Keep Your Garden Growing Through the Winter

Cold frames, hot beds, plastic-covered tunnels, cloches, and even such mundane household items as cardboard boxes and old blankets can help the home gardener stretch the growing season for weeks or even months to maintain a productive garden with certain cold-hardy crops, hardy flowering annuals and short-lived perennials.

Cold Frames

Cold frames are one of the best ways to keep plants growing through the winter. It’s basically a box with a translucent top to let in the light and collect solar warmth. You can make a low-cost cold frame using wood, concrete blocks or even bales of hay for the box. Old storm windows are typically used to create the top, but you can also use sheets of corrugated fiberglass or heavyweight clear plastic.

The first thing to consider before building your cold frame is location, location, location! It needs to be in full sun to create enough warmth for the plants sheltering inside. A south-facing wall works best. Against a heated house is ideal, since this adds extra warmth, but a garage, other outbuilding or even a solid fence will suffice to provide a degree of shelter against winter winds and weather.

The location must also have good drainage. A site that slopes slightly downward is best, or you can build it up to create a slope. The cold frame should be set a few inches down into the soil.

You can find plans for building your own cold frame online. It should have a way to prop the cover open to vent it on warm, sunny days to keep your plants from cooking in the solar heat, or to allow you to weed or harvest. It’s a good idea to weight or latch the top down so that it doesn’t blow off in high winds. During periods of extended freezing-cold weather, an old blanket draped over the cold frame at night can make all the difference, providing you remember to remove it during daylight hours.

The dimensions shouldn’t be more than 3 or 4 feet deep for your comfort. The simplest type of cold frame would be concrete blocks or bales of hay with a sheet of clear plastic laid on top. If you make the frame with wood, use a type of wood that won’t rot easily, like cypress or cedar.

Food crops that can be grown during winter in a cold frame include:

• Arugula
• Broccoli
• Beets
• Cabbage
• Chard
• Chinese cabbage
• Green onion
• Kale
• Lettuce
• Mustard
• Radish
• Spinach

Hardy annuals like pansies and dianthus, and short-lived perennials propagated from stem or root cuttings such as sweet Williams, Shasta daisies and hollyhocks, need a little winter sunshine and do well in cold frames. Bulbs being forced into bloom are also candidates for a cold frame.

Cold frames are also good for getting an early jump on the gardening season in the spring for cold-hardy crops, or for hardening off seedlings just prior to planting.

Hot Beds

Hot beds use the heat of decomposition to keep garden beds warm over the winter. To make a hot bed inside a cold frame, dig a hole at least 12 inches deep and fill it with fresh horse manure mixed with straw, and topped with 6 inches of soil. As the manure decomposes, it releases heat into the frame.

This technique can also be used in your outside garden beds for broccoli, spinach or other crops that need abundant nutrients. According to Mother Earth News, if you dig out a bed and refill it halfway with compost, mixed with the cheapest dry dog food you can find to activate the decomposition process, and then top it with 6 inches of soil, the compost will generate enough heat to keep the little plants from freezing. In the spring, when the plants’ roots grow deep enough to reach this rich mixture, they’ll take off like gangbusters.

Plastic Tunnels and Cloches

Plastic tunnels are used to protect larger cold-hardy crops, starting in early winter. These are relatively easy to make yourself, and the instructions can be found online. Face the tunnels into the prevailing winds to minimize stress on the tunnel walls. Plastic tunnels also lend themselves to early spring plantings, to warm the soil and protect from insect pests while plants are young and tender.

Cloches are small covers set over individual plants. You can buy them through garden supply catalogs or make your own out of plastic milk jugs by cutting off the bottoms and leaving the top uncapped for ventilation. Small beds of pansies, snapdragons or annual dianthus may sail through the winter if protected with cloches, and then bloom very early in the spring. Keep them anchored with a deep mulch, which also provides extra insulation.

This technique also works in the spring for hardy vegetable seedlings like cabbage, broccoli and parsley to ensure survival during late spring freezes.

Blankets and Boxes

Using old blankets, sturdy boxes or bushel baskets to insulate hardy plants from frigid winds or ice is especially effective in Zones 6 and 7, where winter seems to come and go. When a winter storm is predicted, cover young roses, fall-planted perennials or hardy vegetables until the stressful weather has passed.

For more information on how to keep your winter garden protected and productive, please read Protect and Maintain Plants in a Cold Climate.