and planing board 
similar to those shown in figure 2. If broadcast sowing is prac- 
ticed, the frame need not be removed from the time the bed is first 
leveled until covering has been completed. The soil used in covering 
is sifted over the seed bed, and a planing board, narrower by the 
depth to which it is desired to cover the seed than the one used in 
sowing, is then drawn along the frame. By this means the seed is 
covered at a very even depth. Some other methods of covering are 
followed. Soil is shaken off the blade of a shovel over the seed or 
scattered by hand. In drill beds sown by hand the seed is sometimes 
covered with the back of a rake or, as in one of the most successful 
Forest Service nurseries, by drawing the finger through the soil 
between the rows, thus closing the open drills. 
The depth of covering most suitable for any one species varies 
uccording to differences in soil and nursery practice. Even under 
very constant conditions some latitude may be exercised without 
danger of seriously affecting the germination of the seed or their 
subsequent pushing through the covering. If heavy clay soil is 
used as a cover, the maximum depth permissible can not be so great 
as if a lighter sandy soil is used because the seedlings experience 
greater difficulty in breaking through. By reason of their greater 
size and strength seedlings from large seed can more readily push 
through a heavy covering than seedlings from small seed. There- 
fore, the former can safely be covered more deeply than the latter. 
Less work is necessary to put on a light cover than a heavy one, 
and the seedlings appear sooner and more evenly in the beds. It is 
true that with a shallow covering there is greater probability of the 
soil becoming dry to the depth of the seeds, resulting in damage 
to them; but this possibility can not be avoided by any depth of 
covering consistent with good nursery practice. Danger of this 
nature must be guarded against by frequent watering or by pro- 
tecting the seed beds. ^Vhen moisture conditions in the seed beds 
can be controlled, Forest Service experience indicates strongly that 
shallow coverings are preferable, from one-eighth inch with smaller 
classes of seed, such as spruce, the Thujas, larch, lodgepole pine, and 
