The special details of cultivation for each of the medicinal plants
mentioned are given under the discussion of the individual species.
Suggestions which are of general application, however, are here brought
together, in order to avoid unnecessary duplication.
_Propagation._--A number of the species considered later can be grown
easily from seed, but others are best propagated from cuttings or
by division. Many wild medicinal plants are much more difficult to
propagate from seeds than the species commonly grown in gardens.
Likewise, some of the species now grown abroad and suitable for
cultivation in this country are not easily propagated and require
special conditions if good results are to be realized.
[Illustration: Fig. 1.--Lath shed affording partial shade, especially
well suited for growing woodland plants.]
Seeds of the better-known varieties of medicinal plants are regularly
listed in the catalogues of numerous seed houses, and those which are
less common can usually be obtained from dealers who make a specialty
of one or more of these species. Plants can frequently be obtained from
nurseries or from dealers in hardy ornamentals. The catalogues of a
number of dealers should be consulted and the varieties for propagation
carefully selected. In ordering, the medicinal variety should always be
called for, since many of the related ornamental forms which are listed
are of doubtful, if any, medicinal value.
_Sowing the seed._--A relatively small number of medicinal plants can
be satisfactorily grown from seed sown in the field. In many cases this
method is quite uncertain and with some plants wholly inadvisable.
In order to insure a good stand of thrifty plants it is frequently
necessary to make the sowings in a greenhouse, hotbed, or coldframe
and at a suitable time transplant the seedlings to the field. Much
information on seed germination, hotbeds, and coldframes can be gained
by consulting Farmers' Bulletins 934, 937, and 1044, entitled,
respectively, "Home Gardening in the South," "The Farm Garden, in the
North," and "The City Home Garden."[1]
[1] These publications can be obtained free of charge upon application
to the Secretary of Agriculture, Washington, D. C.
The preparation of the soil is of prime importance, whether the sowing
of the seed is made in the open or under cover. Many seeds, especially
those which are very small, do not germinate well in heavy soils or in
those which are cloddy and coarse in texture. A seed bed prepared by
thoroughly mixing equal parts of garden soil, leaf mold, well-rotted
manure, and clean sand will be suitable for the germination of most
seeds.
The depth of sowing is largely governed by the size of the seeds and
the character of the soil. In general, the smaller the seed the less
the depth of sowing. Seed should be covered more deeply in light
sandy soil than in heavy clay soil. Fall-sown seeds also require a
greater depth of covering than those sown in the spring. The exact
quantity of seed which should be used for sowing a given area can not
be definitely stated. The same kind of seed will be found to vary
widely in its power to germinate; hence, the percentage of germination
should be ascertained in advance of sowing and the quantity regulated
accordingly. In general, the heavier the soil the larger the quantity
of seed required. If the plants are to be thinned out or transplanted,
or if they are especially subject to the attacks of insects, the free
use of seed is usually advisable.
When plantings are made in open ground it is preferable to sow the
seed in rows or drills, in order that cultivation of the soil may be
possible. A shallow furrow may be opened with a rake or hand hoe and
the seed sown by hand. The rake or hoe may then be used to cover the
seed with the required depth of soil. It is much more satisfactory
to use seed drills, such as are commonly used by market gardeners,
than to sow by hand, since with the drill the depth of sowing is more
uniform and the soil is compacted over the seeds, thus favoring good
germination. The distance between the rows is determined in part by the
size which the plants attain at maturity, but depends chiefly upon the
method of cultivation to be used. A spacing of 9 to 16 inches between
the rows will readily permit hand cultivation, but the rows should be
about 3 feet apart if horse-drawn implements are employed.
_Cultivation._--There are no set rules for the cultivation of medicinal
plants, and the grower's experience with other plants must be relied
upon as a guide in many of the details of cultivation. As a general
rule, the soil should be worked with the hoe or cultivator at frequent
intervals and kept free from weeds. It is a good practice to cultivate
after a hard rain as soon as the ground is sufficiently dry. During
dry, hot weather loss of moisture from the soil will be diminished by
frequent shallow cultivations.