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Cold Frames

With all the emphasis on growing fresh vegetables, I think I should use a cold frame but I am not sure what to do or how to go about it. Any ideas?

Cold frames are simply four walls with a window or plastic sheet on top. They range from simply placing four bales of straw in a square with an old window atop them to more deluxe mini-greenhouses with aluminum frames, plastic panels and automatic vents using solar energy to open and close them automatically.

Before building a cold frame, study garden supply and greenhouse catalogs to determine your needs and how fancy you want your cold frame to be. Do you prefer a permanent installation or an easily disassembled frame?

A basic plan for building a cold frame is taught by Chicago Botanic Garden’s senior horticulturist Heather Sherwood. Create four walls from plywood or bricks. Add a transparent lid (plastic sheeting or an old window) for light to enter. Place the lid on an angle. Place the frame against a building, facing south. Make sure there is good drainage. Open the frame when it gets above 60 degrees. Rabbits don’t usually get into the box but chipmunks may squeeze in.

Cold frames are used for extending the growing season, starting plants early, for storing bonsai or protecting semi-hardy plants over winter. The soil in the frame depends on how you will use it. The frame can be set on existing soil when you are storing plants, or fill it with straw to protect bonsai. Locate it conveniently against the house near a back door for easy access, especially if you envision running out to cut some salad greens when snow is on the ground.

Use a cold frame to get a head start on the gardening season. In early spring, start flats of lettuce, radishes, parsley, pansies and other cool-weather plants in the house, and place them in the cold frame in March, depending on the weather. If you plan on planting directly into the cold frame, fill it with a seed starting soil mix and an inch of compost worked into the top 3 inches of the soil. This will help keep the soil loose and aid moisture retention. The plants will be small in the cold frame and can be grown close together. Also use the cold frame to harden off house-grown seedlings.
Don’t forget to check on your plants regularly because winter sun is strong and plants dry up easily. Use it for a head start on the gardening season.


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