In the first part of the post on cold frames I went over variations on assembling your own using the basics. Once you've collected the materials for the cold frame you'll need to decide where to put it. Locations are important for many reasons, most importantly, because it should be sheltered from the wind, but have the best access to the sun.
: Facing the cold frame south is ideal, but if that's not possible, have it face to the east. A location that is sheltered from the western winds is even better. Perhaps it could be placed next to a building, a heavy fence or some other kind of structure that would block the wind. Anything that lends the cold frame shelter without blocking the sun will help it do a better job protecting the plants.
: Most cold frames are not heated, though heating systems are available. There is a method that many gardeners have used with good success that naturally heats the soil in the cold frame. Fresh manure, horse works well, is laid along the entire bottom of the cold frame. The soil is placed on top of the manure. As the manure breaks down it releases heat. If you don't have farm animals, ask around. Usually farmers have more manure than they know what to do with. The soil should be very thick on top of the manure, especially if direct sowing, rather than in a pot.
: The soil used in a cold frame should be rich and fertile, such as what is used in a raised bed. Some gardeners don't add soil, but simply place trays or pots filled with soil inside the frame. Either way, the soil used should be fairly light and fertile. If it's too heavy, peat can be mixed in to lighten it. If it doesn't seem to have enough texture, add compost or other organic material such as leaf mold. To plant directly in the frame the soil should be a depth of 12" to 18".
: The cold frame will heat up on sunny days. If you've ever used a mini greenhouse on the windowsill you'll understand how it works. When the sun is shining directly on the plastic, it heats up and you'll see moisture gathering at the top of the greenhouse. The cold frame will work in a similar way. On those sunny winter days when it really heats up, place a piece of wood, or something that would work in the same way, to prop up the piece of glass on top of the frame several inches. This will allow some air in, and keep it from overheating.
On cold nights the opposite happens and you may need to throw an old blanket, rug or carpet over the top of the cold frame to keep in the heat. Only vent the cold frame for a short period of time during the day while the sun is shining directly on the glass.
How to Use a Cold Frame
Once the cold frame is constructed and the soil is in place, what do you plant? There are a lot of different choices when it comes to planting in the cold frame. In the winter, seeds can be started indoors, and then moved into the cold frame and from there into the garden. When the first seedlings are moved into the cold frame, a new batch of seeds can be sown inside.
Another method is to sow the seeds directly into the soil within the cold frame. The following work well with this method.
Sow these in early fall or late summer directly into the cold frame. The carrots can be covered lightly with straw, as can the radishes. Experiment with different salad greens and you'll find which ones work best in your climate.
In the spring, cold frames can help gardeners get a 4-6 week head start on plants for the garden. Sow seeds of peas, cabbage, greens, spinach, chard, and other early spring crops directly in the cold frame.
Think of the cold frame as a small greenhouse heated by the sun. It will help you extend the gardening season in the fall, and start the garden earlier in the spring.
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