Day 12: Get Your Vegetable Garden Growing with a Cold Frame

One way to extend the vegetable growing season — both on the front end in spring and on the back end in fall — is to use cold frames, hoophouses and other simple forms of protection for your plants. A cold frame is basically a mini-greenhouse for acclimating seedlings you started indoors or growing tender plants when the weather is still too cold.

cold frame with lettuce

Lettuce and other greens grow well in a cold frame early in the season.

Most cold frames have solid sides (wood or cement block or straw) to block wind and some kind of a clear cover (glass or plastic) to let light and heat in. The cold frame should have a system so it can be opened in the day so the plants don’t get too hot and then closed up again at night. Cold frames should be placed in the sun, but many gardeners also like to put them up next to the house so they pick up some residual heat. You can also put a cold frame right on top of a garden bed to act as a temporary greenhouse. Most gardeners use them to harden-off seedlings or hold cool weather plants until it’s time to put them in the vegetable garden.

There are lots of videos showing how to make a cold frame using an old window, some pretty complicated woodworking tools, or PVC pipe and plastic.  No need to buy a premade cold frame — use your creativity. The photo here shows a cold frame used outside of the MSHS office in Roseville. It’s a simple wood box with a corrugated plastic top. The plastic is attached to wood pieces and hinges connect the top to the box, so it can be easily opened in the day. Because the plants and wood absorb heat during the day, it’s possible to leave cold-weather plants (such as lettuce) outside even on pretty chilly nights.  (If it gets really cold, throw a blanket over the cold frame for extra insulation.) According to garden author Eliot Coleman, the temperature inside a cold frame can be up between 7 and 20 degrees warmer at night than the temperature outside.

If cold frames help extend the garden season and are so easy to make, why don’t more gardeners use them? One reason may be that you really do have to keep an eye on the cold frame and the weather. If it gets suddenly warm and sunny and the lid is down, your plants could be in tropical conditions very quickly! Also, you don’t want to forget to shut the cold frame on a cool night. But if you want to harvest lettuce early and be one of the first people on the block to pick a tomato, a cold frame is a great vegetable garden investment.

Do you use a cold frame? How have you set it up?






  1. […] and reliably indoors under lights. You can also plant lettuce seeds directly in your garden or in a cold frame, but you may have to wait a bit for germination since lettuce requires a soil temperature of 40 […]

  2. […] experienced gardeners sow their lettuce and other cool season crops under lights indoors (or in a cold frame) then transplant them outside once they have a few leaves and are growing. At that point, the cool […]

  3. […] in Nova Scotia 12 months a year. The secret to so much abundance is careful use of covers. She has cold frames for hardening off vegetables and a series of plastic covered hoops for giving seedlings a good […]

  4. Succession Planting in the Vegetable Garden on July 21, 2021 at 3:06 pm

    […] and greens started as soon as possible, even indoors. As discussed in earlier posts, using a cold frame as a holding spot for trays of greens makes for earlier planting, and allows you to be harvesting […]

  5. […] northern gardeners often use cold frames to give seedlings a jump start in spring, adding a cold frame to your garden can be helpful in fall, too. Positioned to catch the […]

Leave a Comment