Cold frame

A sturdy cold frame can allow gardeners to continue to put freshly grown vegetables on their menus all winter long.

I’ve planted my winter garden and this season I’m a little more hopeful because my plants are now growing in a cold frame —which is a bottomless box with a hinged lid. A cold frame is a great way to extend our growing season and get more from your garden. Two features for success: its location and the lid.

The ideal location is a sunny southern exposure on a slight slope that allows for good drainage. Placing a cold frame in an eastern location may work if it is unobstructed by trees or other structures. A northern location typically does not get enough sunlight to grow plants and western locations can overheat in the afternoons.

Cool-weather vegetables such as cabbage, kale, spinach, beets, onions, and radishes will grow with as little as six hours of sunlight. The amount of light coming into your garden changes over the year. When trees lose their leaves, a shady location can turn into a sunny one, and the lower winter sun can shade an otherwise sunny spot.

The longer the exposure to the sun the warmer the growing environment inside your cold frame. Plants can continue to thrive even once outside temperatures dip below freezing. Encircling the sides of the cold frame with mulch, straw, or bubble wrap can help it retain heat over night. But it can also contribute to the cold frame overheating and that’s why you need a hinged lid.

Opening or closing the lid helps control the temperature of the growing environment. While hinges are available which expand or contract in response to temperature, a less expensive option is attaching a 18-24” stick to the frame’s exterior which can prop open the lid on warm days. Closing the lid in the late afternoon will help retain warmth over night.

While some gardeners recycle old windows for the lid, I’ve discovered the clear glass can allow too much sun to enter and overheat the growing environment. Old windows can also be heavy so I prefer lighter weight materials; but they have to be sturdy enough to hold up under accumulated snow in the winter.

I’ve used straw bales to form the frame and they work well enough. But as I get older I’ve found their extra width creates a barrier that I’m uncomfortable stretching over. Consequently, this year I decided to construct the frame from wood. The Extension Service recommends avoiding railroad ties and pressure treated lumber as the chemicals they contain can leach into the soil, something to avoid when growing plants for our dinner table.

This summer I bumped into a harsh reality. I’m handy, sort of. Because I drive a small car and lack the tools necessary to cut long boards, I couldn’t really build the frame from scratch. The good news is there are plenty of cold frame kits available.

Gardeners’ Supply offers one that suited my needs. I made their easy assembly process a bit longer by adding hardware cloth to the bottom of my frame. Having battled voles in the past I’m hoping this will keep them out of the perfect growing environment I created —time will tell if my plan is a good one.

Last year we were able to enjoy arugula and spinach all winter long. This year I’m trying out some new plants and looking forward to seeing what works. Experimenting in our gardens can be a year-round adventure.

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