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A handy friend gives Sharon advice on how to build a cold frame.

Friday Feb 08, 2008.     By Sharon Hoyer

Lifestyle Feed

As difficult as it is to believe during February (a.k.a. the most dismal month of the year), spring is coming. Really, it is. And right about now, those of us with gardens can feel our green thumbs starting to itch. I'm currently hatching a scheme to install a backyard grape arbor and my first potted roof garden. My mom confessed she's already peeking beneath snow piles and sodden mulch on a hunt for the first crocus of spring. Sadly, it's not time to chase the spiders off our hand trowels just yet, but, for those unwilling to accept Punxsutawney Phil's forecast, use of a cold frame can bump up the growing season a month or more.

A cold frame is essentially a miniature portable greenhouse, consisting of low walls made from wood, brick or straw bales, with a glass or clear plastic lid. Cold frames are most often used to toughen up seedlings that were started indoors, providing a gentler transition between the cozy windowsill and the big, bad yard. You can place the frame directly over a portion of the newly-planted bed you wish to insulate, and remove it when the plants become hardier. My mom uses one on her back patio to shelter flats of herbs and young annual flowers before planting.

I've always wanted to build a cold frame of my own to nurture edibles in the pre-spring, but never found the time (or requisite drafting skills) to put one together. Enter my friend Joe—as handy with a plane as he is with a pruning knife—who used his hibernating months to construct a handsome cold frame from salvaged materials. I stopped by his place the other day to learn how he did it.

The frame he built measures roughly five-feet by three-feet. The glass lid slopes down in the front to catch as much sun as possible, and the interior is painted white to reflect that sun onto the plants inside. An adroit carpenter and dedicated DIYer, Joe calculated the dimensions to most efficiently use the materials he had on hand. He procured some cedar planks that were leftover from a fence his dad built, and found an old window frame in storage under his back steps.

After admiring his craftsmanship, I sat down on the couch to learn about the drafting process. Using the dimensions of the window and the amount of slant he wanted for the top as base figures, he deployed the Pythagorean Theorem and some basic trig to calculate the lengths and angles at which to cut the planks for the sides. If, like me, you feel the room spin at the mention of sine, an easy-to-follow cold frame plan can be found here.

The actual construction didn't require too many tools: a chop saw, circular saw, drill, square and wood screws. A few final touches were still needed: weatherproofing the frame and attaching hinges to the lid, an essential step since cold frames should be ventilated every day. Overheating is often a bigger problem than excessive cold—so much so that temperature-activated cold frame openers can be commonly found at garden stores.

As you can see, the near-final product is a real beaut. Joe plans to use it for young herbs and tomato plants starting in March and cold-weather greens, like kale or chard, in the late fall. I'm inspired to roll up my sleeves and get to work on one. That is, as soon as I can wade through the slush to my garage.

Thinking about doing some cold framing of your own? Here are a few ways to get the most out of your little greenhouse:

1. Angle it toward the south or east to catch as many rays as possible throughout the day.
2. If you're putting the frame over a garden bed, bury the sides about six inches and build up the soil around the outside. More heat will be trapped in the earth beneath the frame.
3. Be sure to lift the lid at the height of the day. Temperatures inside shouldn't exceed 75 degrees Fahrenheit. You might even want to invest in a thermometer.
4. On cold nights, add extra insulation by covering the frame in newspaper, straw or blankets. During really cold nights, you can even place a votive candle or two (about one candle for every two square-feet) inside to keep things cozy. Just be sure to keep the flame well away from the sides (don't do this if you're using straw bales for walls!) and any leaves that might burn or catch fire.
5. Irrigate with warm water; cold water can be shocking for young plants. Also, avoid over-watering so your seedlings don't succumb to rot or disease.

It took a move from the regimented lawnscapes of the suburbs to the congestion of a major metropolis for Sharon to look twice at what she puts in the trash, down the sink and into her own body. She reports fortnightly on her endeavors to change "greening" from calculated deviation to a practicable way of life. You can contact her here.