Build a Ventilated Cold Frame For Winter Vegetables

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MOTHER EARTH NEWS STAFF
A partial blueprint of Forbes' creation.

For most of us, the onset of winter means the end of
freshly harvested garden produce — and I used to
hate that! Though I’ve never been able to afford a
greenhouse, I’ve always felt that I somehow had a
right to homegrown salads all year round. Furthermore, I knew that when sun strikes dark soil, it
heats up the earth and the air immediately above it. So, all
I really needed (I decided) was a structure that would let
in the rain and sun, shelter my plants from blasts of
cold air and allow enough ventilation to prevent the
molds, diseases, sour soil and moss so common to
greenhouses. Of course, my invention also had to be
inexpensive, easy-to-build, sturdy enough to stand up
against strong winter winds, and able to coexist with the
four-foot-wide, fertile beds that I’d religiously composted
for five years.

Build a Cold Frame For Vegetables 

Well, my needs and abilities finally got together, and the
result was an 18-inch-high frame — built of 1-by-4s — that fit exactly over one of my raised
vegetable patches. Its sides were enclosed in 10-mil, clear
plastic (polyvinyl chloride), which was secured with tacks
(“washers” made from folded bits of plastic trimmings
prevent the wind from enlarging the tack holes).

Next, I cut 4-inch-wide strips of the same plastic, long enough
to stretch across the width of the top and come down 4
inches on each side. Again using homemade washers, I tacked
the strips in place — spacing them 1 inch
apart — all along the frame’s top. Eureka! My frame was born . . . and it worked!

The sun warmed up the soil and the atmosphere
within the structure by a full 20 degrees Fahrenheit. And, while the
frame protected the plants from the wind, it also provided
excellent ventilation. Rain fell readily through the spaces
between the strips and I could easily slip my hands
through the slots to harvest, transplant and weed.

I hate to brag, but my invention proved to be such a
darned good way to grow things that I decided to use the
frames throughout my garden. For four winters now
I’ve enjoyed lettuce, freshly picked
carrots, beets, parsnips, chard and parsley!

Limit Transpiration For Better Lettuce

Even my brainchild’s one possible disadvantage turned out
to be an asset: I knew the plastic was bound to reduce the
amount of sunshine that reached the plants and less
light (I had thought) would decrease photosynthesis. Well, as it happened, the diminished light was particularly
good for lettuce! It seems that moderate shading
tends to limit transpiration (the loss of moisture)
more than it reduces photosynthesis. Therefore,
the leaves became longer, broader, thinner, tenderer and
smaller-veined . . . precisely the characteristics I
wanted in my lettuce.

But the assets didn’t stop there! I discovered that the
grow-frame also works well in summer, so removing and
storing it for half the year is unnecessary. The
four-season capability of the mini-hothouse was revealed
when, suddenly, it was midsummer and my
plants — still in their winter home — were not only
growing like gangbusters, but needing less water
than did those in open beds.

In fact, the only time I have to water inside the frame is
when I transplant seedlings. As a result, the surface soil
stays dry, while the earth beneath this layer is always
moist. Furthermore, the interior of the frame is never too
humid, so that nasty “brown rot” can’t attack my lettuce.

In addition, when the wind flutters the plastic strips, it
actually sets up afield of static electricity which, some
say, stimulates plant growth. True or
not, I’ve certainly raised some happy-looking vegetables!