Lengthen Growing Season By Building Simple Coldframe or Cloche

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Last Updated: 
May 30, 2008

CORVALLIS, Ore. - Do surprise frosts or cool temperatures foil your plans to ripen peppers or tomatoes? Do you want to keep lettuce or other greens growing over the winter? Oregon State University Extension Master Gardeners are encouraging beginning home gardeners to try building a simple cloche or coldframe this fall to lengthen your growing season.

Coldframes can prolong the growing season in the fall and be used to start flower and vegetable plants before normal outdoor planting dates in the spring. Young plants are protected from frosts, from pummeling rains, from the damage of icy sleet or winds. The sun enters the clear top of the coldframe by day, heating the soil. At night, the coldframe slows the loss of heat.

Built with wood or metal sides, coldframes can have a hinged or removable clear top of glass, plastic or fiberglass, so the cover can be raised on warm sunny days and then lowered during cool nights. Side walls can be as high as needed, but eight to 12 inches are the usual height. The north wall of the frame box is usually built higher than the south for better sunlight exposure. A clear top with two layers or fiberglass works well. Plain clear glass or clear plastic does not hold in heat well overnight.

For an easy inexpensive cloche, retired OSU Master Gardener program assistant Pat Patterson recommends building a cloche out of concrete reinforcing wire.

"I have used these wire mesh frames for cloches for years and they nest well for storage," said Patterson.

Patterson suggests buying a roll of mesh and cutting it to form "Quonset hut" hoops as high and as wide as needed to cover an area you want to protect. Concrete reinforcing wire comes in five- and seven-foot rolls, so plan accordingly.

Place a section of the mesh over the plants to be protected and cover the reinforcing wire with 2 layers of clear plastic or one layer of row cover plus one layer of plastic. "Even old bed sheets will work if you just need night time protection from frost," she added.

To learn more about building coldframes and hotbeds, the OSU Extension Service offers a fact sheet, FS 246, "Constructing Coldframes and Hotbeds" on the Web at: http://extension.oregonstate.edu/catalog/html/fs/fs246-e/

Author: Carol Savonen
Source: Pat Patterson