How to Build a Cold Frame

A DIY cold frame can be constructed in several different ways. Some cold frames are made with upcycled window frames. Others look like tiny tents and sit on top of your plants. For this project, you will use wood and sheets of plastic to build a cold frame.

Tools:

• Circular saw or table saw
• Drill with 1/8-inch bit for pilot holes and driver bit for screws
• Pencil
  
• Hammer or mallet for chiseling
• Tape measure
• Straight edge
• Rafter square
• Sharp chisel
  

Materials:

• Two 2 x 6 x 8 cedar boards
  
• Two 1 x 4 x 10 cedar boards
  
• (16) 3-inch exterior stainless steel screws
  
• 2 stainless steel hinges
• 1 stainless steel handle
• 3/4-inch stainless steel exterior screws (if not provided with hinges and handle)
• Exterior wood glue
  
• 24 mirror clips
  
• Six 8- x 10-inch pieces of clear plastic
  

Below is the cut list for building the cold frame pictured above.

• Measure and cut the two 2 x 6 x 8-foot cedar boards. Cut three pieces at 24 inches and cut three pieces at 33 inches. These will be the sides of the cold frame.
• Measure and cut the two 1 x 4 x 10 cedar boards to three, 36-inch long pieces and four 24-inch long pieces. These will be the top and base of the cold frame.

This cold frame will be 36 inches wide in the front and back. Each side will be 24 inches wide. To make the base of the cold frame, arrange the parts so that the outside measurement of the frame is 24 x 39 inches.

• Lay the two 36-inch pieces of wood parallel, about two feet apart. They will serve as the front and back of the cold frame.
• Place the 24-inch pieces of wood on either side of the two 36-inch pieces to make a rectangle.
• Use 3-inch screws to connect the side pieces to the front and back pieces.

Make two wedges, one for each side of the base cold frame. Diagonally cut one of the 24-inch long board pieces. These wedges will allow the top of the cold frame to slope downward so any rain can run off the cold frame.

• Make sure each wedge fits by placing each one on top of each side. The thicker side should be in the back and narrower one in the front.
• Drill two pilot holes in each wedge.
• Use the 3-inch screws to firmly attach the wedges to each side of the base.

Lay out the cold frame top so it looks like a window pane.

• Lay out the four, 24-inch 1 x 4 wood pieces for the window top frame.
• Place the 36-inch boards horizontally.
• Place the 24-inch boards vertically across the 36-inch boards.
• Use a square to make sure the wood pieces are properly placed.

Tip: Make sure the space between each pane are smaller than the 8 x 10 clear plastic "window" panes.

Use half-lap joints to put the cold frame together. A half-lap joint is an indention in a wood board that creates a strong, snug fit.

• Carefully measure and mark the half-lap joints.
• Cut the half lap joints by setting your saw’s cut depth to half of the material’s thickness. For example, half of 3/4-inch is 3/8-inch.
• Make multiple vertical cuts through each joint to make chisling easier.

Use a sharp chisel and hammer to hollow out a flat surface for each half-lap joint.

• Clamp the wood firmly to a stable surface.
• Position the chisel with the beveled side facing down.
• Working with the grain, use shallow cuts to remove the extra wood.
• Chisel from the edges toward the center.
• Use the flat side of the chisel to scrape and smooth the surface.
• Periodically, use a square to check for high spots.

Safety Tip: Keep your hands behind the cutting edge for safety.

Once you have the parts of the top of the cold frame cut and in place:

• Glue the 36-inch wood pieces to the 24-inch pieces to make the panes. Gluing the wood will make a nice flush cover for the cold frame.
• Clamp each joint as you glue.

• Drill a hole in the corners and in the center of the sides of each of the 8- x 10-inch plastic panels. You will drill a total of eight holes in each one of the panels
• Place screws in the holes of each panel.
• Attach the screws to the underside of the window-pane top of the cold frame.

Tip: You can use fiberglass or glass panels instead of plastic sheeting. However, if kids or pets will be playing near the cold frame, don't use glass. It can break easily.

• Position and place the window panel top onto the cold frame base. Double check that it's aligned, the edges are even and it fits well.
• Securely attach hinges to the top panel with evenly-spaced screws.
• Once the hinges are in place on the top panel, screw them into the cold frame base.

When you’re done building a cold frame, you can add a handle to it to make it easier to open and close.

• Center the handle to the lid close to the bottom edge.
• Use 3/4-inch screws to fasten the handle to the cold frame.

Now that your DIY cold frame is complete, below are some tips for location and more.

• Put the frame in a location that gets full sun all day. Most times this will be on the south-facing side of your yard.
• Find a spot sheltered from strong winds to maintain consistent temperatures inside the frame.
• Place the frame on top of well-draining soil to prevent water pooling and root rot.
• In cooler months, use straw or mulch around the base to help retain heat.

• Raise the lid on your cold frame when the temperature hits 40 degrees Fahrenheit or above, so the heat doesn’t build up and cook your plants.
• Close it in the afternoon to trap warmth overnight.
• Use a stick to prop the lid open for ventilation on warm, sunny days. Cut notches in the stick so you can control how high to raise the lid. If needed, use a shade cloth to lower the temperature of the cold frame on hotter days.
• Don’t use glass for your cold frame if your area gets snow or ice. The build-up of snow or ice could break the glass.
• Angle the cold frame so that the back is higher than the front. This setup helps capture more light and lets rain run off the roof.
• For extra protection, place the cold frame next to a building.
• For additional insulation, dig 6 to 8 inches into the soil and build your cold frame partly below ground.
• If you’re concerned about flooding, add a layer of gravel underneath.
• When the temperatures drop to 20 degrees Fahrenheit or below, protect the cold frame by layering old blankets on top. You could also use electrical heating cables to warm your cold frame.