Using cold frames is an excellent way to extend a garden growing season past your normal frost and freeze dates.
In their most basic form, cold frames are a four walled structure covered with an angled piece of clear cover. The angled clear top is most often made from glass or plastic.
It works by gathering and trapping heat from sun’s rays during the day. It warms the surrounding air in the cold frame, and heats the soil to keep plants growing. The wall and cover then help to insulate the soil and plants at night as well as temperatures drop.
Cold frames come in many shapes and sizes, and can be constructed of a wide range of materials. Many commercially available cold frames are made from wood and plastic. You can easily create your own as well from hay or straw bales, scrap lumber or even old windows.
All that is really needed is an exterior insulating material and a clear top to allow the sun’s rays to penetrate.
Depending on the style and type used, cold frames can extend a growing season by a few weeks, to throughout the entire winter.
In climates as brutal as Alaska, gardeners use heavy-duty cold frames to grow fresh vegetables all winter long! In addition, they can be used to sprout and raise transplants in the early spring.
Top Keys To Using Cold Frames
Cold frames need to have their angled clear tops facing to the south. This allows for the maximum amount of the sun’s rays to be captured as the sun arcs across the winter sky.
For best results, the frame should be tilted at least 10 degrees toward the south.
Frames can be laid perfectly flat, but with the shorter sun arc during the fall, winter and early spring, the cold frames have less time to capture the rays. By tilting, it allows the cold frames to soak in the early morning to help reheat the soil and air lost from overnight cooling.
Well drained, fertile soil is a must when growing in cold frames. Fill your frames with either a good potting soil, or large amounts of compost. See : How To Make Great Compost
Plants growing in the cooler months need all the help they can get sprouting and growing. Product Link : Organic Potting Soil
Controlling The Temps
Keeping the temperatures moderated inside of the cold frame is a big key to success. As much as a cold frame protects plants against freeze and frost, they can overheat seedlings and plants quickly if the air and soil get to warm.
On warm days, windows need to be propped open to keep plants from “baking” inside of the cold frame.
One of the easiest ways to control this is with an automatic vent opener. These little gadgets have become popular with cold frame growers over the years as a way to easily help regulate temperatures.
They use the same technology that automatically open windows used in greenhouses when the air temperature becomes too hot. The solar versions operate without the need for power, install easily to window frames, and can lift windows up to 15 pounds.
Most vent openers are adjustable, and will open or close the window when the temperature reaches above or below the 55 – 75°F range. Product Link : Univent Automatic Vent Opener
Using Cold Frames – What To Grow
Although it is quite possible to grow nearly anything in a cold frame, fast growing and hardy greens are among the best for winter-time or late season growing.
Kale, spinach, radishes and nearly all types of lettuce are well-suited when using cold frames.
Cold frames can also be a great asset in the spring. They are a wonderful way to raise tomato, pepper, cucumber and other transplant vegetables. The seeds can be started in the frames, and transplants can have protection from early spring frosts.
Although you can easily construct your own from simple materials, here are a few commercially available cold frames that work great too.
3.5mm polycarbonate for maximum insulation and heat retention over winter
Can be used directly on the ground. Has fully opening for easy access. Clear top is made from shatter proof material.
Twin-box raised bed planter is made from heat insulating and frost resistant hollow bricks.
Each section (24″) comes with a removable cold frame cover (5″ high) made from twin-wall polycarbonate
Whatever you choose to use, using cold frames are a great way to keep gardening all year long!
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