Here in the Midwest, we are in this in between season: sprinter. You know, that schizophrenic season that can’t decide if it wants to be winter or spring. One day it’s 80 degrees and I’m reading to plant all the seeds and then the next it’s 40 degrees and sleeting. I wish I was exaggerating but I’m not. We’ve had both this week. Every year I know better than to get all crazy at the first sign of warm weather, but every year I still get ahead of myself and start planting too early. Who can blame me?
This year we decided to make a simple cold frame to get a head start on our spring crops. It’s nothing fancy. I’m not expecting it to last years and years, but it only cost us the cost of the plastic ($13) because we upcycled some old wood that we already had.
The purpose of the cold frame is to protect the seedlings from the frost and cold temps. It acts as a greenhouse of sorts until the danger of frost has passed. Ours is on a hinge so during the day when the temperatures rise, we open the frame and at night we close it.
We had our first rain today. I was a bit concerned that the rain would collapse the cold frame. We propped it up on an incline so the water could run off and not pool on the plastic.
- Wood: We used 2x2s. If you use larger pieces of wood you may have to use larger hinges. Choose a wood that will withstand weather elements. Ours was recycled wood which was already treated.
- Miter saw.
- Long screws
- 4 mil clear plastic sheeting. Any thinner, and the plastic will rip easier.
- Heavy duty staple gun
- Cordless drill
How to Make a Simple Cold Frame
First measure your box around your raised bed. We first cut the two long pieces. Our were 97 inches long. Then cut the short pieces. Keep in mind you will be subtracting the width of two long sides. For example, our box is 49 inches wide. The wood frame is 1.5 inches wide, so we subtracted 3 inches and cut our short pieces 46 inches long.
Next lay out your frame on top of your raised bed so you can make sure you measured everything correctly.
Drill a small pilot hole in the end side of the long pieces. This makes screwing easier.
Make sure you have screws long enough to penetrate the second piece of wood a good inch. Screw together your frame in all four corners so now you have a large rectangle or whatever size bed you have. Optional: You can do an inset hole if your screws are long enough. This helps them reach a bit further.
We also did the same thing in the middle for extra support of the frame and plastic.
Then flip over your frame and staple thick plastic to the frame using a heavy duty staple gun. Make sure you pull it tight so there is no slack.
Trim off excess plastic.
Flip it back over and square it even with your bed frame. We then about a foot from each end on one side only, screwed on two hinges. One part of the hinge should be on the cold frame and the other part of the hinge should be on the garden box.
That’s basically all there is to it. You can open it during the day if the weather permits and at night, you can close it to protect the small plants and seedlings.
We put latches on the open end of ours. It’s optional, but recommended, especially during inclement weather if your wood is lighter weight.
There ya have it. A simple cold frame to get a head start on your growing season. This particular design is not meant for large plants but instead for the early growth of small seedlings.