Vegetable Gardening at Below Zero Fahrenheit - Without Adding Heat
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By Clair Schwan
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Think of this as a December, 2008 progress report for winter vegetables in the southeast corner of Wyoming where we are zones 4 and 5. If anywhere warrants cold weather vegetables, it's right here.
My report begins with a little background. We have a single layer greenhouse with no additional heat. The structure still has its summer vents open at the top, so there is no way of capturing heat from the daytime sun - it simply escapes through the roof into the cold night air.
The crops inside include bok choi, turnips, lettuce and Swiss Chard - all known for their resistance to colder weather, but not the most cold hardy of vegetables. The crops are located in raised beds made of 55 gallon steel drums cut in half so they stand about 1.5 feet above grade level.
The elevated beds absorb heat readily, but they also give off heat more readily to their surroundings. Couple that with the open vents on top of the structure, and you don't have the ideal situation for retaining heat. In addition, there is no other source of heat, other than the sun, and no heat storage mechanism within the 15 by 30 foot greenhouse.
The raised bed steel drums are covered by a 6 mil poly covering. It drapes across the drums and is held off of the plants by PVC hoops that arch across in several places.
Now, for the weather report. Throughout the month of November we generally had low temperatures in the teens and twenties, with a few days dipping into single digits. As usual, after Thanksgiving the weather turned considerably colder as winter settled in.
Early in the month of December, we had temperatures below zero. About 36 hours of continuous below zero temperatures that bottomed out at minus 14F. That's 45 degrees below freezing. Not exactly the type of weather that most would associate with vegetable gardening, but a good test of winter vegetables and their hardiness as bolstered by row covers.
Here are the results of my winter greenhouse gardening experiment. After our spell of bitter cold, I waited a day or so to allow the temperature in the greenhouse to get well above freezing before I checked on our "guinea pig" vegetable crops.
All plants looked like they had taken a little beating, but none were knocked out, froze out, or otherwise destroyed by the bitter cold. They all looked like they were on the road to recovery. It was really an amazing sight.
I harvested the bok choi and found the ground in its raised bed to be frozen solid. The plants were fine, but the ground was solid as a rock. I had to cut it off just above ground level.
A half a dozen turnips were also harvested. A strong pull on the tops freed them from the icy grip of well composted soil. The long tap root came along with the swollen part of the turnip root encrusted with frozen soil.
After a little time to warm up in the house, we prepared our harvest and enjoyed a stir fry of bok choi and fresh slices of turnip that one would expect only in late spring or late fall. Here we were in serious winter weather, and yet we were harvesting vegetables that we planted in the fall.
Just think what could be done with additional row covers, cold frames and more hardy winter vegetables. If you thought that vegetable gardening was just for summer, my experience shows otherwise.
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Author Bio Box: Clair Schwan
 Clair Schwan is an experienced vegetable gardener with greenhouses, cold frames, row covers and open sun garden beds. Read more detail about his winter vegetables at http://www.frugal-living-freedom.com/winter-vegetables.html
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