Cold Frame Plans

With our cold frame plans, you can start and harden off seedlings and can add weeks to your growing season. Our easy DIY plans help you improve your gardening experience.

With these cold frame plans, you can garden on sunny apartment balconies, in urban yards, or for large rural gardens. The basic structure is simple and can help protect plants for early planting.

Ours is a box about 4 feet (1.2 meters) square. The back panel is 15 inches (38 cm) high and the front is 9 inches (23 cm) with sides sloping down from back to front.

The top is covered with a sheet of clear plastic with squared off corrugation and is reinforced by a strip of molding designed to go with the clear panel. There are many choices of clear and translucent materials that are satisfactory for the top. Just remember the function is to protect the little plants while allowing the sun to shine through the top.

The clear plastic top is mounted on a frame of dimension lumber. We used 1” x 4” boards (actually 3/4 inches by 3 1/2 inches or 2 cm by 9 cm). The frame corners are simply butted together and fastened using flat steel plating with pre-drilled holes that are fastened across the joint. We used 1/2 inch (about 1.3 cm) #8 lath screws to fasten the plates. Be sure to reinforce both top and bottom of each corner. Serious woodworkers might use a glued and screwed lap joint or a mortise and tenon joint for this.

Remember to orient the top material so that the corrugations are sloped to allow rain water to run off. We attached the top and bottom of the plastic to the frame by driving 1 inch (2.5 cm) hex head gasketed screws through the plastic and brace into the frame. We used the shorter lath screws to secure the sides to the frame. Remember to screw ONLY in the valleys of the corrugated material.

The sides for our cold frame were cut from a piece of 1/2 inch (1.3 cm) construction grade plywood. Using a chalk line, we marked two adjacent trapezoids 4 feet by 15 inches by 9 inches. The two trapezoids form a rectangle 4 feet by 2 feet or 1/2 of the plywood piece. We then marked two rectangles, one measuring 4 feet by 9 inches and the other measuring 4 feet by 15 inches. The two trapezoids are the sloping sides of the box and the rectangles are the front and back.

From a 4-foot-wide roll of metal window screen, we cut a piece 54 inches (137 cm) long and stapled this to the bottom of the box. The excess length was overlapped and stapled to the sides for additional strength. We chose the screening because we had it on hand. Hardware cloth or any strong mesh that will keep mice and gophers out and let water drain will work. We suggest a material not prone to rusting such as aluminum or galvanized metal.

Following our cold frame plans to strengthen the box, we cut four pieces of scrap wood from a piece of 2 inch by 2 inch fir. Two pieces were cut 8 inches long and two were 14 inches. The corner braces were clamped to the front and back pieces and screwed in place with 1 1/2 inch (about 4 cm) sheet rock screws that we always have in our shop. Any wood screw of appropriate length will work for this. We then clamped the sides to the corner braces and screwed them into place. This completed our basic box.

After the bottom mesh was secured, we attached the top by affixing the hinges at the back or higher end. We placed the hinges approximately 1 foot (30.5 cm) in from each side. We used a hook and eye to secure the front of the top in the closed position. We placed our cold frame in front of a south facing porch post for securing the top in the fully open position.

For venting, a variety of options are available. (read more on venting) Commercial automatic venting systems are available. An adjustable system may be installed for manual temperature control. There are many ways of propping open a top, including just using a piece of scrap wood under the front of the top with a rock on the corner for weight. Use one that is easy, convenient, and secure enough to avoid damage from spring winds.

Tools and Material for Cold Frame Plans

The building process for our cold frame plans required about five hours with simple materials and some basic hand tools.

Tools we used included:

  • Electric hand drill screw driving head
  • Hammer Heavy stapler with 1/2” staples
  • Chalk line
  • Power hand saw
  • Clamps Tape measure
  • Phillips screw driver
  • 1/4" nut driver for gasketed screws

Hardware we used for the project:

  • Hinges – 2 @ 2” x 3” hinges (galvanized or brass avoids rust)
  • 1 1/2 inch sheet rock screws – about 40 of these
  • Flat steel corner reinforcement – two per corner – 8 pieces
  • Appropriate screws for corner reinforcement and top construction
  • Hook and eye – 2 sets

Material we used for the project:

  • 1 piece of 1/2 inch CDX (construction grade) plywood – 4 feet by 4 feet
  • 1 sheet of corrugated plastic - 26 inches x 8 feet (66 cm x 2.4 m)
  • Corrugation gasket for top and bottom – enough for 8 feet
  • Aluminum screening (1/4” hardware cloth optional)

In our desert region of southern Arizona, where the sun can be strong, we built a second top frame for our box and covered it with shade cloth. This enables us to start seedlings for summer and fall rotational plantings without frying the tender little plants.

With our basic cold frame plans, you can build an inexpensive and durable shelter for your young plants. Modifications can easily be made to suit your local requirements. Happy Gardening!!

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