Cold frames help backyard gardeners to give plants an early start while protecting them from frost, cold temperatures, and even nibbling animals. Learn how to build a cold frame in your garden today.
What Is a Cold Frame?
When I was a kid, I remember my great-grandmother covering long columns of the garden bed with white cloth, supported by hoops. It was as if huge pale caterpillars had taken over the garden. What is this cold frame, though, and how does it work?
If you’re a plant parent, you’ve likely had the experience of covering a tender plant with a blanket or a bedsheet to protect it from an unexpected frost. Cold frames accomplish the same purpose but eliminate the “unexpected” aspect.
Just like a greenhouse (or the Earth’s atmosphere), cold frames are constructed of materials – translucent plastic or fabric – that allow an amount of sunlight to pass through. Some of that energy is captured, warming the air inside. The material also prevents damaging frost from reaching the leaves.
When Should I Use a Cold Frame?
Here in USDA planting Zone 7, I like to set up cold frames in February to get a head start on spring crops like lettuce and peas. I leave the frames in place until all danger of frost is past. Likewise, erecting cold frames over your garden as the first frost date nears can extend your growing season by weeks or even months.
Additionally, cold frames can be used to provide shade to sensitive plants such as rhubarb or tea. They can also be helpful in hardening off seedlings started indoors. The cloth may prevent the leaves from becoming sunburned as they transition to life outdoors.
Where Can I Get a Cold Frame?
Amazon, Walmart, and most farm supply and home improvement stores sell cold frame kits, or you can flex your DIY muscles and build your own using a few common items, some of which you may already have.
How to Build a Cold Frame
Building your own cold frame is easy. You can set up your cold frame in minutes by following these three steps.
Step 1: Secure the Framework
You can purchase cold frame hoops, or you can build your own. I recommend using field fencing with large openings. First, determine how long you need to cut the fencing to make a half-circle shape over each row or raised bed. For my 3-foot-wide raised beds, I cut 4 to 4.5 foot lengths of fencing.
If you’re working with wooden-sided raised beds, securing the framework is easy. Simply stretch the fencing so that the ends meet the ground on the outside edges of the bed. The pressure that the wire exerts as it tries to re-roll itself will hold the frame in place. You can drive the wires into the dirt for an even firmer hold.
If you are covering rows in an open garden area, you may wish to use large metal staples or tent stakes to keep the cold frame in place. Simply place the stake over the fencing wire and drive it into the ground.
Because the metal wire fencing comes it a roll, it naturally assumes a round, half-circle shape.
Step 2: Measure and Cut the Fabric or Plastic
Unroll the fabric or plastic you plan to use for your cold frame. Place the fabric over the frame. Allow enough overhang to cover the open ends of the frame, and cut to size.
Step 3: Secure the Fabric
Cold frame fabric is lightweight and can easily be caught be the wind. You’ll need to secure the fabric on all sides.
My favorite and perhaps the easiest method is to weigh the fabric down. On each side, allow a few inches of fabric to lay flat on the ground. Then place your weights. You can use anything you have on hand – bricks, blocks of wood, lengths of pipe, flower pots, or rocks.
Alternatively, you can use staples, tent pins, thumbtacks, or small nails to secure the fabric to the wooden garden bed or directly to the ground. Remember, however, that you don’t want to make these attachments too permanent – you’ll want to open at least one side to check on and water your plants, and you’ll likely remove the frames entirely when warm weather arrives.
Once you set up your cold frames, you’re ready for a long gardening season. When you take down your cold frames, retain the fencing and fabric for future use.
Tip: If temperatures dip below freezing, the cold frame alone won’t be enough to protect some plants. You can sometimes remedy this by placing a string of incandescent bulbs inside the cold frame. Unlike LEDs, incandescent lightbulbs produce a small amount of heat – in some cases, enough to save your plants from a snowstorm.
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Cara Siera is a freelance writer and photographer with a passion for travel and exotic cuisine. Join Cara, her husband Marc, and one very spoiled German Shepherd on their next great adventure.