Search Cold frame on the internet and you’ll find a range of designs gardeners have made to extend the growing season. We at the Washington Youth Garden are lucky to have an architect for a volunteer who also has a passion for youth and gardening! Boyd taught us how to construct a simple cold frame using a found window frame. We actually found about 10 wooden frames with corrugated plastic sheeting in a junk pile and salvaged them all to make cold frames for each of our school gardens. This is a great fall/winter project.
We took the measurements of the frame and cut the side boards to fit the frame properly. One thing to remember is that if you are doing ‘butt joints’ like we did then you need to consider that the total length of your inside boards will need to include the width of the board it will butt up against…
A butt joint is when two boards butt up against one another. We cut our short sides 1.5" shorter on each end since the short sides are butting up against the long sides. You have to take into account the extra 3" that overlap creates on the length of the short sides.
After your boards are cut, it’s time for assembly. Screw short sides on to 4x4’ posts. We used epoxy coated deck screws.
Draw a straight line connecting the corners of the top board and cut on the angle.
Assemble short sides to the 4x4 posts first. Make sure there is an inch at least of clearance at the top so the lid closes properly. Now that your short sides are complete, It’s time to attach the long sides to form the whole box unit of the cold frame!
Now that all sides are assembled, it’s time to attach the rodent-proof hardware cloth on the bottom. Flip the box upside down nail in the ½" hardware cloth with fencing nails.
We used a staple gun to hold the hardware cloth down while we secured it with fencing nails.
The hardware cloth will prevent mice from digging under the cold frame and eating your delicate seedlings. Finally, it’s time to attach the lid.
Two hinges was sufficient for our 5.5’ long cold frame. We also added some extra hardware: a chain to the outside of both ends to keep the top open, a brass handle, and a a piece of bamboo cut to keep the lid propped for ventilation.
We will dig the cold frame about 1’ into the ground for extra insulation and put some straw inside. NOTE: Make sure to position your cold frame so the sloped window faces South for the most solar gain.
We will be ready to start seedlings early in the spring and/or grow greens directly into the cold frame.