I am not absolutely sure what to do with a cold frame, but here I am building one. The man at the lumberyard cut some of the cypress I wanted for my raised beds too short, so I bought the extra, mis-cut pieces at fire sale prices. They were really too short for much of a raised bed, so I began to see a cold frame in my future.
As I understand it, a cold frame is nothing more that a mini-greenhouse (or a monster cloche, depending on how you look at it.) It is used in the spring to harden-off seedlings began indoors and to start seedlings early. It is used in the fall and winter to extend the growing season of cool-weather crops.
I am hoping it will allow me to grow mesclun in February, but I realize this is an unlikely scenario. I will settle for being able to grow mesclun in December. We’ll see. This will be a learning experience for me.
Here’s how I built mine:
1. I built a rectangular box, 4 feet long and 2 feet wide. Using glue and galvanized ring shank nails, I hammered the first tier together provisionally.
2. With the table saw set to a 30 degree angle, I made a cut along the long edge of another 4-foot board for the tall, back side where I will hinge the window for the cold frame.
3. I snapped a chalk line along the side of a 2-foot length of board, following the 30-degree angle of the top edge of the back board and cut one side piece, then another the same size. I glued and nailed this second tier together and stacked it on top of the basic box.
4. To reinforce the box, I marked and cut pieces of 2 x 2 to fit in the corners, angling the cut on the top edge of the 2 x 2’s to follow the angle of the boards and glued and screwed these “cleats” to the box corners.
5. The next step is to build the window frame. I used some old scrap pieces of moulding. I decided to use Plexi-Glass for ease of cutting and safety reasons. It was most cost-efficient to buy two pieces of the plastic, each 28″x30″ and cut them to fit the opening with a utility knife and a straight-edge (the man at the hardware store said make 7 passes with the utility knife before you snap it). I built two frames for the pieces of plastic and used small screws to attach the plastic windows to the frames (don’t screw them in too tight–they crack the plastic–ask me how I know).
6. I attached them with strap hinges. The windows are very lightweight. I hope they will hold up. I suppose it depends on whether or not the most Juno-esque of the cats tries to nap on them.
7. The interior is insulated with 3/4″ styrofoam which is then covered with whiteboard. The whiteboard is to keep the styrofoam from getting dinged up and to provide more insulation plus a reflective surface. I glued the foam to the frame and the whiteboard to the foam with construction adhesive. Then I caulked the joints.
Future post: Putting the cold frame in the garden