This cold frame is meant to be used on top of a 4' x 4' raised bed. When in position the cold frame will trap heat from the sun to warm the soil in the bed. By trapping the heat you can start your cold-tolerant crops much earlier and extend your gardening well into the Fall. The frame must be monitored because a sunny day can cause the temperature inside to get hot enough to kill the plants. By simply raising one side of the frame you can insure that the temperature won't get too hot.
2- 2" x 3" x 8' boards
8- 2-1/2" #10 screws (I prefer hex head)
2- 1/2" x 10' PVC pipe
6' x 8' - sheet of heavy plastic (don't trim too closely yet)
2- loose pin hinges and screws
10'- 1" wide chipboard strip (cut from a cereal box, for example)
Safety glasses & hearing protection
Saw (hand crosscut or circular)
Power drill and bits
Drive bit for screws
3/4" spade drill bit
Box cutter or sharp knife
Stapler and staples
Workbench with vise.....helpful but not necessary
Sawhorses.....helpful but not necessary
Step 1: Parts Prep and Assembly
1) Cut the 2" x 3"s into four 48" long pieces and drill two pilot holes about 3/4" from one end of each 48" board. These holes will help prevent the boards from splitting.
2) Lay the boards in a square on a flat surface so each pair of screws will go into the end of the board next to it (first and second pictures).
3) Install the screws so all of the boards are securely connected in a square.
4) Cut the PVC pipes into 5' long pieces
5) Use the spade drill bit to drill holes into, but not through, two opposite boards as shown in the third picture. These should go in right at the top, inner edge at about a 55 degree angle. See the third and fourth pictures. Drill holes at the other ends of the same boards. For a 4' x 4' frame the other holes should be about 15" from the end holes.
6) Insert the ends of the PVC pipes into the opposing holes as shown in the fifth picture.
7) If you have sawhorses, put the frame with the installed PVC (hoops) on them. Put the plastic sheet over the hoops so it hangs below the wooden frame on all sides. Staple the plastic in place in one corner. Align and tighten the sheet and put in another staple at the other end of the same board. Align and straighten as you secure the other side of the sheet with staples at each end. Now go back and staple the plastic with the chipboard strip on top of the plastic. The strip will help prevent the staples from tearing through the plastic. There should be a staple about every 8" apart.
8) Leave plenty of plastic at the open ends of the cold frame. You can use the extra plastic there to securely close the ends on cold nights.
9) Set the frame on top of the 4' x 4' and install the hinges.
10) Make sure you have a couple bricks or pieces of wood to block the frame up on warm days.
11) As cold weather passes, remove the hinge pins and store the cold frame for use later in the Fall as the temperatures drop.