Most gardeners welcome the change of seasons: the killing frost that allows them to take a well-deserved rest. Others, however, crave fresh salad greens in the middle of winter and are looking for ways to extend the season.
Now is the perfect time to construct a system that will allow you to plant earlier and harvest later — perhaps even into the winter.
There are several ways to do this, but they all make use of three components: cold-hardy vegetables, succession planting, and passive solar principles.
Cold-hardy vegetables include arugula, beet greens, carrots, chard, endive, kale, leeks, lettuce, mizuna, mustard greens, pak choi, parsley, radish, scallions and spinach. These vegetables languish in the heat of summer and perk up once it cools down in the fall. They don’t need long hours of sunshine and can withstand temperatures below freezing.
They do need to be planted at the right time. Succession planting throughout the month of August and early September is best. That allows the crop to mature sufficiently before growth slows down in the short days of November.
In spring, you can begin planting in early March and continue throughout April to harvest before the heat of summer.
The final component of this system is a cold frame — a covering that allows light in and provides shelter from temperature extremes. One gardener I know plants his winter cabbage and parsley in August. When temperatures dip below zero he surrounds the plot with stakes, covers the whole thing with heavy-duty clear plastic, fashions a lid and harvests all winter.
A larger system could involve a frame made of hoops. Use half-inch electrical conduit cut into eight-foot lengths. Insert each end into the ground, forming a hoop over your garden bed. Place hoops three feet apart. Cover with clear plastic, weighed down at each side with bricks, rocks or soil.
On warm, sunny days, you may need to ventilate it by removing some bricks and opening the plastic. In spring, plant early under plastic or simply use a row cover. This has the added advantage of keeping insects from laying their eggs on your crops.
A more sophisticated version can be made of wood with a hinged plexiglass lid. Your cold frame should face south to maximize solar exposure. The interior can be painted white to reflect light and heat, and the lid should slope from back to front. This will maximize the solar capacity of the winter sun, which is low in the sky. The interior temperature can rise to 25 or even 30C on a sunny winter day, so the lid must be designed to open and close as needed.
Check out Lee Valley Tools for a heat-activated opener that adjusts the lid according to the ambient temperature.
Growing Green is prepared by Mount Hamilton Horticultural Society (www.gardenontario.org) and generally appears biweekly. Rita Bailey, the author of this report, is program co-ordinator of the society.