Cold Frames and Hot Beds
COLD FRAMES
A cold frame is an outdoor growing "area" built without a bottom but
with a solid-sided frame of wood, cement or brick, and a removable
hinged top, glazed with glass, Fiberglas, or plastic. Cold frames
are invaluable. For instance, they take some of the spring bulge
from a greenhouse. Then there are plants such as delphiniums,
pansies, and Oriental poppies, to be planted in the frame in late
summer and kept there over winter. .
You can purchase material and build your own cold frame, buy
ready-fitted supplies from a greenhouse dealer and assemble it, or
you can buy a ready-made cold frame of wood or aluminum with plastic
"lights."
How to Build a Cold Frame
The frame should face south. If you are going to have but one frame
you might want to attach it to your south greenhouse wall. If you
plan on a number of frames, build them in rows either free-standing
in the garden or attached to the greenhouse, garage, or other
building.
In cold-winter areas the frames should be provided with a cover of
matting, either the roll-up kind or straw mats. Wooden slats,
cheesecloth, and shading paint compounds help protect plants in the
frame from summer sun.
Here's how we built our cold frame. For the back we used the cement
wall of our garage. The frame is 18 inches high in the back, sloping
to 8 inches in front, to allow water to run off. Lumber, 2 by 12
inches, 14½ feet, forms the front. The sides are 28 inches long.
The lights (three storm sash) are hinged on a 2 by 4 wooden strip
which is nailed to the garage wall.
If you live in a cold climate and plan on using the cold frame for
year-round growing, build it on a concrete or brick foundation which
extends below the frost line. In my area the building code specifies
that the frost line is 42 inches deep.
On sunny days, even in midwinter, you'll have to be careful about
ventilation. Heat can build up rapidly in the confinement of a cold
frame and "cook" the plants. A notched stick will make it easy to
raise the sash cover as needed.
THE HOTBED
A hotbed is basically a cold frame with heat. While cold frames
receive all of their heat directly from the sun, hotbeds are heated
with electric soil cables, stable manure or steam, or hot water
heated with flues. The hotbed can be used earlier in the spring and
later in fall and early winter than the cold frame.
Hotbeds are constructed just the same as cold frames, with a slope
to the south to allow heat from the sun and to allow water or snow
to run off. Plants growing in these frames are protected on cold
spring nights with the same kind of mats suggested for cold frames.
Hotbeds are usually built to be permanent structures, with the frame
of wood, concrete, or brick extending into the ground below the
frost line. As with the cold frame, you can build it yourself,
purchase a kit of materials for building it, buy a ready-built one,
or have someone construct the entire thing for you.
As the spring temperature increases, start ventilating the hotbed by
raising the sash a crack. This applies equally to cold frames. From
midday until mid-afternoon on warm spring days, you will have to
ventilate more. Be sure to close the frame before the temperature
falls at night.
