The most common method of starting early plants in the North is by
means of a hotbed. The hotbed consists of an inclosure covered with
sash and supplied with some form of heat, usually fermenting stable
manure, to keep the plants warm and in a growing condition. As a rule,
the hotbed should not be placed within the garden inclosure, but near
some frequently used path or building where it can receive attention
without interfering with other work. The hotbed should always face to
the south, and the south side of either a dwelling, barn, tight board
fence, hedge, or anything affording a similar protection, will furnish
a good location. The hotbed should be started in February or early in
March, in order that such plants as the tomato and early cabbage may be
well grown in time to plant in the open ground. There are two or three
forms of hotbeds that are worthy of use.
A temporary hotbed, such as would ordinarily be employed on the farm,
is easily constructed by the use of manure from the horse stable as a
means of furnishing the heat. Select a well-drained location, where the
bed will be sheltered, shake out the manure into a broad, flat heap,
and thoroughly compact it by tramping. The manure heap should be 8 or
9 feet wide, 18 to 24 inches deep when compacted, and of any desired
length, according to the number of sash to be employed. The manure for
hotbed purposes should contain sufficient litter, such as leaves or
straw, to prevent its packing soggy, and should spring slightly when
trodden upon. After the manure has been properly tramped and leveled,
the frames to support the sash are placed in position facing toward
the south. These frames are generally made to carry 4 standard hotbed
sash, and the front board should be 4 to 6 inches lower than the back,
in order that water will drain from the glass. Three to five inches
of good garden loam or specially prepared soil is spread evenly over
the area inclosed by the frame, the sash put on, and the bed allowed
to heat. At first the temperature of the bed will run quite high, but
no seeds should be planted until the soil temperature falls to 80° F.,
which will be in about three days. In most farmhouses enough heat is
wasted throughout the winter to sustain a small hothouse to say nothing
of a hotbed.
Hotbeds having more or less permanence may be so constructed as to
be heated either with fermenting manure, a stove, a brick flue, or
by means of radiating pipes supplied with steam or hot water from
a dwelling or other heating plant. For a permanent bed in which
fermenting manure is to supply the heat, a pit 24 to 30 inches in depth
should be provided. The sides and ends of the pit may be supported by
brick walls or by a lining of 2-inch plank held in place by stakes.
Standard hotbed sash are 3 by 6 feet in size, and are usually
constructed of white pine or cypress. As a rule, hotbed sash can be
purchased cheaper than they can be made locally, and are on sale by
seedsmen and dealers in garden supplies. In the colder parts of the
country, in addition to glazed sash either board shutters, straw mats,
burlap, or old carpet will be required as a covering during cold
nights. It is also desirable to have a supply of straw or loose manure
on hand to throw over the bed in case of extremely cold weather.
During bright days the hotbed will heat very quickly from the sunshine
on the glass and it will be necessary to ventilate during the early
morning by slightly raising the sash on the opposite side from the
wind. Care should be taken in ventilating to protect the plants from a
draft of cold air. Toward evening the sash should be closed in order
that the bed may become sufficiently warm before nightfall. Hotbeds
should be watered on bright days and in the morning only. Watering in
the evening or on cloudy days will have a tendency to chill the bed and
increase the danger from freezing. After watering, the bed should be
well ventilated to dry the foliage of the plants and the surface of the
soil and prevent the plants being lost by damping-off fungus or mildew.