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How To Use Cold Frames In Your Garden

By Staff Writer
Share to PinterestHow To Use Cold Frames In Your Garden
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In areas with early frosts, it’s a challenge to grow fruits and vegetables that require a long growing season. Cold frames can make all the difference. These miniature greenhouses warm the soil and protect plants from frost. Basic cold frames have wood sides and a glass top that traps the sun’s heat during the day. These moveable heat catchers sit directly on your garden beds and can be placed wherever your plants need a little extra warmth.

01

Benefits for northern gardeners

Where the winters are long, cold frames can help you get a jump on seed starting in the spring. As soon as you can work the soil, place the cold frame on the bed to trap heat and help your seeds germinate. The frames will also protect delicate seedlings from late frosts and hungry rabbits until they’re ready to transplant. In the fall, cold frames extend your harvest of hardy greens and root vegetables by keeping a killing frost or hard freeze at bay.

Share to PinterestMan sitting working on diy project construction closeup of vegetable winter garden for raised bed cold frame box in Ukraine dacha by farm house
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02

Types of cold frames

Traditional cold frames have wooden sides and a glass top that can be raised to access plants and propped open to let out excess heat. The most popular design is a "lean-to" shape, which evolved from cold frames originally built to lean against the side of an existing greenhouse. The back of the lean-to frame is taller than the front, creating a slope for the glass lid. Portable cold frames are built with lighter-weight materials like plexiglass and aluminum.

Share to PinterestA beautiful set of cold frames filled with plants ready to go out in the summer borders.
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03

Where to place cold frames

To best hold in the heat of the day, cold frames should be placed in garden beds with full sun during the early spring and late fall. Ideally, the slope of the lid should be angled toward the south to take full advantage of the sun’s rays, but you can also get good results facing a cold frame to the west or east.

Share to PinterestPanorama cold frame in the garden
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04

Easy cold frame construction

If you’re handy, all you need to build a cold frame is some lumber, galvanized screws, and some old windows. Build the wood frame with a back that’s twice as high as the front, and cut a slope on the side pieces to connect them. Once that’s screwed together, you can use an old window for the lid. You can also build a frame to hold a piece of plexiglass if you don’t have an old window available. If you don’t have tools, you can “build” a frame of straw bales and place windows on top.

Share to PinterestWoman building raised garden beds in backyard on summer afternoon
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05

Preparing the garden soil

As soon as you can work the soil in early spring, rake in compost and a balanced fertilizer, making sure to loosen the soil at least a foot down. If the ground is frozen or muddy, you can place the cold frame on the soil to help warm and dry it, but don’t plant anything until you can turn the soil easily.

Share to PinterestCropped shot of feet digging a patch over with a garden fork
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06

Starting spring seeds in cold frames

Before sowing seeds in your cold frame, moisten the soil well and allow it to drain for several hours. The goal is to plant in moist, not wet, soil. Place seeds according to the packet directions for depth and spacing. Gently pat the seeds into place and lightly water again. Keep the cold frame cover on tightly until germination, when you can vent as needed on warmer days. Check the soil daily for dampness and water when necessary—you don’t want it to dry out.

Share to PinterestA 3-year-old child helps his parents grow vegetables in the country.
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07

Hardening off cold frame seedlings

Share to Pinterestbrick built open cold frames with flowers

Plants grown in a cold frame are used to warm conditions, so they need to acclimate to the outdoors as the temperature warms. A couple weeks before your last frost date, begin taking the lid off the frame for a few hours each day, gradually increasing the plants’ exposure to the elements. Once nighttime temperatures are above freezing and plants are acclimated, you can remove the cold frame entirely.

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08

Fall planting in cold frames

For a crop of fall veggies, plant seeds or transplants in your cold frame near the end of the summer, but keep the lid off. As nighttime temperatures drop, place the glass lid on the frame a few hours before sunset. Eventually, you’ll keep the lid on all day, venting only as needed. This will help plants survive many weeks beyond the first frost date in the fall and even into early winter for an extended harvest.

Share to PinterestMan working on diy project construction closeup of vegetable winter garden for raised bed cold frame box in Ukraine dacha by farm house
krblokhin / Getty Images

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09

Managing cold frame temperature

When using cold frames, it’s important to keep an eye on daily temperature fluctuations to keep your plants under optimal conditions. When temperatures rise above 60 degrees, you’ll need to remove the lid to keep them from burning in the sun—the glass acts like a magnifier. When temperatures fall below 40, close the lid again, ideally before the sun sets to trap the last heat of the day. In between 40 and 60, prop open the lid to split the difference.

Share to PinterestCold frame of organic vegetables and salad leaves growing in a wooden frame to give protection from the cold winter frost weather and from slugs and snails who may eat the crop, stock photo image
TonyBaggett / Getty Images

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10

Best cold frame crops

You can start any kind of seeds you like in a cold frame before transplanting to elsewhere in your garden. For plants you wish to keep warm in the fall, leafy greens and root vegetables work best. Consider cold-hardy varieties of lettuce, arugula, spinach, and kale. Carrots, turnips, parsnips, and bok choy are also excellent choices for a cold frame garden. Just be sure to check plant height so they don’t hit the lid.

Share to Pinterestcarrots and cabbage on the soil in a vegetable garden
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