Crop ProtectionAs the seasons progress there are several uses for a cold frame.

• Start cool-temperature spring vegetable seeds and seedlings in late winter.

• Start summer warm-temperature vegetable seeds and seedlings beginning in early- or mid-spring.

• Start fall and winter crops under shade cover (replace the frame’s glass or plastic sash with framed shade cloth).

• Protect warm-temperature crops from an early frost before harvest.

• Protect cool-temperature and cold-tolerant crops for harvest through the winter.

• Over-winter cold-tolerant crops started in fall for renewed growth and a spring harvest.

Season-by-season cold frame operations calendar:


• Early spring (February, March, and April), sow and germinate seed of hardy and half-hardy early crops. Sow early crops in containers or sow in the soil under the frame as soon as the soil is workable.

• Hardy vegetables for cold frame growing include salad ingredients such as lettuce, spinach, kale, arugula, broccoli, cabbage, cauliflower, chard, radishes, and scallions.

• Cool-season root crops can be grown from seed to harvest in the soil beneath the frame; these include beets, carrots, radishes, and onions.

• Harden off or acclimatize seedlings to outdoor conditions in the frame after they have been started in the cold frame, hot bed, or greenhouse. Ventilate the frame to gradually expose seedlings to more and more outside air and light.

• Place the portable frame over a garden bed to raise the soil temperature and improve seed germination and accelerate the growth of seedlings.

• Late spring (April and May), after cool-weather seedlings are harvested or transplanted into the open garden, sow in the frame in paper pots tender, warm-season crops including beans, cantaloupe, celery, corn, eggplant, peppers, melons, pumpkins, squash, and tomatoes.

• Late spring, harden off in the frame tender seedlings started in the hot bed or greenhouse.

• As outside temperatures warm, do not allow the frame to become overheated this will result in weak and spindly plants. Harden off seedlings with ventilation and less watering; this will condition them to withstand the shock of transplanting

• Avoid growing cool-weather and warm-weather crops in the frame at the same time; they have different temperature requirements.


• Make first, second, and third sowings of quick-maturing, warm-weather crops for growing on before setting out in the garden. Raise or remove the top to keep the seedlings from becoming overheated.

• Remove the frame sash or lid and use the frame as a nursery bed to start fall crops or perennials from seed.

• Start root cuttings or herbs and perennials.

• Harden off tender plants started in a hot bed or greenhouse before setting them in the garden.


• Extend the harvest of warm-weather summer crops.

• Grow salad greens and other compact cool-weather crops.

• Place the portable frame over the garden bed to provide frost protection and added daytime warmth to keep late summer and cool-season crops growing.

• Sow in fall for late fall use: lettuce, cabbage, cauliflower, spinach, radishes.

• Grow hardy vegetables for winter use: cauliflower, cabbage, kale, lettuce, and spinach. Sow seeds in August or September to allow the plants to grow to near maturity before the first fall frost. Once day’s have less than 10 hours of sunlight per day, plants will stop growing but remain crisp and viable for many weeks.


• Extend the harvest of autumn crops. Hardy crops such as leeks, kale, parsley, arugula and other greens can make some growth with cold frame protection.

• Winter-over vegetables such as kale, cabbage, Brussels sprouts, and cauliflower for new growth in the spring.

• Place dry leaves or straw in the cold frame to store in winter root vegetables: beets, carrots, parsnips, and potatoes. Do not allow the soil to freeze.


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    • You can grow crops in a cold frame through the winter. Look at the articles in the How to Grow section of this site to determine the optimal temperatures for growing as well as minimum temperatures for growth of each crop. Leafy and root crops are the best choice for growing in winter. The temperature inside the cold frame will commonly be 10 to 20 degrees F warmer than the outdoor temperature. As the outdoor temperature grows colder you can add protection on the outside of the cold frame (blankets, tarps, straw, bales of hay) to keep the inside temperature in the range for plant growth. There is not a strict formula; you will learn by doing and monitoring the temperature inside and outside the frame. If you can maintain the minimum temperature for the growth of each crop, you will have success. Growth in winter will be slower because days are shorter.

Cold Frame: Extend Your Vegetable Garden Season

Making a Cold Frame