Down the Garden Path: Guest columnist series –Cold frame gardening gives an early start to the season

Editor’s note: As of April 29, 2022, Richard Hentschel has retired from University of Illinois Extension with nearly 30 years of service as a Horticulture Specialist and Educator in northern Illinois. As this growing season begins, a selection of qualified Extension guest columnists will occupy this space. In time, another Extension Educator will join our communities and likely continue this column, a long-standing Kendall County tradition.

Nature’s timetable for when we can plant rarely aligns with my own need to get out in the garden and plant. Yes, as gardeners we are accustomed to our hopes being dashed by Mother Nature, but human ingenuity has developed ways to carry on. The ultimate solution is having a greenhouse, but for most of us the expense and size limits our ability to have this luxury. Fortunately, the greenhouse’s much smaller cousin, the cold frame, can fill the need.

A cold frame is essentially a low box with a clear top that acts exactly like a greenhouse. It can be placed directly in the garden or filled with pots on a patio. Some can be permanent, others, like mine, are portable, and can be knocked down and easily stored during summer. While they can be purchased complete, most often they are homemade, using salvaged window sashes or storm windows. Plans are readily available on the internet.

The design is low-tech, but effective. When closed, the windows trap the heat of the sun, keeping the inside of the box warm during nighttime, with heat radiating from the soil. While cold frames should be built to retain heat and block the wind, they also need to be opened when sunny days with warmer temperatures occur during early spring. On such days, temperatures inside can exceed 80°, so most cold frames have lids that can be propped open or removed.

The versatility of the cold frame makes it invaluable as a tool to extend the growing season. Last fall, I placed it over a row of swiss chard, and was able to harvest into January. This year, I set it up in the garden in February. When we finally had a few warmer days in March, the soil warmed enough to start radishes and lettuce for an early spring crop. Since the cold frame I use is portable, it could then be carried to another part of the garden where I could use it to get an early start hardening off tender plants such as tomatoes.

A cold frame built now will provide years of early- and late-season gardening satisfaction – a priceless investment in future garden happiness. I built mine 10 years ago and it has continued to help me get my hands in the soil long before the weather would normally allow it.

Have questions for the University of Illinois Extension Master Gardeners? You can call, email, or visit during the growing season. Learn more about connecting with the Kendall County Master Gardener Help Desk at go.illinois.edu/HelpDeskMGdkk, or call or visit during office hours: Monday, Wednesday, and Fridays from 9 a.m. to 12:30 p.m. at 630-553-5823 or at 7775-B IL Route 47, Yorkville.