January 24 marks the day we reach 10 hours of daylight, which means gardeners can look forward to favorable conditions for vegetative growth. Longer days and gradually rising temperatures make this the perfect time to kickstart your gardening season. But with limited south-facing windowsill space, consider building cold frames and other DIY solutions to start growing crops outdoors this month.

Cold frames are simple, cost-effective gardening structures that extend the growing season by protecting plants from cold weather. Acting like mini-greenhouses, they trap solar heat and retain moisture, allowing seeds to germinate and plants to grow even in chilly conditions. Best of all, they’re easy to build using recycled materials, often available from your local Habitat for Humanity ReStore.

When purchasing seeds, it’s best to focus on cold season crops that can withstand freezing temperatures. Kale, chard, Asian greens, lettuces, radishes, spinach, beets, turnips, mustard greens and kohlrabi do well, provided they have some help getting started. Most cold-season crops germinate at soil temperatures of 40-60°F. Lettuce and spinach can germinate in the mid-30s, though it takes longer. At 50°F, the success rate improves dramatically.

A straw bale cold frame creates a small greenhouse to warm the soil and protect young seedlings from overnight cold.

DIY SOLUTIONS FOR YOUR WINTER GARDEN

• DIY Cloches
In Europe, glass bell jars (cloches) warm the soil to encourage early germination. You can replicate this by cutting the bottom off a plastic gallon milk jug, sinking the top into the soil by 1-2 inches and removing the cap during the day to let in moisture and prevent overheating.

• Straw Bale Cold Frames
Create a simple cold frame with six straw bales and a glass door. In the garden, arrange two bales lengthwise on each long side of a rectangle and one bale at each short end. Place the glass or a framed plastic panel on top to trap heat. This setup creates a small greenhouse to warm the soil and protect young seedlings from overnight cold. By March, as crops mature, you can dismantle and relocate the frame to start another batch of crops early.

• Solarize with Plastic for Large Gardens
For larger spaces, use 6-millimeter clear plastic to solarize garden beds. Dig a 4-inch-deep trench around the perimeter, tuck the plastic edges into the trenches and cover them with soil to seal in heat. Prepare crop beds and add nutrients before solarizing to avoid disturbing the warmed soil later. If you leave the plastic in place after weed seeds sprout, they’ll bake under the heat, leaving you with weed-free, warm soil ready for planting.

• Traditional Cold Frames
Build a more permanent cold frame with scrap lumber and a hinged glass or plastic lid. These structures can be propped open during the day for ventilation and are often positioned against a house or outbuilding for additional thermal gain.

Sizes vary based on the availability of materials. To maximize growing space and solar gain, use a 4-by-8-foot frame and create a sloped top by building the south wall 12 inches high and the north wall 18 inches high. If you’re using plastic instead of glass, secure the edges with wood lathe and screws for a tight, durable seal. Avoid staples, as they can leave gaps that allow air and moisture to seep in.

If building your own cold frame, paint the north interior wall black to absorb more heat, and use seed-starting heat mats with thermostats to maintain optimal temperatures while conserving electricity when not in use.