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Tools to Extend the Growing Season

By Patti O'Neal, master gardener, Denver County office of Colorado State University Cooperative Extension

"Mary, Mary, quite contrary - How does your garden grow?"

With row covers, grow tunnels, Walls O'Water, cold frames and hot caps all in a row!

By taking advantage of several techniques, Colorado gardeners can enjoy their garden bounty long before the last spring frost and long after the first fall frost. These gardening accessories will moderate the temperature around your plants in the weeks before and after frost dates.

  • Cold Frames have been termed the poor man's greenhouse because they're simple to make from scrap lumber or hay bales covered with old window sashes. They're called "cold" because they have no internal heat source. Warmed by the sun, they're really a bottomless box with a southward sloping, translucent lid. These simple shelters allow you to grow cool season vegetables and flowers early in the season as well as into the winter. Some gardeners add an automatic vent to open and close the lid; by venting you avoid "cooking" the plants on sunny days, and you can trap heat inside at night.
  • Various weights of garden fabrics are available. Made of polyester or polypropylene, the heaviest row covers provide protection to 28 degrees while allowing sunlight, water and air to pass through to promote growth. Easily cut to fit any garden area, these devices often are termed "floating" row covers because they float on plants as they grow. They can protect young plants in the spring and extend the life of mature plants in the fall. Floating row covers also can be used to protect crops from insects.
  • Grow tunnels work for either rows of plants or a single plant as large as a young tree. They are made of plastic or fabric stretched over chicken wire or wire hoops, and their edges can be secured to the ground by pins or soil. Unlike floating row covers, an enclosed grow tunnel prevents winds from circulating under the edges of the cover and stealing heat. Plastic row covers usually are used for a short time because of the necessity of raising and lowering the sides to ventilate the tunnel on hot days.
  • Walls O' Water is a trade name for a cone-shaped plant cover that fits around individual plants. The flexible, double-walled plastic is filled with water for support. This design also takes advantage of the heat generated from the water to create a growing environment within the cone. The top can be spread open for ventilation or, during cold periods, gathered closed for greater heat retention. Walls O' Water provide excellent wind protection and are particularly good in the spring for starting vegetables such as tomatoes and peppers.
  • Hot caps are cones of paper that you can purchase or make from newspaper or other materials. Many fast food containers and milk cartons can be recycled to provide short-term frost protection for small, tender transplants early in the spring.
  • Greenhouse umbrellas are large individual plant covers that resemble a high-crowned umbrella with transparent plastic sides. The sharp center stake is anchored in the ground over the plant and the sides drape around it. Avoid use where high winds are a problem.

Photo: Judy Sedbrook

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CSU/Denver County  Extension Master Gardener 2010
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Date last revised: 01/05/2010