Bundle Up! Row Covers and More to Protect Your Garden Through Winter

Frost blankets and row covers offer protection from frost while still allowing sunlight to penetrate. GEA Stock/Shuttertock

As if shorter days and colder temperatures weren’t enough, putting the garden to bed until next spring can send one into instant Seasonal Affective Disorder. But what if there was a way to keep things growing? There’s a solution for every growing zone, from row covers, cold frames, affordable walk-in greenhouses, old sheets for those lucky enough to live far enough south, and more.

Let’s explore.

Frost Blankets

Frost occurs when moisture and humidity are just right to form tiny ice crystals on leaves, flowers, and vegetables. It typically occurs when temperatures are above freezing. In fact, the National Weather Service typically issues a frost advisory when temperatures of 33 to 36 degrees F are forecast. For areas with temperate winters and occasional frost warnings, old sheets, bedspreads, and even cardboard boxes will all provide varying degrees of protection. Make sure they don’t touch the plants, or they can act as a conduit to the cold. Never use plastic because most of it is too thin to make any real difference, it retains cold moisture, and it doesn’t allow the plants to breathe.

For longer-term protection, consider investing in a frost blanket, available in a variety of sizes and weights. Lightweight (1.5- to 2-ounce) frost blankets are suited for light frosts, offering protection of six to eight degrees above the daytime outside temperature and an average 40-percent transparency that allows sunlight to easily penetrate. A midweight (2.5-ounce) blanket offers 10 degrees of protection above the daytime outside temperature and 30 percent transparency to let in a good amount of light. A heavyweight blanket can offer protection of up to 15 degrees above the daytime outside temperature, but at 20 percent transparency, allows less light in.

Side note: Ignore “wind chill” or “feels like” readings. While human skin may notice the difference, it doesn’t affect plants.

Row Covers

A row cover, sometimes called a floating row cover when laid directly on the plants, is a spun-bonded or woven polyester or polypropylene material that looks and feels like gauze material from a fabric store. Relatively inexpensive, row covers also help with pest control. This is particularly important if a gardener is using them to get a jump on the spring season, as they help keep caterpillars, flea beetles, maggots, thrips, cabbage and tomato worms, maggots, leafhoppers, and other garden pests such as rabbits away from young seedlings. In fact, lightweight (0.45-ounce) covers are often sold as insect barriers, even though they offer two degrees of frost protection.

Because they are lightweight and allow 90 to 95 percent of the sun’s rays through, they can be left on crops such as salad greens, beets, and snap beans throughout the entire growing season until harvest. Medium-weight (0.5- to 1-ounce) covers offer four to six degrees of frost protection while allowing in a still impressive 70 to 85 percent of sunlight and are a top choice for early spring and late fall crops, as well as for overwintering. Heavy-weight material (1.5- to 2.2-ounce) covers offer eight degrees plus of frost protection, with 30 to 50 percent light transmission, and are a top choice for winter gardens. Most row covers are supported by specially-made wire frames or do-it-yourself frames made from PVC pipe, wood, or no. 9 wire and are recommended for use with medium- and heavy-weight cloth.

Cold Frames

Usually about 12 to 18 inches tall, cold frames are open on the bottom to the soil below and topped with a glass or plastic lid that provides access to the plants inside and lets sunlight in. While they are commonly made of wood, some gardeners use cement blocks or even bales of straw to create more insulated sides; an old window or glass door makes a convenient DIY lid. Another alternative is to make a wood frame with plastic stretched over it.

Some gardeners opt for stay-open hinges, but most use a wooden stick or piece of PVC pipe to hold them open on warm days, while other tops are just rested in place and easily removed. Manufactured cold frames and cold frame kits are readily available, ranging from moderately priced plastic models to more durable aluminum versions and up to large wood and glass masterpieces for luxury homes. The only limit is one’s budget.

Cold frames allow access to plants while still allowing light in. Paul Maguire/Shutterstock

A smaller option, often called a “cloche,” which is French for “bell,” is a large glass or plastic jar placed over an individual plant to act as a single plant cold frame. Raise the cloche by slipping a piece of scrap wood or large landscape rocks underneath the edge to vent it on warm days so the plants inside do not get too hot. While there are a wide variety of shapes and sizes available for purchase, a cloche can quite easily be made from an empty 2-liter soda bottle or large juice container, with the bonus that the cap can be removed on warm days to vent it. Winter gardening is all about thinking outside the box.

Year-Round Gardening

Large or small, made of glass and metal or plastic and polycarbonate sheeting, greenhouses were created to keep plants warm in the winter.

Solar and Thermal

The most cost-efficient way to heat a greenhouse is to use the sun’s rays. Dig the floor beneath the frost line. Then fill a large barrel with water and set it in a corner. The sun will heat water during the day, and it will disperse its thermal mass overnight.

Maximizing Warmth

The sun comes from the south in the winter months. Add extra insulation to the north wall to prevent heat loss, and paint the inside of it (which faces south) white to reflect the sun’s heat. For polycarbonate greenhouses, consider adding a second layer throughout.

Get Out the Power Cord

If the temperatures are going to stay below freezing, consider adding an electric space heater. It’s cost-effective, safe, and easy to set up. If it doesn’t break the bank, consider additional features such as a timer or, better yet, a built-in thermostat. It’s an investment that will last many seasons.