by Sarah Gardner
PR/Marketing Manager at Texas Discovery Gardens

With winter temperatures dipping and diving daily in North Central Texas, it can be hard to keep winter vegetables growing. With a day’s work and about $40, you can build a cold frame to protect seeds and vegetable starts when it does get close to freezing.

Capturing the Sun’s Energy

A cold frame is a miniature greenhouse, an angled wooden box with a clear plastic top on a hinge. Texas Discovery Gardens’ Director of Horticulture, Randy Johnson, has built several to fit over small garden plots throughout the EarthKeepers Vegetable Garden.

The cold frame captures the sun’s energy and warms both the soil and air within it. As night falls, the warmer soil releases that heat, keeping plants warmer by up to 10 degrees or more. With the top of the cold frame closed during the day, temperatures can rise by 20 degrees or more. If it warms up too much, prop the lid up to allow air to flow through and cool it down. A cold frame also acts as a wind break, reducing the amount that the soil will dry out.

Making and placing a cold frame

The cold frames at Texas Discovery Gardens are made of cheap materials that can be scavenged or found at home improvement stores. They measure four feet by four feet and have held strong through the last three winters. One eight foot by four foot sheet of plywood creates the side walls of one cold frame. While glass or Plexiglas would work for the lid if you have some on hand, Johnson used cheaper 3.5 mm plastic sheeting. See step-by-step instructions on how to make a cold frame, courtesy of Texas Discovery Gardens’ Director of Horticulture, Randy Johnson, here:  http://texasdiscoverygardens.org/Cold_Frame.pdf

When placing your cold frame, look for a flat area in your garden. To maximize solar potential, angle the cold frame with a 15 degree slope and a southern exposure.

Winter’s Bounty

You can plant directly into the soil or place seeds or 4-inch starts within the frame. Then, once you “harden off” the plants, or get them acclimated to the weather, you can plant them in your normal garden beds and start a new crop in the cold frame.

Find details for Texas Discovery Garden events at http://texasdiscoverygardens.org/events_and_classes.php.

Good winter and early spring vegetables are carrots, bok choy and other greens, onions, beets, radishes, and turnips. As Johnson encourages, look for your favorite winter veggies in the store, and grow the most expensive ones by seed. You’ll save money and enjoy that organic, fresh taste that only comes from home grown veggies.