Imagine going to a cold frame on Christmas day and harvesting some greens for a garden-fresh salad for the family. A cold frame is a simple structure that utilizes solar energy and insulation to create a microclimate within your garden. Planting your seeds and placing them in a cold frame can give you an early start to garden bedding plants. Placing tender plants in the cold frame weeks before the last frost can give you a great jumpstart on growth and maturity for garden plants. The plan is to create a little micro climate in the garden that is warmer than the outside air that allows plants to thrive out of season. Placing a cold frame on the ground is good protection for hardy plants like spinach and bok choy, but even greater protection can be added by digging the cold frame into the earth. Adding manure or compost under the soil in the cold frame can make it a “hot” box where the heat created by the composting helps heat the structure. A man in Utah, digging down a few feet, was able to create a cold frame that allowed him to grow citrus fruit. Yes, citrus which fruits in the middle of winter.

Rosemary Murray, up the hill a bit in Bountiful, has tended a cold frame for about three years now. She loves planting greens in the early fall so that they are mature by the time that days shorten and cold arrives. The greens then stay in a kind of stasis that allows you to eat them throughout the winter. When spring arrives in March, they begin to grow bountifully again. She marvels at “the variety of greens available, that I have never really heard of before.” She plants a variety of lettuces, spinach and Brussel sprouts. Mizuna, a Japanese green with beautiful lacy leaves and crisp, delicious stems is one of her favorites. This year, the snow has made tending her cold frame more difficult. Although it is in a protected area, it has frozen shut this year on occasion and the deep snow makes it more difficult to access. She occasionally cleans any snow off it and throws some snow in with the plants to water it. Even with a little neglect, she still has greens currently growing in it.

Rosemary notes that cold frames can be too hot when the sun and long days come. Venting the cold frames becomes vital in this weather to avoid cooking your plants. A block between the top and box can be adequate ventilation. Her brother, Bruce, has a pear tree that gets leaves just as the cold frame needs a little sun protection and then looses its leaves just as more sun is needed to keep plants growing into winter. More information on growing crops year-round in Utah is available on the Utah Gardeners Facebook page. Rosemary said that some year-round farmers sell greens at the Gateway Mall Farmer’s Market.

Choose a sunny location for cold frames usually on the south side of the house. Frames are usually tilted at an angle to take advantage of the lower-lying winter sun. They can be placed on a patio, driveway or directly on the soil. Usually, 6-10 inches of good quality planter soil is sufficient. Rot resistant wood is good for the frames and plastic/plexiglass makes a lightweight lid. Old windows and scrap wood can also be used. Placing some scrap pieces along the bottom can protect the box from rot over time. These pieces can be replaced, rather than the whole frame, when they begin to deteriorate. Some gardeners cover their whole garden box beds by stretching plastic over a curved frame. Even a milk bottle placed over a plant is a miniature cold box. If an unseasonably cold night occurs after tender plants are already growing, a blanket can be thrown over the cold frame for extra insulation. Additionally, gallon water jugs painted black can be placed in the bed to absorb heat during the day and releasing that heat to the box during the night. Planting a garden in Utah can be enhanced by including a cold box to lengthen the season. λ