Cold Frames: What They Are and How To Use Them

Oh, the hubris in that title!

For the truth is, I am only a beginner when it comes to cold frames.

For eight years, I have thought about asking my husband to build one for me. I have even gone so far as to mention the idea from time to time, but I never took the step of sending him links to “diy cold frame tutorials” because I was never quite sure how to use them in my harsh winter / summer climate.

Were these tools perhaps best left to the English gardeners with their mild climate and cool summers? I feared that a cold frame would be insufficient in January and altogether too much in July, so why bother?


First: What is a cold frame?

It’s a bit like a small, unheated greenhouse.

A four-sided box is open on the bottom and topped with a removable pane of glass or clear plastic. The box can be placed on bare ground or on top of a raised bed. When the glass is lifted, seedlings and other vulnerable plants can be protected inside.

Second: How are they typically used?

Cold frames are used to protect plants from damaging weather: typically, cold and wet and wind.

They can be used to harden off seedlings as they help acclimatize them to outdoor conditions. Cold frames make a good way station between indoor growing lights and the outdoor garden. They can also be used to hold cold-hardy annuals like sweet peas that have been sown in fall but won’t be planted out until spring. This gives cool-season plants a head start.

Cold frames can protect potted bulbs from too much wet during the winter. They can also hold small plants grown from cuttings until they have grown enough to be planted out in the garden.

They can also be placed directly over soil–in the ground or in a raised bed–and seeds sown within, providing a protected environment for lettuces in cold weather, for instance.

Third: How will I use my cold frame?

No doubt I will learn through trial and error, but here are some of the ways I am already using my cold frame and how I intend to use them (yes, we are already building a second!) throughout this growing season:

  1. For growing trays of cold-tolerant seedlings like peas, sweet peas, violas, and pansies in order to save space under my growing lights for less cold-tolerant plants
  2. For hardening off all of the seedlings before planting them in the garden
  3. For holding pots of daffodil and tulip bulbs all winter, giving them some protection from cold and wet.
  4. For extending the season when I can grow salad crops: I will place over a raised bed and sow seeds directly
  5. I will remember to ventilate my cold frame–propping the top up on warm days–in order to circulate air and keep my plants from being burned


It’s true that I might not use my cold frame year-round here in my zone 6 Pennsylvania garden. July and August are probably too warm to ever need a cold frame, but I am beginning to understand how I might come to rely on a cold frame–or two, or three!–the other three seasons of the year.

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Posted on

March 15, 2021

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