A Guide to Building a Cold Frame for Your Garden

When we bought our new home atop Walch’s Mountain, my honey’s Honey-Do list grew by leaps and bounds. The first thing that she wanted was a greenhouse so she could exercise her green thumb all year long but I wanted that land for a workshop, so we compromised, I built my workshop and built her two cold frames. That was the ideal solution since our manufactured home has an east to west orientation and south facing side receives plenty of sun. I built two cold frames, each one approximately 5 feet long and 3 feet deep that sit on a foundation of bricks. I placed them on each side of the rear steps, which was where she wanted her two flower beds. Once the weather warmed up sufficiently, all we had to do was lift the cold frames off the bricks which now became her flower garden borders, and her beautiful flowers were available for all the neighbors to admire. I built both of these cold frames in one weekend but for someone less experienced then I it may take them a little longer, maybe two weekends at the most. The dimensions aren’t critical so you can change them to meet your needs.

The tools that you will need to build these cold frames.

1) 3/8” drill/driver

2) Carpenter’s framing square

3) Skill saw

4) Miter box or power miter saw

Materials

Since these cold frames will be exposed to rain, sleet and snow, you should build them from pressure treated lumber and exterior grade plywood.

What you will need

1. Pressure treated 2X6’s for the front and back

2. Pressure treated 2X2’s for the framing

3. ½” exterior (CCA Treated) plywood for the ends

4. Acrylic glazing

5. #6 X ¾” RH (Roundhead), zinc-coated screws

6. #8 X 1 ½” FH (Flathead), zinc-coated screws

7. 3” zinc-coated corner braces w/screws

8. 5” T-hinges w/screws

9. L-hooks

10. Perforated steel strap

11. White exterior latex primer

12. White exterior latex paint

13. Red brick for base

The actual dimensions of my cold frames were 62” long by 37 ½” deep with a rear height of 23” and a front height of 11 ½” so the cutting dimensions that I will be giving you are based on those finish dimensions. If you are a new woodworker keep the following facts in mind when working with dimensional lumber

1. 2X2s are actually 1 ½” X 1 ½”

2. 2X6s are actually 1 ½” X 5 ½”

If you keep these facts in mind, you will be able to adjust my cutting dimension to fit your needs for the final size that you decided upon. Remember, “Measure twice, and cut once.”

Cutting list

1. 2 pieces 2 X 2 X 34 1/2” (bottom, end spreader)

2. 2 pieces2 X 2 X 36” (top, end spreaders)

3. 4 pieces 2 X 2 X 39 ¼” (lid, side framing members)

4. 4 pieces 2 X 2 X 28” (lid, end framing members)

5. 6 pieces 2 X 6 X 61” (front and back boards)

6. 2 pieces ½” plywood ends cut to shape. They are 37 ½” long tapering from a width of 23” to 11 ½”.

7. 2 pieces of Acrylic glazing, 1/8” X 31” X 39 1/4”

Steps in constructing your cold frame

These cold frames are light enough for two people to carry so they can be built in your garage or shop and then placed in position after they are finished.

1. Begin by cutting all the pieces to size

2. Seal all the pieces with white, exterior latex primer.

3. Paint all the pieces with white exterior latex paint and allow them to dry. Apply a second coat after the first coat has dried thoroughly. We want to use white paint on the insides because it will reflect the heat of the sun rays where as a dark color will absorb the heat. The reflected heat helps heat the soil which is what we are looking for in a cold frame.

4. Assemble the two lid frames. Butt joints are fine here; just make sure that the 39 ¼” pieces butt against the ends of the 28” pieces. Use one 3” L-Bracket in each inside corner to hold the frame together.

5. Lay the frames flat on the floor and use the carpenter’s framing square to check for squareness.

6. Lay the Acrylic Glazing in place and drill pilot holes at all round the perimeter. Starting ½” in from the corners, drill 5/64” pilot holes at 6 3/8 “intervals. Once you have drilled all the pilot holes, use the #6 X ¾” zinc-coated Rh screws to secure the Acrylic glazing to the frame. If you are using a drill/driver to secure these screw set the clutch at one of its lowest settings to keep from cracking the acrylic. You can always adjust the clutch for more torque if need be.

7. Measuring 6” in from the corners attach two hinges to each frame and set them aside.

8. Lay the four 2 X 6” back pieces flat on the floor and fasten the ½” plywood end pieces to them with the #8 X 1 ½” zinc-coated Fh screws. This time drill the pilot holes using a 5/64” drill bit. It’s a good practice to always drill pilot hole because you risk cracking the wood otherwise. I’ve attached a drill bit chart at the end of this article that you can use for this project and for any other project that you may undertake in the future.

9. Use two screws to attach each board to the plywood end pieces. Layout and drill the pilot holes so that each screw is 1” from the corners of each board.

10. Attach the bottom and top stretchers to the plywood ends using five #8 X 1 ¾” screws placed at equal intervals.

11. Setting the semi-assembled cold frame upright on the shop floor, attach the two front board in the same manner you attached the rear boards.

12. Position the lids on the cold frame and attach the hinges to the back boards.

13. Center and install the two screw hooks on the top board so they line up with the center of each lid. These will be the pivot point for the   perforated steel straps.

14. Center and install a #8 screw on the front of each lid. This screw will slip through the holes in the perforated steel strap and allow you to adjust the width of the opening to allow more or less ventilation as required.

15. Lay out the bricks and set the cold frame on them.

Well there you have it, a relatively inexpensive and easy to build cold frame.