Cold Frames ~ tis the time! How do cold frames work and how could you make a cold frame
Starting one’s own seedlings saves money an it’s an enjoyable practice that allows you to grow those special varieties you can’t always locate at your garden center. I built my cold frames using Hemlock; it weathers a beautiful grey and is very reasonably priced; .75 per board foot.
What is a cold frame?
It’s nothing more than 4 walls to trap heat and shelter plants with a transparent lid that admits light.
Choosing a site:
The best site is a south-facing, sunny spot with good drainage and protection from the wind. Ideally, the site should get full sun midmorning to midafternoon.
Cold frames store the sun’s heat while giving the gardener some control over temperatures with ventilation. In the spring the critical element in the cold frame is to keep nighttemperatures about 45℉ and daytime readings in the mid 70’s. Installing an inexpensive hardware store thermometer is a good idea.
You can grow cold frame plants in pots, flats, or, if you are growing just one type of plant (lettuce), plant right in the soil.
The key is paying attention to temperature- the trick is keeping it cool rather than warm. The way to keep the temperatures cool inside a cold frame is to lift the lid. A safe rule of thumb: when the outdoor temperatures are above 40 F, prop open the lid 6 inches; when he outdoor temperatures clear 50F, remove the lid. Be sure to restore the lid in late afternoon to trap the heat inside for the cool night.
On frigid nights, the plants inside the cold frame may need little extra protection to keep from freezing. Most heat escapes through the glass, so pile insulation on top. You can use old blankets, straw, or newspapers. Snow insulates well, too, but brush heavy snow off the glass so it doesn’t break.
Next, we'll give you a simple construction drawing so that you can build your own cold frame. Keep an eye out for discarded sash at flea markets, tag sales or your favorite "junk shop".