Building a Cold Frame!

One of the luxuries of the early spring for the hobby gardener is that this isn't a particularly stressful time. with 2-3 hours of investment, at most, per week, it's relatively easy to be right on path. I keep the light on over my seedlings, water about every other day, plant the seeds I need, and generally keep things going. Perhaps the hardest thing is keeping the temperature in my house consistently warm enough for new seeds to germinate. The ground cherries I just planted, which are a nightshade - a relative of the tomatillo - require fairly warm temperatures to germinate. With frosts still rolling through the region every few nights and with wamr sunny days, my indoor temperature is in a constant state of flux which averages around 55*, not the ideal 70, but still workable. Heat mats, unfortunately, make for a more expensive tomato than I am willing to dish out for. Maybe next year I'll finally dish out the cash for a few.

I decided that i will bring out the cold frame for my calendula this weekend. The process of moving seedlings from an indoor seed-starting set up to a cold frame is called "hardening off." I typically do it 2-3 weeks before transplanting. It's a step between the total ease and comfort of indoor living and the harsh reality of life in the garden that helps to acclimate your seedlings before the shock of transplanting. Plop your seedlings into the cold frame and -prop it open during the day for ventilation (otherwise you risk burning your plants). Close the cold frame at sunset to lock in the heat. This will keep temperatures moderated and protect plants from hard rains while exposing them to being outdoors. If there's a hard frost coming your way, throw a blanket on top of the closed cold frame to keep the heat in.

If you don't have a cold frame, you could bring your plants outside on nice days and take them in every night. However, building one is fairly easy, and I would recommend it. I built mine with friends, a hand saw, a power drill (though I could have used a hammer), and some old windows I picked up from the side of the road, and a couple of old hinges and drawer pulls. We used old 2"X10" planks. The procedure is absurdly easy.

Build a cold frame
Cold frames are a really great home building project, especially given how much people will charge for a pre-fab one. I would definitely recommend building your own. Start out by studying what you're building so that you understand the concept. If you've built anything before, the basics of this project will be fairly obvious. If you haven't, you might want to consult instructions in this book or on the web. The type of cold frame I outline below is like this one, but made with only one row of panels in the front and two in back. While building, keep in mind that cold frames are sloped, facing south, so as to maximize the amount of sole exposure and minimize shading. Also keep in mind that any part of your coldframe that isn't flush or properly fitted will let out precious heat on cold nights.

Materials
- Salvaged window, glass door, shower door, or frame with plastic. Storm windows are best, but not necessary.
- Salvaged 2x8 - 2x14 boards (just make sure they're not pressure-treated)
- Scrap wood (preferably 2" square) for bracing, 2 cut to the width of a single board (8-14"), 3 cut a hair shorter than double that length, and 2 cut to a middle length (doesn't have to be exact)
- Screws and drill or hammer and nails
- 2-3 hinges and screws
- A Drawer-pull
- Hand saw, chop saw, circular saw, whatever.
- a chisel
- Shims, Weather stripping, and/or caulk (if you need it)

The procedure
- The first part of any building project is the math. First measure (twice!) the length and width of your window and write this down. Your longer front and back panels will be the exact size of the length of your windows. Mark this length for 3 boards, keeping in mind that the saw will turn a few millimeters of solid wood into dust. That 1 board for the front and 2 for the back.

- Next, measure the width of your windows (twice). Write this down and then measure the height of your boards, which should be just shy of 2 inches (and jot it down). The shorter panels for the sides of your cold frame will fit inside the long panels, and therefore need to be measured to the width of your window minus 2 times the height of the boards. Therefore, if your window is 28" wide and your boards are 1.75" high, your boards should be cut to 28-(2*1.75), or 24.5".
Again, mark out and measure 3 boards of this length. That's 1 for either side plus a third that will make the slope on both sides.

- Now that you've measured and marked everything twice, cut your panels - 3 long ones, 3 short ones.

- Now comes the Hard part. Draw a diagonal line that bisects one of your short, side boards and forms two long triangles. Take into account the width of the saw to make sure that, when cut, the triangles will be identical. These two triangles will form the slope of your cold frame. Take a deep breath and cut the board on the diagonal, so that you have two triangles.

- Phew! Now let's assemble. You're basically building a sloped box in two teirs. Use 4 of your pre-cut bracing wood on the interior 4 corners (the two short ones in front and 2 of the longest ones in back, making sure the long ones are flush with the bottom of the boards and stick up in the air). Attach the bottom four pieces by screwing/nailing the boards into the 4 corner braces - remember, the sides fit inside the front and back boards.

- Next, Add bracing wood to the middle interior of each side except the front so that everything on the bottom is flush. The 3rd long piece should be in the center of the back sticking up and the two middle-length ones should be halfway along the sides sticking up (make sure they're in a place where they won't stick up over the sloping side panels). Add the top boards on the sides and back of the cold frame by drilling or screwing them into the bracing wood. You can add toeholds into the bottom boards, but this isn't necessary. Make sure everything is tight and together. Lift the frame to make sure it's sturdy.

- Now that you have the frame done, set your window on top and make sure everything fits. Make sure the window sits flush and tight against the top of the box. Attach the window to the frame by attaching hinges to the top of the cold frame and the window - making sure to keep it it as flush as possible. It wouldn't hurt to chisel out a small depression in which to set the hinge to prevent the window from lifting off of the back by the width of the hinge. If you don't have a chisel handy, you'll probably end up having to add weather stripping to the back seam. If you've never attached a hinge before, make sure you have someone there who knows how to do it or else really spend some time with that hinge to figure out the right side, the wrong side, and how it wants to be attached. Hinges are trickier than they appear. Once attached, lift the door to make sure they're on properly.

- Finally, attach the drawer pull to the center front of the window so that you can lift it easily.

- Check for any holes and add weather stripping or caulk where needed. If you want, paint it with a light, nontoxic paint to help it weather better and to reflect light back onto the plants.

Congratulations! You have a cold frame!