Just to Come in from the Cold

Last year, it was quite discouraging to watch most of the plants I raised from seed slowly dying. (And for some of them, quickly dying.) Clearly, part of the problem was that several of my seedlings didn’t start out very strong – never mind dampening off, my seedlings were straight-up moldy. Adding to the problem, I planted my seeds straight into the cold, harsh ground from my warm, gentle house. Rather acclimatizing them to their new environment, like a climber getting used to a new altitude, I shocked them. This procedure did weed out all but the strongest plants – my tomato plant was a monster – but it would have been nice to keep a few more going. This year, I’m taking a couple of steps to improve my results. While I’m being more careful about my seeds not being contaminated, I’m also going to be more conscientious about hardening them off. So Chris and I recently built a cold frame.

Cold frames and their cousins, hotbeds, range from simple boxes covered with clear plastic to complex mini-greenhouses complete with digital thermometers and irrigation hoses. While cold frames don’t provide any additional heat to the plants in them, they trap sunlight during the day and insulate them at night. While it would be unlikely you could start seeds in a cold frame like ECO City farms does with their compost-fueled hotboxes, they’re perfect for creating an intermediate environment between the house and outdoors.

When considering our project, we decided we wanted to build a slightly complex box, with a glass lid but an overall square shape. Although most cold frames are a trapezoidal shape to catch the southerly sun – like this one described by Popular Mechanics – we decided that was too complicated. Instead of needing to build in grooves and cut funky angles, we decided we would just prop one side of it up with wood.

Having a plan, Chris and I went on a President’s Day shopping mission to gather the necessary supplies. First, we headed over to ReStore, a store run by the Montgomery County Habitat for Humanity that sells used housing goods. By purchasing from them, not only can you buy re-used construction supplies at hugely discounted prices, but you get to support Habitat’s mission to build houses for underprivileged families! In the past, I found a dining room chair that matches our other three almost perfectly for only $10. This time around, we were on the lookout for an old window. Although most windows included large sections of molding that would’ve gotten in the way, we finally found the perfect one – a simple pane of glass, surrounded by just enough wood to create a top. We also purchased two hinges and a snazzy black handle so that we could open the box easily. From there, we went over to Home Depot to pick up the right lumber. As our left-over lumber is inconsistent in size and the source of ReStore’s lumber is unclear, we wanted to buy it from the regular store. A lot of older lumber, especially things that are designed to be “weather-proof,” are pressure-treated with arsenic. So we bought a new 1 X 10, 10 foot long piece of non-pressure treated pine.

After we brought it home, I assumed we would work together to build the frame the next weekend. Much to my surprise on Wednesday, I received a text message photo from Chris showing a completed cold frame! After working overtime on Valentine’s Day week, he had the day off and was apparently bored. He said the hardest part was balancing the lumber on our work bench in the basement, as it was a little longer than anticipated and difficult to cut. We had it cut in half at Home Depot and from there, he cut it two more times to create four equal pieces. After that, he said nailing the lumber into an open-topped box was simple. From there, he screwed the hinges into the box on one side and into the window on the other side and added the handle. Unfortunately, he didn’t take any photos of the process. To weatherize it, we still need to paint it, which we plan on doing this weekend.

The completed cold frame, from the side. The top is a bit frosted over.

Although we haven’t put any plants in it yet, it would already be doing a great job if we had. It drastically increases the temperature during the day and even though it wouldn’t keep all of this warmth at night, it would keep the plants about 5 to 10 degrees warmer. In fact, it rose to more than 100 degrees on one sunny day! If we had been putting plants in there already, we would have opened the top up to keep them from frying.

The cold frame open. You can see our garden thermometer resting in there.

Now, I just need to keep my seedlings alive for long enough to put them in the frame…