Cold frames are an excellent way to extend the winter garden.  Cold frames are a miniature portable greenhouse. Using one means winter doesn't have to put a stop to food gardening. A cold frame can be set up over a section of your vegetable garden as winter approaches. In winter, a cold frame can help your overwintering vegetables thrive, and help you get an earlier start on planting other crops.

Cold-frame basics:

  1. how to build it
  2. how to site or place the cold frame
  3. what and when to grow.

Build it: To get started, clear a flat garden space the size of your future cold frame, then lay a brick or stone base on which to set the cold frame.  A cold frame can be made from new or recycled materials.  One of my favorite designs can be found on  If you want a more traditional cold frame then you will need the following items: An angled pane of glass or plastic that will sit upon a sturdy base for the top. An old window or door makes an excellent top.  The top will be removable or easy to tilt up (attached with hinges to base) for access to plants. You must also be able to prop it open for venting. Build the wood frame (four sides and a top, with an open bottom) using boards that are sturdy enough to support the top but light enough to move easily. The front and back will be rectangles with the back taller than the front, and the sides will have an angled board. The top will angle down toward the front wall. The back wall should be at least six inches higher than the front wall to create at least a 10-degree angle, which will shed rain and gain more light. The angle can be up to 45 degrees.  The sides can be solid wood boards or can be made as frames that plastic or glass can be attached to in order to let in more light.  Plastic and glass sides will let in more light, but will require more attention and venting on sunny days to keep from stressing the plants. Build each wall separately, then connect them with screws or bolts for easy dismantling and storage. If using a light plastic top, fasten a sturdy cord or small chain between the top and a side wall so it won't swing open in windy conditions. Use a garden stake to prop it open when working or venting.Further refinements include painting the wood for weather-resistance. Use a light color to reflect more light back onto the plants. If the top is made of lightweight wood and plastic, use bricks to hold it down in the wind, or add eye hooks between the top and side walls. Add a handle to the top.

The right siteYour first consideration is where to put it. Ideally, it should be in the warmest spot in your garden, the place where hot summer crops do best. For most light, it should get south and west exposure.Site it away from trees or shrubs for the best access to low winter sun. A spot protected from the wind will help, too.Finally, place it next to a stone walkway to make for relatively dry and clean access during wet weather. If you need to get muddy to work in it, you may find yourself visiting it less often, and regular monitoring of the plants is necessary.Use it for seedlingsIn January and February, the cold frame can be used to grow seedlings started indoors. As the soil warms and days lengthen, seeds or seedlings can be planted in the soil inside the cold frame.If starting seeds indoors, "harden off" the seedlings by setting them out for a few days during the day before transferring them full time to the cold frame.Seeds such as lettuce, endive, leeks and onions can be started indoors in January to transplant outdoors. By February, very hardy vegetables and herbs can be sown outdoors in a cold frame. Get an early start on peas or fava beans, radishes, arugula, beets, spinach.On nice days, monitor conditions in the cold frame. It can get too warm for delicate seedlings, and must be vented. It can also dry out much more quickly than you'd imagine, especially if you are growing plants in small pots. Soil should remain moist but not soggy.As seeds grow, watch for slugs and snails. They seek out tender young leaves, and love to hide under shady edges of wood or stone frames.Check regularly for plant diseases. Seedlings should be given generous spacing to avoid cultivating the soil-borne fungi that cause damping off disease (which is the seed rotting before germinating, or the seedling stems rotting at soil level).