Cold Frames

I made another cold frame yesterday, using the same design I’ve used for the last several ones I’ve made. They are 4 feet by 4 feet square, about 8 inches tall in front and tapering to 12-1/2 inches in back.

This size is perfect to fit the beds around my greenhouse, which are about 3-1/2 feet wide. And the height is tall enough for what I usually grow in those beds, things like lettuce, spinach, Asian greens, radicchio, endive, and kohlrabi. It’s also tall enough to protect early plantings of broccoli and cabbage.

What follows is not intended to be a step by step tutorial on how to build these cold frames, but I’ll try and give enough details so that anyone with basic carpentry skills could adapt them to fit their own needs.

cold frame base (click on any photo to enlarge)

The base is made of 2″ thick untreated dimensional lumber. I’ve made cold frames from exterior plywood in the past, but I find the lumber is easier to work with. Plus, if I get the pieces in 8 foot lengths it works out well for the 4×4 foot overall dimensions of the cold frame. The front piece is a 2×8, and the back is a 2×12. The side pieces are 2×12’s cut using a circular saw to slope from 7″ at one end to about 11″ on the other end.

2×3 corner blocks

The corners are reinforced with a short block of 2×3 lumber. The side pieces are screwed into the blocks with #8 exterior 2-1/2″ screws. I drill pilot holes for all the screws used for the sides. Then I use my cordless drill to screw them in.

2×2 lumber on base

Once the base is assembled, I add a strip of 2×2 lumber to the bottom of the base lumber pieces. That keeps the side pieces from sitting directly on the ground, which means the 2×2 pieces should be the first thing to rot. It is easy to replace the 2×2’s, and it is cheaper than replacing the larger lumber. It also adds about 1-1/2″ to the height of the cold frame. The 2×2 strips are screwed to the base using the same exterior screws used before.

top for cold frame

The top is constructed of 2×3 untreated dimensional lumber. I lay out the pieces on a flat area, using a simple butt joint. Then I use angled and flat corner braces to join the pieces together. I don’t use any additional nails or screws in the top pieces.

closeup of corner braces used on top

The top construction is quite adequate for my lightweight covering materials, which are usually polyester row cover material or plastic poly sheeting. Another design would be needed for plexiglass or glass covered tops.

hinge detail

I use two 3-1/2″ or 4″ hinges to secure the top on the base. No need to mortise the hinges – this isn’t fine cabinetry work. The screws that come with all the hardware are adequate for my needs.

handle for sides of cold frame

I like to add a couple of handles to the sides. That makes it easier to move the rather heavy cold frame around.

row of cold frames along side of greenhouse

Here’s a photo of the new cold frame in place next to the two older ones. I bought enough materials to make one more frame, which should be all I need for the time being.

another shot of cold frames

The last step is to add the cover material. In this case I’m going to use Agribon row cover material, stapled to the top.

If you’re not using cold frames, you might want to give them a try. They are a great way to to extend your growing season. They’re easy to construct, and fairly inexpensive to make. The materials for this one cost about $35 per cold frame, and I put it together in a little over two hours.

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7 Responses to Cold Frames

  1. Robin says:

    Very very nice job…..I think that I’m just going to take the tops off of mine when the weather gets nicer. We have absolutely no place to put them for the summer and I need the beds for summer veggies too

  2. Mike says:

    Very well done, I might have to copy your design as I need a cold frame like this to grow our corn mache in and yours looks like it would work splendidly. The last one I made was a little too large for my needs.

  3. Lisa says:

    Villager, I plan to copy your cold frame design using the Agribon cover. Thank you for sharing! I notice in the photo above that one of your cold frames appears larger than 4 x 4, but you say 4 x 4 is your preferred size. Do you mind sharing some of your reasons? Is it that the covering sags at the larger size? Or maybe the 4 x 4 size is easier to move around? I suppose the Agribon provides season extension rather than winer harvest.

    • Villager says:

      Lisa, all the ones in the photos that I made are 4×4. I chose that size because my beds are 3-4 feet deep, and because if I make it 4×4 I can use 8ft lengths of lumber more efficiently. I have made cold frames in different sizes. And if the covering sags, you can always put in a cross piece of lumber to support it.

      Actually, that Agribon cover allowed us to have greens all winter. I had lettuce, tatsoi, komatsuna, spinach, and arugula in the cold frames and they all survived our winter. We don’t usually get that much snow, so the Agribon material is enough for a cover. And it doesn’t heat up rapidly during the day like a plastic or glass covered frame.

      Thanks for stopping by!

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  5. Echo Wu says:

    Hi Dave,

    When should we cover up the cold frame to protect the autumn / winter vegetables? Is it after the first hard frost? I live in Hudson Valley (zone 6a). This is the first year I am growing a vegetable garden. My husband has just built a cold frame for me with an old storm window I have obtained from Craigslist. Thanks!

  6. Dave says:

    Yes, you want to have the cover on after the first frost or freeze. And you will need to open the cover on sunny, warmer days.

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