How to Build Cold Frames

How to Build Cold Frames

Earlier in the year I wrote a post on winter gardening and briefly mentioned the cold frames that you are going to need to grow one.  This post contains more complete instructions for how to build them.

Cold frames are the means in which to grow a winter garden.  There are some pricey options you can buy online, or you can make a better one very simply (and cheaply!) by yourself.  All you need is:

  • Four two-by-fours
  • A sheet of twin wall polycarbonate (or other greenhouse material, but the twin wall polycarbonate is a better material)
  • Some nails.

So how does a cold frame work? During the day, the sun passes through the greenhouse material, and the frame traps the heat during the day keeping the plants from freezing.  As the sun sets the air in the cold frame gradually cools, and the warmth from the ground keeps the temperature in the frame above freezing.  This process will take place even when the cold frame is covered in deep snow, and in fact the snow will act as an insulator for the cold frame.

A good cold frame is as low to the ground as you can manage it, as it will retain heat from the ground much better during the nights and avoid freezing.  For most plants, this will be around 6-8 inches tall.  For taller plants adjust as needed, but keep as low as possible.

Instructions for Cold Frames:

1.  Gather four 2×4’s and nail together in a rectangle.  Keep your rectangle accurate to the dimensions of your twin wall polycarbonate/greenhouse material so it will cover.

2.  Nail down your twin wall polycarbonate/greenhouse material on all four sides to the 2×4 frames you have built.  *Note: I usually make more 2×4 frames than I have greenhouse material for.  This way I can stack the frames double for some of the taller plants.



3.  When temperatures start dropping near freezing, cover your plants!

I told you it was simple!  Don’t worry if the frames have very small cracks that air can flow through; as long as there are no gaping holes, you are good to go.

There are a few other things you can make a cold frame out of.  Do you have an old window, or an old glass door? Lay that on a frame of wood, mounds of raised soil, or even bales of straw (which are excellent insulators).  Careful not to shatter the glass though, as it never really decomposes and can make areas dangerous for walking.

There are just a few things to remember: avoid opening your cold frames except on warmer winter days to protect the plants.  Also if the days become too warm and sunny (approximately above 60 degrees), watch out because you may just bake your plants!  And finally, remember that even during the winter you will need to water every 3-4 weeks on the warmer days, possibly slightly more often depending on how damp your soil remains.  You will be surprised at how warm the cold frame environments can be!

Is there a type of cold frame that you have found to work?


How to Build Cold Frames


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