Here is the plan drawing that we used for the four raised beds:
The basic raised bed is 7' x 4' and is constructed using 2 x 12 cedar boards with 4 x 4 cedar post in each corner (Note: Cedar is one of the best choices for wood that will be in contact with soil).
Pine sides fit into position like a jigsaw puzzle to transform the raised bed into a cold frame each fall. (Note: The cold frame box does not touch the soil and so we opted to build it with less expensive pine.)
Here you can see a photo showing all the sides in position without the obstructed view with the top in place:
Because the sides fit together like a puzzle no nails are required to hold them in position. Any one of the side walls can be removed in a matter of minutes.
The final stage of the fall transformation from raised bed to cold frame
involves the installation of three plexiglass doors.
1. Here you see the first completed cold frame door in position. We opted to use plexiglass for the doors rather than glass because it is not as breakable. Also for amateurs like us, plexiglass was a lot easier to work with!
We were able to get readymade plexiglass panels (30" x 60") at the Home Depot which were almost the perfect size. We just had to shorten each plexiglass panel by 6 inches.
The door frames were made using four pieces of 1 x 2 Pine. To construct the door frames cut 2 x 54" lengths and 3 x 26.5" pieces (the competed door width will be 30").
2. The construction of the doors is very basic. Simply screw L-brackets into place at each corner of the door. The window's centre support bar is held in position with a metal T-bracket at each end. Then finishing nails are added at each corner for extra stability.
We designed the plexiglass panels to sit on top of each door frame rather than being inset (as in a standard window frame). We wanted any rainfall or snow to be able to slide cleanly off the surface of each door.
Now place your plexiglass panel on top of the frame and clamp it into position. You need to cut off the extra 6" overhang. Using a T-square and an Exacto knife score the plexiglass along the outside edge of the frame. Hubby carefully scored the line 6 times to ensure a good clean cut.
4. Grab a scrap of wood and place it along the inside of your scored edge. Now press down on the overhang and it should snap cleanly free.
5. Attach the plexiglass to the frame with 3/4" #8 Robertson screws (3/4" Phillips will work just as well). We placed a screw approximately every 6.5".
Just a couple more steps!
6. Now attach a handle to the centre front of each door. We used an inexpensive 5 3/4" handle.
7. On the back on the cold frame attach each door with two 3.5" T-hinges approximately 6" in from the sides of each door. These T-hinges are the one semi-permanent part of the cold frame that will have to be removed to dismantle the cold frame each spring.
Condensation on the inside of the plexiglass doors provides plants with moisture.
The cold frame is not heated of course, and so during the winter it will get cold in there, but the enclosed structure will always be much warmer than the surrounding environment.