A cold frame is an enclosed box, generally made of wood with a glass lid, that provides less hardy plants, or those susceptible to frost damage, a chance to grow. It traps the heat of the sun through its grass lid, retains it due to its wood sides, and raises inside temperature by 10 to 15 degrees to provide the plants necessary warmth they require to grow healthy. This mini greenhouse provides gardeners a chance to start plants early in the season, and transplant them to the ground once the cold reduces.
Select a spot outside in your garden or yard that receives the maximum amount of sunlight every day, such as a spot with a sunny exposure. Also make sure the spot has well-drained soil, because your baseless cold frame will be placed directly over it.
Cut the plywood sheet into four 2-by-2-foot pieces with a handsaw. Cut one of the 8-foot long 2-by-2-inch boards into four lengths, each 2 feet long. Cut the other two 2-by-2-inch boards into 4-foot long pieces and keep them aside for the top.
Dry fit the plywood pieces on a level ground to form a box that is 4 feet wide and 4 feet deep. Make sure the joints between the front, back and sides are flush before attaching them together with wood screws.
Place the frame over the selected spot, with its front edge facing southward. Dig a trench 6 to 8 inches deep along the front and taper it off at the sides. This ensures your cold frame rests at an angle in the soil, with the back 6 to 8 inches higher than the front.
Lay the 4-foot long 2-by-2 pieces in a rectangle on a level surface, to form the top of the cold frame. Nail the pieces together with galvanized wood screws.
Cut the fiberglass molding in half and fit the pieces all around the edges of the top of the cold frame. Also cut the fiberglass sheet in half with a power saw so you have two 4-foot long pieces.
Arrange the fiberglass sheets next to one another over the molding, and mark spots on them where you will drill holes. Lift each fiberglass piece and drill holes over the marks carefully. Replace it over the molding and nail it in place through the hole. Add plants into the cold frame and close the lid.