For gardeners who like to start their own vegetable or annual flowering plants in the spring, either a hotbed or a cold frame can be a useful investment. Plants can be started outdoors in the spring and grown to transplanting size by the time the garden is ready. The cold frame is simply an unheated translucent structure that gives protection to the plants from wind, rain, and, to a limited extent, cool temperatures. It is not heated, but an insulated cover can be used on cold nights to retain heat. Solar radiation from the sun warms the air and soil during the day. The hotbed has a source of heat built into the structure. In earlier models, decomposing manure provided the heat; now, however, electric heating cables and other fuel sources are used. The hotbed extends the useful growing season: plants can be started while outside temperatures are still below freezing. Either of these structures can replace the home greenhouse for many outdoor gardeners. This publication describes how to build these structures.
Location
Hotbeds and cold frames should be located in a protected place with a southern exposure to
receive the maximum amount of sunlight. (A lack of good sunlight can result in leggy plants, stretching in search of light.) They should be close to a source of water and to electricity if they are electrically heated or lighted. A building or other windbreak on the north or windward side will help to reduce the operating cost. The site should have good, natural drainage to remove excess moisture from the soil under the structure. thermostat. Guidelines for sizing these are covered under the section on heating.
Site Preparation and Construction
It is important to prepare the site properly to ensure a level bed, weather protection and good drainage. For good drainage, a base of gravel is recommended and, if conditions warrant, drain tile should be installed to remove surface or ground water.
Manure-heated hotbed. To build a manure-heated hotbed, excavate the bed area to a depth of 14 inches and fill with 10 inches of well-packed green manure. On top of that put 4 inches of loam soil. The wall of the frame will sit on the ground around the filled pit (Figure 10).
Electrically-heated hotbed. To build an electrically-heated hotbed (Figure 11), excavate the bed area to a depth of 14 inches and fill with 6 inches of gravel, well-tamped down. Cover the gravel with burlap or plastic screening that will support soil or sand and prevent it from moving down into the gravel. Add 2 inches of sand, the heating cable, and another 2 inches of sand. (The sand provides a protective layer for the heating cable.) Moisture in this layer during the heating season will move the heat to the soil and plants above. Over the sand, place a ½-inch protective layer of mesh hardware cloth. Finally, add 4 inches of soil or other growing medium. Prepared mixes can be purchased, or use a 1:1:1 mixture of rotten leaves, garden soil, and sand. Have the growing medium tested for fertilizer and lime requirements. The Cooperative Extension Service will conduct the test for a small fee.
Credit :
Hotbeds and Cold Frames for Starting Annual Plants
by
David S. Ross
Extension agricultural engineer
Department of Agricultural Engineering
Location
Hotbeds and cold frames should be located in a protected place with a southern exposure to
receive the maximum amount of sunlight. (A lack of good sunlight can result in leggy plants, stretching in search of light.) They should be close to a source of water and to electricity if they are electrically heated or lighted. A building or other windbreak on the north or windward side will help to reduce the operating cost. The site should have good, natural drainage to remove excess moisture from the soil under the structure. thermostat. Guidelines for sizing these are covered under the section on heating.
Site Preparation and Construction
It is important to prepare the site properly to ensure a level bed, weather protection and good drainage. For good drainage, a base of gravel is recommended and, if conditions warrant, drain tile should be installed to remove surface or ground water.
Manure-heated hotbed. To build a manure-heated hotbed, excavate the bed area to a depth of 14 inches and fill with 10 inches of well-packed green manure. On top of that put 4 inches of loam soil. The wall of the frame will sit on the ground around the filled pit (Figure 10).
Electrically-heated hotbed. To build an electrically-heated hotbed (Figure 11), excavate the bed area to a depth of 14 inches and fill with 6 inches of gravel, well-tamped down. Cover the gravel with burlap or plastic screening that will support soil or sand and prevent it from moving down into the gravel. Add 2 inches of sand, the heating cable, and another 2 inches of sand. (The sand provides a protective layer for the heating cable.) Moisture in this layer during the heating season will move the heat to the soil and plants above. Over the sand, place a ½-inch protective layer of mesh hardware cloth. Finally, add 4 inches of soil or other growing medium. Prepared mixes can be purchased, or use a 1:1:1 mixture of rotten leaves, garden soil, and sand. Have the growing medium tested for fertilizer and lime requirements. The Cooperative Extension Service will conduct the test for a small fee.
Credit :
Hotbeds and Cold Frames for Starting Annual Plants
by
David S. Ross
Extension agricultural engineer
Department of Agricultural Engineering
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