How to Build a Cold Frame

Get an early start on spring planting or extend your gardening season with this DIY cold frame. A type of “mini-greenhouse,” a cold frame built with a glass or plastic lid allows plants access to sunlight and traps heat to prevent cold weather from putting an early end to your new crops. Follow these simple steps to construct your own cold frame using just a few tools, lumber, and a reclaimed window frame. The addition of a temperature-sensitive foundation vent will keep air flowing without risking plant loss due to unexpected cold snaps.

You will need: reclaimed 24-inch x 48-inch window (check window replacement shops, thrift and antique stores) / 2-inch x 8-inch x 16-foot rough cedar plank / one foundation vent / twelve 4 1/2-inch lag screws / two 3 1/2-inch galvanized T hinges / 8 hinge screws / two 4-inch eye hook latches / tape measure / drill with pilot bit and screwdriver tip / circular saw / straightedge / c clamps / jigsaw

From cedar planks, measure and cut three 48-inch lengths, two 18-inch lengths and one 20-inch length. These will be used to construct a simple raised bed and a second-tier angled cap to which the hinged-lid window frame will be attached. This project uses a 24-inch x 48-inch reclaimed window, but may be adjusted to accommodate windows as large as a storm door by matching the box size to window size. A larger cold frame may benefit from the addition of a second vent.

Cut the 20-inch cedar plank diagonally from corner to corner. C clamps and a long straightedge can be used as a saw guide, but are not required. These two pieces are the sides and will support the lid at a sloping angle to maximize sunlight.