Red Wicket Market Farm is a small farm 25 minutes from downtown Columbus, Ohio, near Slate Run Metropark. Breeding Black Copper and Blue Copper Marans to the Standard of Perfection.

Saturday, April 20, 2013

85 degree day? Let's build a cold frame!

Mike here today, writing to you about one of this week's projects. I'd been talking about the idea of cold frames for a few years, as one of the things on the very long "someday" list. With the flats of plants started in the basement already growing so well, getting one together became important. Nobody wants to shuffle plants back and forth twice a day to harden them off. Also, my mom was in town for a visit, and just mentioning a project like this to her means the power tools are coming out.

And you've heard what they say about Ohio weather. If you don't like it, wait five minutes. 85 degrees and sunny this week, but near freezing last night.

So, the tantalizing view of the finished project:

The construction is pretty simple, the sides are made of 5/4 x 6" ACA treated pine decking. The size is based on the size of the window sashes, so this one is 7' long by 38" wide, and stands about 11" tall at the front and 23" in the back. The original plan was to keep it very simple, but my mom insisted on the additional flat bit on the back, and since I constantly remind my kids to listen to their mother, I couldn't really argue the point in front of them. It did elevate this from "a crate with windows stuck on it" to something that actually looks designed, so yes, mom was right.
The windows came out of my house (but we did replace them first). I know Erika wrestles with my packrat tendencies, so projects like this that use junk to her benefit have to happen as often as possible.

The ideal top angle for a cold frame in this area has the windows pretty steep (for spring and fall, about a 40ยบ slope) But I worked out the angle based on the difference in height from front to back (two decking boards taller), how long the window sashes were, and a little help from Pythagoras. The front edge has a miter on it to match the angle of the sides.

The construction itself is very simple. Build the front and back flat on the ground, run some 2x2 braces to hold them all together--one on each end (inset by the width of the decking) and one down the middle. Then get an extra set of hands, some pipe clamps, or both, and put the ends on. The 1x4 you see above is added once the sides are in place, to hold the slanted sides because they don't reach the front. Everything is screwed together with treated deck screws. If you look closely, the screws are countersunk in the 2x2. That's only because I already had a box of screws that were a little too short that were leftover from a previous project.

Add a stout brace in the middle for extra support for the window sashes, and because you KNOW you're going to lean on it with your full weight when reaching the back corner.

Also, the decking board that I put on top carries the weight of the windows when they're opened. I tucked in some extra 2x4 pieces to create a big sturdy surface to screw that to.

The window sashes have this lip on them. Since my original plan was to mount the hinges on the TOP of the window sash, I forgot all about that design challenge. Then, I could either buzz that off or raise the hinges to compensate. It works.

This is also a good place to mention that dimensional lumber is nominal size, so a 2x6 is somewhere around 1.5" x 5.5" actual size, and any two boards can be different sizes. Plan to be flexible.
When picking a site for your cold frame, be sure to get a southern exposure, with some structure present to block prevailing winds (but be sure it doesn't shade the cold frame). For best results, always pick a spot with a big pile of rocks you have to move first.

(Why does that pile look so SMALL in this picture?)
Remove the sod and nestle the cold frame into the ground to keep wind from creeping in under the edges. If you have a site that drains well, you can even build it tall and sink it considerably into a hole (and add lots of brick or rock to the bottom for thermal mass). This site has the drainage of a baby pool, so it's dug in about two inches. Eventually, I'll add an inch or so of rock dust and fine limestone to the bottom to help with disease and pest management.

There is electricity in that barn wall, so this might become a hot frame someday.

Cold frames can get VERY hot on sunny days with little wind. Propping them open in the mornings is important. For hardening off plants, putting shade cloth over the top or painting on whitewash shading compound is needed. I'll be experimenting with whitewash recipes this week.

The cold frame will be ready for the tomatoes that are getting so big so fast.