Cold frames are found in home gardens and in vegetable farming. They create microclimates that provide several degrees of air and soil temperature insulation, and shelter from wind. In cold-winter regions, these characteristics allow plants to be started earlier in the spring, and to survive longer into the fall and winter. They are most often used for growing seedlings that are later transplanted into open ground, and can also be a permanent home to cold-hardy vegetables grown for autumn and winter harvest.
The typical cold frame is (3) foot wide by (4) foot long, but they come in as many shapes and sizes as one's imagination. They can be built as a temporary structure or as a permanent one. The structures can be built from leftover materials to help reduce cost or they can be purchased from many places online.
The concept behind the cold frame structure is to allow the sunshine to come through a transparent top, which provides light and also will heat up the inside area to help plants to grow. The structure can be placed over areas that you want to get a jump start on germinating seeds or early planting. Common produce to plant in cold frames are salad greens and root vegetables.
These structures can be built to where plants or seedlings are moved in and out as the need arises. One of the problems that should be watched out for is overheating of the plants. The roof or top of the cold frame is normally attached to the body of the structure with hinges so the top can be propped open to insert or remove plants, and to let out excess heat.
It takes a watchful eye to be sure you do not cook your young seedlings. It can be surprising how warm the inside can get even during the winter months. One way to take care of this problem is to use an automatic opener that will open the top of the cold frame when it gets warm and will close as the temperature starts to drop.
You may think that this would be something that would require batteries or an electrical source. Actually, it is accomplished by the thermodynamics of wax or other materials that will melt and expand as the temperature increases and will contract as the temperature cools.
The material in the cylinder will expand and contract, thereby pushing one rod which will pull another to open and close the top of the cold frame. Be careful to not let the wind grab the top of the cold frame by attaching a small chain or cord that will prevent damage to the cold frame top and possibly your plants inside.
The first method on cold frame construction comes from Vegetable Gardening For Dummies.
How to Build a Cold Frame for Your Garden
By Charlie Nardozzi and The Editors of the National Gardening Association from Vegetable Gardening For Dummies, 2nd Edition
“A cold frame is, essentially, a mini-greenhouse. By growing plants in a cold frame, you can harvest cold-tolerant vegetables year-round, even if you live in zone 5 where winter temperatures can dip as low as –20 degrees F. Cold frames are also great for hardening off seedlings, growing cold-tolerant flowering annuals like pansies, and rooting cuttings from your garden.
Build a cold frame to extend your growing season.
A cold frame usually consists of a wooden box covered with windowpanes or clear plastic. The frame rests directly over the soil in your yard. You can purchase a premade cold frame for $100 to $200, or you can create your own simple cold frame by following these steps:
This sloping angle enables more sun to reach the plants, and it sheds rain and snow as well.
- Build a 3-foot-x-6-foot box from untreated lumber. Cut the box so that the back is 18 inches high, sloping to a front height of 14 inches.
If the window sash has no glass, use fiberglass or polyethylene to create a sealed growing environment You can insulate the cold frame by adding rigid foam insulation around the insides of the cold frame and by weather stripping along the top edge. In extreme cold, cover it with heavy burlap or an old blanket. Remember to uncover the coldframe when the sun comes out so the plants can warm up again.
- Hinge an old window sash over the top of the cold frame.
If the south side isn't practical, then use the west, east, or north side in that order of preference. It's best to put a cold frame next to a structure, such as a house, to protect it from cold winds.
- Position the cold frame so that it faces south.
Even though the purpose of a cold frame is to trap heat, on sunny days, even in winter, a cold frame can get so hot that it burns the plants. Check your cold frame once a day on sunny days, opening or venting the top slightly to allow hot air to escape. You can even provide some shade by putting a piece of shade cloth over the glass.” (http://www.dummies.com/how-to/content/how-to-build-a-cold-frame-for-your-garden.html)
The second method is from a Mother Earth article on constructing a cold frame.
DIY Cold Frame Plans
By Betsy Matheson Symanietz
Take on this relatively simple DIY cold frame project over the weekend to save money, extend your growing season and become a more self-sufficient gardener.
A cold frame is a simple way to create an area with a stable temperature for giving seedlings a head start in spring and for holding on to the last cold-hardy greens in the fall. You can easily construct your own cold frame, using the pland and instructions found in Weekend DIY Project: How to Build a Cold Frame, and the diagram and charts below.
||3/4 x 16/28 x 36 inches
||3/4 x 16 x 36 inches
||3/4 x 28 x 36 inches
||3/4 x 4 x 31 inches
||3/4 x 4 x 38 inches
||1/8 x 37 x 38 inches
Tools and Materials
(2) 3 x 3 inch butt hinges (ext.)
(2) 4-inch utility handles
(4) Corner L-brackets (3/4 x 2-1/2 inch)
(1) 3/4 inch x 4 x 8 foot plywood (ext.)
1/8 x 37 x 38 inch plexiglass
Exterior wood glue
2 inch deck screws
No. 8 x 3/4 inch wood screws
Straightedge cutting guide
As you can see, there are several ways to build a cold frame, but the construction principles are about the same. This is a good weekend project to get a head start on before the gardening season and to enjoy some early greens.