If I could only pick one season extending structure for a home vegetable garden, it would be a cold frame. Incredibly versatile, a simple cold frame is the key to taking your garden from a two or three-season plot and turning it into a year round vegetable factory. They are easy and inexpensive to build and can be constructed from simple, often recycled materials like scrap wood, straw bales, bricks and old windows.
At its most basic, a cold frame is simply a box with a clear or translucent top. Its purpose is to trap solar energy from the sun and provide protection from the outside elements – cold temperatures, rain, wind and snow. The back of the box is typically taller than the front, which lets the top of the cold frame sit at an angle. This slope allows maximum sunlight to enter the structure and will help it shed excess rain and snow.
In our frames, the first seeding of the year begins in mid to late February when the harshest part of winter has passed and the amount of daylight is steadily increasing. At this time, I seed any empty areas of the frames with hardy crops like green onions, carrots, beets, spinach, arugula, tatsoi, endive and mache. I like to give the soil a boost before sowing, but in mid-winter, the compost pile is frozen solid. Therefore, I rely on vermicompost, which I buy in small bags from a local worm farmer and keep indoors where it won’t freeze.
As the weeks progress into March and spring beckons, more cold and cool tolerant veggies are seeded into the shelter of the frames – hardy lettuces, pak choi and mizuna for example. All of these plantings will provide gourmet salads just in time for Easter!
We continue to harvest through April and May and once the early spring veggies are done, the cold frames are taken out of production for two months. June and July are allocated for soil building, where we incorporate generous amounts of chopped leaves and compost into the earth – I like to add 3 to 4 inches of our homemade compost. It’s also rich in worms, which happily break down the shredded leaves. If the soil pH has dropped, I add powdered lime. If you don’t have compost, sow a cover crop in your cold frames, digging it under a few weeks before you intend to plant.
By late July and early August, it’s time to start thinking about fall and winter crops and I begin the process by transplanting pencil-thick leek seedlings at the back of one of the frames. The winter carrots are also seeded in late July. They’re a true cold season treat and as the temperatures drop in late autumn, the long roots get sweeter and sweeter. In early December, I’ll add a 6-inch layer of straw or shredded leaves to the carrot frames to further insulate the crop.
As August marches on, I make sure that I have enough seed for all the hardy salad crops that we like to grow. If not, a last-minute order goes out to our favorite seed companies. Late August and early September is seeding season for winter lettuces, mache, claytonia, endive, tatsoi, pak choi, spinach, Swiss chard, green onions and more. Even herbs like thyme and parsley do extremely well in a winter cold frame and I move a few plants into the corners of the structures in early September. To get around the hot temperatures of August and September that can inhibit germination, I will start many of my salad crops indoors under my grow lights, moving them into the garden once they’re a few inches tall.
At the end of September, all the crops for fall and winter have been seeded or transplanted into our cold frames and from December until the following May, they’ll provide us with the sights, scents and flavors of spring each time we lift the covers to harvest.
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