How to extend the season - maintaining a vegetable garden between fall and spring

Flower & Garden Magazine, Dec-Jan, 1993 by Helen Brassel

If you can't wait to get your vegetable garden started in the spring and hate to see it end in the fall, then simple, inexpensive techniques for extending your growing season are what you need. These techniques work on the basic principle of warming the soil and protecting plants in a restricted environment.

Some hardy vegetables, of course, can make it through a frost on their own in the open garden. Others need help. Spraying the plants with water when cold weather is predicted is a time-honored trick that will protect plants from a frost of a few degrees. Dark-colored plastic bags filled with leaves placed along each side of a vegetable row and covered with plastic or a blanket will retain heat overnight. So will a thick mulch of hay or leaves covered with cardboard boxes, heavy plastic sheeting or old blankets weighted with rocks, but all of these covers must be removed and replaced each day.

Other vegetables need more help making it through cold weather than these temporary methods provide. This help can come in many forms, one of which is the cold frame. A cold frame is nothing more complicated than a bottomless wooden box with a removable transparent cover. The frame should face in a southerly direction-directly south in the fall and winter; southeast in the spring-with the back higher than the front so that the lid slopes. This position exposes the inside of the frame to the optimum amount of sun. The cold frame may either sit on the ground or extend into the ground as much as a foot.

Your cold frame needn't be fancy or expensive. The frame itself can be made from 2-by-2-inch boards topped with a couple of old storm windows. Use whatever is available and build the cold frame to fit. Make the rear about 6 inches higher than the front. Place it on sloping ground and fill it with soil or whatever mixture you prefer if starting seeds. Leave an air space of 12 inches in the back and about 8 inches in the front. The important thing is to leave room for the seedlings to grow without their leaves touching the cold glass.

If you are not handy with a hammer, a temporary frame of hay bales can be made without pounding a single nail. Simply arrange some hay bales into a "U" shape, with the open side of the "U" facing south. Put a glass window on top of the bales and place another at an angle to close off the opening. Once the frame has served its purpose, the hay can be used as mulch.

Don't let the cool spring and fall weather mislead you. Even on sunny days, too much heat can easily build up inside the cold frame. Open your frame a little during the day to prevent over-heating the plants and to allow air circulation.

The simplest way to ventilate one of these frames is to slide the window or cover down an inch or two. Stakes or boards can also be used to prop the lid open at an angle. If daily attending is out of the question, try the automatic temperature-activated vent or lid openers sold at some garden centers.

Keep plants in the cold frames moist, but not soggy. Water in the morning or midday, rather than at the end of the day, when the cool water may reduce the temperature in the frame overnight. If handwatering proves too time-consuming, consider hooking up a mister or soaker hose to keep the plants inside supplied with needed moisture.

Harvesting your vegetables properly is essential to avoid cold damage on days when the air temperature is below freezing. Speed is the key to prevent cold air from invading the protected environment you've established. Pick at the warmest time of day and gather the harvest quickly. If you find ice on some leaves, try not to touch them to avoid damage from breaking.

There are a few other things to keep in mind to successfully extend your vegetable season. Plan your cold frame season with your seed order. Always choose cold-tolerant varieties and check catalogs for estimated time from sowing until seedlings are ready to transplant. And, of course, you can use your cold frame to harden off seedlings before transplanting them to the garden. In the fall, the cold frame can double as a storehouse for root vegetables. Just before the ground becomes too hard to dig, move the root vegetables into the cold frame and cover them with mulch or sand.

Although the versatility of cold frames has made them a popular gardening tool, there are other devices that help extend the growing season. A hotbed is similar in design to a cold frame, but adds an artificial source of heat below the soil of the frame to supplement the heating effects of the sun. Thermostatically controlled, waterproof electric cables do the job today that was once accomplished by thick layers of rotting manure in the bottom of the hotbed. Seedlings and cuttings respond to the bottom heat with faster growth.

A sun pit is a larger, more permanent structure usually built next to the house. It can use a basement window to provide added warmth and ventilation. The walls should be built using earth-filled cinder blocks. The cover can be the same as that used on a cold frame, also sloped and with a southern exposure.