|The Cactus Patch|
|THE NEWSLETTER OF THE BAKERSFIELD CACTUS & SUCCULENT SOCIETY|
|Volume 10 February 2007 Number 2|
|Frost Protection and
Extending the Growing Season
by D. Whiting, C. Wilson, and C. O'Meara
Colorado State University Cooperative Extension
Blankets and Sheets
Floating Row Covers
Plastic Covering on Frame
Plastic Covered Cold Frame Made with Concrete Reinforcing Mesh
An easy cold-frame structure for a growing bed is made with 4-mil clear plastic (polyethylene film) draped over concrete reinforcing mesh. The structure is easily opened during warm days and closed for cold nights. It works well with a 4-foot wide, raised-bed garden system.
The frame is concrete reinforcing mesh, available at hardware and lumber stores. This stiff wire mesh typically comes 5 feet wide in 50 and 100-foot rolls. A 6-foot length is required to make a Quonset-type frame over a 4-foot wide growing bed. In trials, the low and spreading shape was ideal for trapping heat from the soil during a frosty night. Cover the frame with clear, 4-mil polyethylene plastic. It typically is sold in 10 foot by 25 foot rolls. For a 4-foot wide raised bed box, place a 31/2-foot wide section on each side, overlapping at the top. On a raised-bed box, staple the plastic to the sides of the wood box. In soil bed applications, bury the plastic a few inches along the sides.
During the day, the covering MUST be opened, at least a slit, to prevent overheating. With just an hour of sun, temperatures under a closed cover can quickly rise to over 130F! Cover must be opened at least a slit to prevent overheating. On cool days, open the top a crack to prevent excessive heat build-up. On a warm day, the plastic can slide down the side, ventilating and providing crops exposure to the outdoors. On freezing nights, close the cover completely. On warm nights, leave the covers open a crack. On stormy days with full cloud cover and no direct sun, the cover may remain closed. Not only will the covers provide frost protection, they also increase growing temperatures for early crop growth and provide protection from cold winds.
In trials in Fort Collins, Colorado, a plastic cover on a frame typically provides 3 degrees F to over 6 degrees F of frost protection. It works well for cool-season crops that are somewhat tolerant of frosty nights, and adds two to six weeks or more on both ends of the growing season. For warm-season tomato and summer squash crops that are intolerant of a frosty nip, adding a small light inside the cold frame provides even better frost protection.
Adding Space Blankets
On extra cold nights, placing an aluminum space blanket over the plastic on the frame significantly adds to the frost protection. With the aluminized side placed down (towards the plants), a space blanket reflects 99 percent of the heat. They are readily available where camping gear is sold. In trials in Fort Collins, topping a plastic-covered, concrete mesh cold frame with a space blanket prevented freezing when outside temperatures dipped to 0 degrees F following a sunny spring day. Remove the space blanket each day to recharge the soil's stored heat.
Lights for Additional Heat
Christmas tree lights – For additional protection, add Christmas tree lights inside the cold frame. In Fort Collins trials, one 25-light string of C-7 (mid-size) Christmas lights per frame unit (4 feet wide by 5 feet long) gave 6 degrees F to over 18 degrees F frost protection. Lights were hung on the frame under the plastic and turned on at dusk and off at dawn. Christmas lights work better than a single, large light bulb in the center by eliminating cold corners and edges.
Space Blanket with Christmas Tree Lights
For the gardener really wanting to extend the growing season, try Christmas lights plus a space blanket. One 25-light string of C-7 (mid-size) Christmas lights per frame unit (4 feet wide by 5 feet long) with a space blanket on top gave 18 degrees to over 30 degrees frost protection in Fort Collins trials.
The wall-of-water is a cone-shaped ring of connected plastic tubes filled with water that surrounds a single plant, like a tomato, pepper or summer squash. This device works on the chemistry principle of heat release in a phase change; there is a significant amount of heat released as water freezes (changes from the liquid phase to the solid or ice phase). A wall-of-water provides frost protection typically down to mid-teen F temperatures. It also provides wind protection for tender plants and growing temperatures may be slightly warmer inside a wall-of-water. They are helpful to get a few extra weeks head start on vine ripe tomatoes. However, an extra early tomato may out-grow the protection and the tops may be nipped back by frost. Both cold air temperatures and cold soil temperatures are limiting factors in early crop production. When using a wall-of-water to start early crops, warm the soil with black plastic mulch.
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