April 24, 2011

Cold frames extend season

Richard Gast: Cornell Ag Connection

---- — We've all seen how completely unpredictable North Country weather can be. Temperatures often fluctuate wildly and conditions change radically from day to day or week to week, sometimes even from hour to hour.

That lack of predictability can often mean big problems for area gardeners looking for ways to extend what is a very limited gardening season. Wouldn't it be nice to be able to start seedlings or put plants out in late April or early May without having to worry about frost or snow? You can.

Cold frames offer an easy, effective way to protect plants, and extend the gardening season by as much as three months. By using cold frames, North Country gardeners can start planting up to 45 days before they would otherwise be able to, and they can keep plants growing up to 45 days longer at the end of the season. With cold frames, gardeners can grow early (or late) crops of cool weather and salad vegetables, such as lettuce, spinach, radishes and cauliflower, even while there is snow on the ground.

What are cold frames? Simply put, cold frames are just inexpensive miniature greenhouses that can be used for starting and protecting frost-sensitive plants.

The idea is a very simple one. Take the energy from the sun and use it to warm the soil and the air within a contained area in order to create the right conditions for growing happy, healthy plants out of season.

The sun's heat is transmitted through the lid of the cold frame and stored in the soil floor. The cold frame then contains that heat and slows heat loss from the ground during the night. On particularly cold nights, additional insulation, such as old blankets, can be used for added protection. If desired, a supplemental heat source can be placed inside the unit. Almost any size cold frame can be easily heated with a small electric heater.

You can purchase inexpensive, ready-to-assemble cold frames from catalogs or from garden centers, or you can build your own. I've seen all kinds; everything from bales of straw laid out on the ground with an old window placed on top to elaborately designed multi-angular constructions of dimensional lumber, plywood and plexiglas. I've seen a-frames, quonsets, arches. You name it. Plastic is commonly used as a cover, as well.

Cold frames should be built at or slightly below ground level. They should be placed in a garden area where the soil drains readily and where there is no danger of flooding. Some gardeners remove the soil within the cold frame to a depth of about eight to 10 inches and replace it with a thin layer of gravel or course sand (for drainage) topped with soil amended to their needs. A shade-free southern exposure and protection from the wind to the north and west are preferred. Easy access to water and a supplemental heat source are also desirable. Banking soil against the outside of the walls will help with preventing heat loss and keeping the wind out.

On mild days, when there is plenty of direct sun, the air temperature inside of a cold frame can rise rapidly, making ventilation necessary. It is essential that you design your cold frame with this in mind. Use a thermometer to monitor daytime temperatures inside of the cold frame, and ventilate when temperatures approach 70° F.

Careful attention to watering is also a must. Soil should be kept moist, but not wet. It is best to water as early in the day as possible. This will allow plant foliage to dry before nightfall.

Plans for simple cold-frame designs are available through Cornell Cooperative Extension of Franklin County. You can receive yours by contacting Extension at 483-7403.

Richard L. Gast, Extension programs assistant, Horticulture and Natural Resources, Cornell Cooperative Extension of Franklin County, 355 West Main St., Suite 150, Malone, 12953. Call 483-7403 or fax 483-6214.