How to Build a Cold Frame

Ever since noted organic farmer Eliot Coleman published his book "Four Season Harvest: Organic Vegetables from Your Home Garden All Year Long," cold frame gardening has been growing in popularity. A cold frame is a raised bed with a transparent lid that allows sunlight to penetrate. The lid is raised or lowered to control the temperature inside the box or raised bed in order to extend the growing season.

Difficulty:

Moderately Challenging

Instructions

1. Pick a sunny, preferably sheltered spot in your yard in which to build your cold frame.

2. Decide on the dimensions for your cold frame. Popular dimensions are 3 feet by 6 feet or 4 feet by 8 feet. The height should be at least 8 inches, with 12 inches being better. Keep in mind that if you are small framed yourself, it may be difficult to reach the middle of a 4 foot-by-8 foot bed when seeding or weeding.

3. Measure and cut two sides and two ends for each cold frame from untreated lumber. Fasten the ends to the sides using galvanized L-brackets and galvanized screws.

4. Reinforce 8-foot sides at the 4-foot point by pounding a wooden or metal stake into the ground immediately abutting the side boards to increase rigidity. Reinforce 6-foot sides at the 3-foot point.

5. Add shims to the top of both ends that angle from a maximum height of 1 inch at one end gradually tapering to a minimum height of a 1/2 inch at the opposite end. This will allow precipitation to shed off the lid during bad weather.

6. Make two lids per cold frame with a width to match the cold frame and a length half that of the cold frame from untreated 1 inch-by-3 inch untreated boards. Eliot Coleman has plans in his book that call for super-expensive rigid plastic. For a less expensive--albeit less durable--alternative, use heavy-duty plastic film sold in fabric stores as tablecloth covering material. Cut the plastic 3 inches larger on each side than the lid frame, and staple it to the frame with heavy duty galvanized staples. The plastic should be taught when you are done stapling. When done, the lids simply rest atop the cold frame itself so you can easily remove them when you need to seed, weed or water your garden.

7. Fill the raised bed with soil and any organic soil amendments you plan to use, and you are ready to begin using your cold frame.

Tips & Warnings

• You can grow in your raised beds year round. The timing of when to use your cold frame lids will depend on what zone you are in. For example, in zone 5, the cold frame lids will likely be used from October or November through April.

• The purpose of the cold frame lid is to maintain an ambient soil and air temperature that encourages plant growth and protects the plants from freezing.

• Chemicals from treated lumber will leach into your soil, contaminating it and your produce. Build your cold frame from untreated lumber only. Cedar is the preferred choice thanks to its natural weather resistance, but it is expensive. A less expensive alternative that offers almost the same benefit is hemlock.

• It is possible even during winter that the temperature in a cold frame could get high enough to stifle the plants. You must remember to prop the cold frame open a little to allow for venting on days when overheating is a risk.

• The cold frame will expedite the evaporative process that naturally occurs with soil. Be sure to check soil moisture and keep your beds properly watered.

Resources

• Amazon sells Eliot Coleman's books.