Even though Winter is with us for a few more weeks, you can still start the seeds that will grow into the herbs, flowers and vegetables of your spring and summer gardens. The secret lies in the humble cold frame, an easy-to-construct and simple-to-use innovation that makes early- and late-season gardening not only possible, but fruitful as well. All it takes is a little know-how, and some spare building materials!
What is a cold frame?
A cold frame is, at its essence, a sheltered growing space, much like a miniature greenhouse. While the size and appearance of cold frames vary widely, most are simply boxes, covered with a transparent glass or plastic lid that can be opened and closed. Cold frames are called as such to distinguish them from other sheltered-growing areas that are heated, such as greenhouses.
What is it used for?
Cold frames are generally used as “season extenders”—that is, they provide a place to grow vegetables well before—or well after—their traditional growing season. By using a cold frame, gardeners can grow fall vegetables well into the winter, since the cold frame provides insulation that serves as a barrier to extreme cold, snow, rain or wind. Alternatively, cold frames can also be used in the very early spring, as a place to raise and harden-off seedlings that will later be transplanted out into the garden.
Where should my cold frame be placed?
In the Northern hemisphere, cold frames are typically placed on the south side of the property, usually against a building, in a place where they will receive ample sun even throughout the autumn and winter. Cold frames are typically built squat to the ground, where they can maximize the insulation qualities of the soil. (Consider the wind and draft that a cold frame would be subject to if it were raised up upon legs; with airflow all around the cold frame, the temperature inside the box would not be able to stay elevated.)
How is a cold frame made?
Cold frame construction is quite easy, since it is basically just a box. Typically the box has a slight slant from a higher back to a lower front, in order to capture the most sunlight throughout the day, and provide good drainage for the runoff of rain. The lid is usually hinged, for convenience, and is constructed using an old window or piece of plastic for the transparent medium. There are no exact or preferred measurements for a cold frame; the most important thing is that the frame is situated wisely, and that it is relatively well-sealed. There are plenty of guidelines and plans available online, but anyone with very basic carpentry skills can probably intuit the process for making a cold frame from looking at photos.
How do I use the cold frame?
Once the cold frame is constructed, it should be filled with a high-quality growing soil that has been amended for the vegetables or herbs that will be planted. Plant the seeds in a rowed or broadcast style, and let the cold frame do its magic. Even through the cold and inclement weather of the fall, winter and early spring, the seeds will sprout in their moist, warm home, and amaze you with the rapidity of their growth.
Remember to check the soil in the cold frame for moisture, and, most importantly, always open the cold frame on any particularly warm days; the transparent lid of the cold frame, so important when it is cold outside, can act like a magnifying glass on the warmest of days, burning your seedlings and veggies.
You can let plants cycle into full maturity within the cold frame (to grow vegetables during the winter, for instance), or transplant seedlings out into the garden once they have been hardened off within the cold frame. Once the cold frame has been cleared, simply check the condition of the soil and then start again!
Also Checkout:
How to Build a Square Foot Garden
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Can these be used in conjunction with timber raised garden beds?