COVERSTORY
Cold Frames
A
cold frame greenhouse may be one of the
most valuable tools used by a horticultur-
ist. The term “cold frame” refers to the fact
that the greenhouse is not heated. Histori-
cally, cold frame greenhouses were built to be used
in conjunction with a heated greenhouse. In many
cases, they were built adjacent to the heated green-
house. This allowed the seeds to be germinated in the
heated greenhouse and then moved to the cold frame
greenhouse to be “hardened-off” before being planted
outdoors.
There are many different styles and sizes of cold
frame greenhouses, but each serves a similar purpose:
to create a microclimate that shelters plants from the
wind and extreme cold. In geographical locations with
cold winters, a cold frame enables a horticulturist to
start his or her plants earlier in the spring and then
keep them longer in the fall. Simply put, using a cold
frame greenhouse can help a gardener extend his or
her growing season. Some growers, depending on
their geographical locations, use cold frames through-
out the winter to either protect dormant plants until
spring or to continue harvesting root vegetables and
cold tolerant greens.
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Another advantage of a cold frame greenhouse is
being able to grow, harvest and bring particular crops
to market earlier than normal. The soil and plants
contained within a cold frame greenhouse will be kept
approximately 5-10 degrees warmer than the ambient
outdoor temperature. This usually allows a gardener
to start the acclimation process a couple of weeks
before the area’s average last frost date. Because cold
frames allow a horticulturist to start their crops earlier,
it is possible to harvest the vegetable crops ahead of
the normal season. During this time, the normally out-
of-season vegetables are more expensive and a grower
is able to capitalize on the higher prices.
Acclimating (Hardening Off)
In order to properly acclimate young plants to
outdoor conditions, the plants must be slowly exposed
to their future environment. A cold frame greenhouse
works great for keeping young plants sheltered, while
giving them a “taste” of outdoor life. The acclima-
tion process, commonly referred to as hardening off,
reduces the chance of transplant shock and thickens
the cuticle (the waxy protective covering on the leaf’s
surface) which reduces the amount of water the plant
will transpire.
www.GardenandGreenhouse.net
April 2018