Cold Frames & Hotbeds

Getting plants off to an early start enhances both maturity and production. Hotbeds and cold frames provide an inexpensive way to start plants before the normal growing season and are substitutes for a greenhouse. They are much small and less expensive to build and operate. They are excellent for starting plants earlier in the season or for hardening off plants for setting them out in the garden. Face hot beds or cold frames toward the south, the best exposure to the light and warmth of the sun. A windbreak on the north side makes the bed easier to heat. Choose a site that is well drained and not subject to dripping from the building. Mulching around the frame will help to insulate it from the cold. Hot beds and cold frames are not the same because they are heated differently. Hot beds are usually heated with electricity or decomposing organic matter such as barn yard manure. Buried electrical cables are a common way of heating hot beds although some use an incandescent light bulb. Hot beds are used to start plants ahead of normal planting time to allow for an earlier harvest. Cold frames can also be used to start plants although it is often not early enough to make a substantial difference in the harvest. Cold frames are used to protect and harden off young, tender plants that are started in the hot beds. Cold frames can also be used to grow out of season crops including some flowers, salad crops, and cool season cole crops. Most gardeners could use both the hot bed and cold frame and start their plants. The hot bed is used for germination and early growing and the plants are transferred to the cold frame as they continue to grow. Cold frames should be larger than the hot beds as the plants grow, expand and take more space. Both hot beds and cold frames should be covered with some transparent blazing materials. If you use glass, it should be tempered to avoid the danger of someone cutting themselves should the untempered glass break. Clear polyethylene or rigid plastic can also be used as a glazing material. In addition to heating, make provisions for cooling the structures. Overheating actually causes more failures than frost. Lifting the lid is an easy way to provide adequate air circulation but this system requires that you take care of the task on an as needed basis. With unpredictable spring weather you may need to open and close the lid manually several times each day. A small, thermostatically controlled, electric fan will ventilate most cold frames. If you want to avoid electrical controls, a solar operated vent is available. A small cold frame holds several flats of plants. This will supply most gardeners with both flowers and vegetable transplants. Pest problems are usually minimal if sterilized soil and clean containers are used. Since the plants are at ground level watch for snails and slugs. They can devastate new seedlings and destroy several flats of plants in one night. Use baits or handpick and destroy the pests as needed. Larry A. Sagers Regional Horticulturist Utah State University Extension Service Thanksgiving Point Office