Extend your garden’s growing season by protecting plants against early frosts.
At Cleveland Botanical Garden’s Learning Garden, row covers are used directly over newly seeded areas to warm air and soil, prevent moisture loss due to drying winds, and keep animals and pests from taking the seeds.
Row covers are made of a breathable material that transmits air and water through it.
Gardeners can’t outrun Mother Nature. She determines when we stop or start our gardening season, but with a few tricks, we can stay ahead of her for as long as possible. Row covers are one way. Include them in your gardeners’ bag of tricks to wring extra weeks and months out of your growing season.
Row covers are terrific multi-tasking tools that extend growing and harvesting time by protecting plants from frost and drying winds and minimizing transplant shock. In areas with milder winters, using row covers over cold-hardy edibles extends harvesting into winter. Row covers are also extensively used for organic pest control. They form a barrier against insect pests and keep birds from stealing bramble crops. During the summer, row covers make good shade cloth for propagating cuttings.
Until row covers were developed, home and commercial gardeners used rolls of clear plastic over plant rows to create a greenhouse effect. This worked well to warm air and soil, but had drawbacks: plastic was unwieldy to work with, air couldn’t circulate (which led to fungal problems) and on warm days, it got too hot inside, which quickly dried out soil and baked plants. Impermeable to water, the covers had to be removed to water plants or drip irrigation had to be used.
Admittedly trapping less warmth than plastic covers, the newer fabric row covers have important advantages over plastic. Today’s row covers are made from extremely lightweight, loosely spun polyester and polypropylene, which make a material that, like plastic, transmits sunlight, but unlike plastic, is a breathable material that transmits air and water through it. Depending on the thickness, row covers allow from 60 to 90 percent light transmission and provide frost protection to about 24°F. They can increase ambient temperatures by 10°F.
Because the covers are so lightweight, they can be placed directly on plants. With just the edges secured with rocks, stakes, or soil, as plants grow, they naturally push or float up the covers, eliminating the need for wire hoops. (They are also known as floating row covers.) While they can be placed directly over plants, especially low-growers such as thyme, prostrate rosemary, dwarf lavenders, and even strawberries, I prefer to use them over wire hoops because under windy or heavy rain conditions, covers draped on plants such as basil can cause stem breakage.
For smaller gardens or rows, simply cut the fabric to fit the row size. Instead of using wire hoops, stake the fabric up using durable metal or wooden stakes. For sturdy herbs, such as rosemary and lavender, simply drape the fabric over the top of the plant. I have a rectangular bed of perennial herbs in my backyard—about 4 feet by 10 feet—for which I do this each fall. I cut a piece of row fabric and place it right over my rosemary and lavender plants. If using hoops, be sure to secure the fabric on top with clothespins because strong winds can blow them away if they’re not properly secured.
Wire hoops made for row covers are sold at most garden centers and in garden supply catalogs or can be made using coat hangers or other sturdy wire. For gardeners who would like to be able to walk inside the row covers to weed, harvest, water, or thin plants, larger hoop frames offering up to 6 feet of headroom are available.
Covers let in light and water yet keep pests from damaging plants.
Row covers are sold in rolls. Standard sizes are usually 6- or 12-feet wide with lengths of 20- to 100-feet long. They can also be purchased in square or blanket sizes to drape over plants not planted in rows or to cut to size. Covers are affordably priced at around $10 for a 6-by-30-foot roll and about $30 for a 35-by-35-foot roll. Covers have UV light protection, making them reusable for several years. However, some gardeners find that they only get one season of use from the lightest-weight fabrics.
Reemay is the best-known commercial brand of row covers because it was one of the first available. Others include Typar, Agribon, Agro-Fabric, and Covertan.
The lightest row covers weigh less than 1/2 ounce per square yard. The most lightweight covers are best used for summer insect protection rather than spring or fall frost protection. If using for pest protection, cover plants before a pest emerges. Consult your local extension agency for specific emergence information on pests in your growing area.
Mark Langan, a commercial herb grower and owner of Mulberry Creek Farm in Huron, Ohio, has been using row covers for years. He uses lightweight covers to keep Japanese beetles off of his basil plantings. “I apply them before the beetles emerge in early July,” Langan says. “The covers let in light and water yet keep the beetles from damaging the plants. They’re also great for keeping cucumber beetles off my sage plants in early summer.” Langan also uses the covers in the fall to wring extra weeks out of tender herbs such as basil, pineapple sage, Mexican sage, and other tender salvias. By protecting his sage plants in the fall, he says, “We can harvest fresh sage leaves that are the best for making our Thanksgiving stuffing.”
If you’re using row covers for frost protection, look for heavier weights of 1 to 2 ounces per square yard. While the heavier covers offer better cold protection, they emit less light. So, when selecting a cover, consider the average low temperatures in your area and how much protection you need.
For example, if you want to extend the growing season of parsley, lettuce, or basil in the fall when a light frost may occur, a mid-weight cover that offers several degrees of frost protection while allowing adequate light in during the day will work fine. To extend the season into late fall or early winter when heavier frosts occur, use a heavier-weight cover; but because the heavier weight emits less light, remember to pull it off of plants during the day so the plants receive enough light to grow. In areas where lavender, rosemary, and other plants are marginally hardy, drape row covers over those plants in late fall to help successfully over-winter them.
Experiment to find the best use of row covers in your own growing area.
In early spring, install row covers several weeks before the last average frost date for early transplanting of cold-hardy seedlings. Especially useful to apply over newly seeded areas or rows of plants, they prevent birds from eating seeds and protect against drying winds that increase soil evaporation and can leave a crust on the soil surface. If using heavier-weight covers in the spring or fall, and temperatures reach high and humid ranges, the covers may need to be vented—by rolling up the sides—so that heat and moisture buildup do not cause disease problems.
It takes experimentation to find the right formula for the best use of row covers in your own growing area. And a tip for those without the desire (or energy) at the end of the season to spar with Mother Nature—row cover fabric is great for making ghosts for Halloween.
Maureen Heffernan is the director of public programs at Cleveland Botanical Gardens. She is also a freelance writer and herb lover who lives and gardens in Cleveland Heights, Ohio.
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