Regional Gardening Reports :: National Gardening Association

In the Garden:
Northern & Central Midwest
February, 2007
Regional Report

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These elegant cold frames are something to strive for!

Start Gardening Early With a Cold Frame

I'm always on the lookout for ways to push both ends of the gardening season, and I've had pretty good luck with cold frames. Even if an occasional plant is lost to frost, succulent greens for salad in very early spring and late fall make a cold frame well worth the extra gardening effort.

Although I have plans to build a permanent frame of wood and glass this summer, for this spring I'll use a discarded bubble skylight cover that I can move around. It has a heavy aluminum frame so it stays where I put it.

Another great option that's easy to construct is a plastic tunnel made of plastic sheeting supported on wire arches. Tunnels, like traditional cold frames, can add six to eight weeks to each end of the growing season. The size of the tunnel usually depends on the materials you use. It can be large enough to walk into or only large enough for the plants to grow, and accessible by rolling up the plastic on one side or end.

Some good framing materials are 5/8-inch electrical conduit bent into arches or, my favorite, flexible PVC pipe. If you don't have raised beds to bolt the frame onto, you can drive heavy wooden stakes or reinforcing rods into the ground leaving about 8 inches showing. PVC arches slip easily over the rods sticking out of the ground. If using wooden stakes, fasten U-bolts onto them and slip the arches into those.

The best plastic to use is greenhouse grade that will last about two years. Standard plastic sheeting usually lasts only one year. When measuring to cut the plastic, make sure you leave enough on the sides to hold down with soil or stones.

Drape the plastic over the arches and then bury it with soil on the windward side and rocks on other side where you need access. The key is to seal out the weather completely, if possible, yet be able to ventilate it on warm days, as well as have access for picking.

Individual Plant Protectors
On a smaller scale than a tunnel, cloches and hot caps allow you to extend the growing season three or four weeks on each end. Traditional cloches, such as the beautiful bell jars of French intensive gardening, are quite expensive, so it usually makes more sense to use the plastic or paper ones that are readily available commercially or to recycle your own milk jugs.

You can purchase simple plastic covers that are meant to be discarded after the season is over, or more elaborate ones, such as plastic sleeves with water-filled tubes that surround the plant with insulation. I use these "Wall-O-Water" mini cold frames to get my tomatoes off to an early start each spring.

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