Hulled seed makes up a large percentage of the sweet-clover seed sown.
The germination of hulled seed varies considerably, although ordinarily
it is higher than that of unhulled seed. Seeding experiments conducted
at Arlington, Va., with seed which germinated 80 per cent show clearly
that seed which germinates well should not be sown during the winter
months in those sections of the country where midwinter thaws are
likely to occur, and especially in sections south of the latitude of
southern Ohio. In these experiments seed was sown during each month
of the winter. Good stands were obtained only on those plats which
were sown in the latter part of February and during March and April.
At least 75 per cent of the seed sown during November, December, and
January germinated on warm days during winter thaws and was killed
by later cold weather. Notwithstanding the fact that sweet-clover
seedlings will endure fairly low temperatures, seed germinating more
than 50 per cent should not be sown during the winter months, and
preferably not more than a week previous to the average date for the
last severe freeze.
No data have been secured on winter seeding in those portions of the
United States where open winters do not occur. It is probable that in
those sections the winters are sufficiently cold to prevent germination
before spring. Good results may be obtained by winter seeding, but as
usually no trouble is experienced in those sections in obtaining a
stand by seeding as soon as the soil can be worked in the spring, it
is strongly recommended that seeding be done with hulled seed, which
germinates well at this time of the year.
Many excellent stands have been obtained by seeding late in the spring,
but in most sections seeding at this time is not as certain to produce
a good stand as earlier seeding. Late spring seeding may be preferable
when the ground is weedy and the clover is to be seeded without nurse
crop. Under these circumstances a crop of weeds may be destroyed before
seeding.
Very good success has been obtained in the Southern and Central States,
and in some of the Northern States, by seeding sweet clover in the
late summer or early autumn. When there is sufficient moisture in the
soil for germination and when good seed is used, better stands have
been obtained by seeding about eight weeks before severe frosts are
to be expected than from spring sowing. This is particularly true in
regions where late spring droughts or severe summer droughts are likely
to occur. Seeding at this time may be done after an early crop has
been harvested and when weeds are not likely to be troublesome. Plants
from fall seeding mature from 10 days to two weeks later the following
season than plants from spring sowing of the same year. The later time
of maturing is an advantage, in that the plants will be ready to cut
during better haying weather. The root growth is not as large from fall
seeding as from spring seeding, and therefore not quite as much humus
is added to the soil. Late fall seedings are very likely to be injured
from heaving on wet clay soils.