Do you plan to grow your own food this summer? Would you like to extend that growing season a bit more in the spring and fall? If so, there are several options you might consider, including cold frames, hot beds, hoop houses, cloches, and floating row covers.
I remember my dad using a cold frame that he made of old windows to harden off plants in the spring before planting them in the garden. A cold frame is simply a miniature greenhouse that provides warmth from the sun and blocks the wind. The sun's rays enter through a transparent cover and create a greenhouse effect that heats the interior of the cold frame.
Cold frames expand the growing season one to three months. Many gardeners use cold frames to harden off transplants, but another good use is raising a few salad vegetables. Lettuce, radishes, and scallions will grow to full size in a cold frame before their regular outdoor planting season. Or in fall these same crops may be grown in the cold frame through November. Cold frames are also used to store root vegetables over the winter.
There are many different cold frame designs. The most common one is a wooden box with a clear lid that is hinged for easy opening. On a sunny day, the air in cold frames can get too hot for plants. Therefore the lid should be propped open so cold air may enter the structure.
Other designs are much simpler. Be creative. A south or east facing window-well with a plastic or glass covering might work well.
Cold frames can be converted into a hot bed by adding heat. Heat cables and pads are available for this purpose. This gives the added bonus of using the bottom heat to encourage better root growth in plants. Many seedlings require constant warm soil temperatures to germinate, so a hotbed gets them off to a better start.
Another method increasing in popularity is hoop houses. A hoop house is similar to a cold frame, only larger. Metal or plastic pipes are bent into a series of hoops that are stuck into the ground or attached to a raised bed. The hoops are covered with plastic. Hoop houses add six to eight weeks to the spring and fall growing period.
Finally, don't rule out the old-fashioned cloche method. Frequently used for tomatoes or peppers, cloches add three to four weeks to the spring growing season. These transparent "houses" covers a single plant. Examples include empty milk jugs, soda bottles, plastic covered tomato cages, or glass cloches.
This factsheet from Cornell Cooperative Extension gives more information on cold frames.
Build your cold frame today, and you'll be eating fresh greens in a few short weeks. Enjoy!