The Benefits of Using Row Covers in the Garden

To Exclude Insect Pests

Certain fabrics make excellent barriers for organic insect control. Some are marketed specifically as insect barriers, whereas others are simply lightweight row covers. They can be used for a variety of garden pests; I’ve had particular success with them in the ongoing battle against cabbage worms on my broccoli.

An insect cover works in several ways. First, it creates a physical barrier that pests cannot penetrate. Second, the cover hides the plants from sight, keeping many insects from finding their target. Usually insect barriers are laid directly on top of the target plants, but some gardeners prefer to use hoops to support the fabric. Because these fabrics are virtually weightless, this additional measure isn’t strictly necessarily, but many gardeners find the sight of tidy tunnels over the crops to be pleasing.

However you choose to install your insect barrier, the most important consideration for this organic insect control is timing. The cover needs to be in place long before insects become a problem. If installed too late, you might simply be trapping the offending insects under the fabric. They’ll be protected from the birds and predatory insects that might normally eat them and instead spend their days leisurely enjoying their favorite food — your veggies.

Typically, an insect barrier is laid on the garden as soon as the bed is planted or seeded. The edges of the cover must be buried well to prevent pests from crawling under the fabric. Keep in mind that if you’re trying to outwit an insect that overwinters and emerges directly from the soil, you’ll need to combine a cover with a yearly crop-rotation plan. Even a small garden will benefit from an annual shifting of crops.

Once your row cover is in place, don’t forget to take an occasional peek beneath the material to ensure that no pests have infiltrated your defenses. Knowing the life cycles of some common garden pests is also a good idea.

Also remember that many plants need to be pollinated in order to produce a crop. Therefore, it’s vital that you remove the insect barrier when these plants begin to bloom. Some plants that must be pollinated are cucumbers, squash, peppers, tomatoes, and melons. Certain crops, such as broccoli and cauliflower, don’t require pollination and can be left under their cover until they’re ready to be harvested.

To Protect Seeds and Seedlings

You can also use row covers to speed up seed germination and protect newly planted seeds and seedlings from a variety of pests. When you plant seeds in a garden bed, you must ensure that the soil stays relatively moist until the seeds germinate. In my area, the frequent spring rains are a big help, but when a dry spell strikes, a light- or medium-weight row cover can come to the rescue. When installed over a newly planted and watered bed, the cover will trap some of that moisture, as well as retain heat, helping seeds germinate quicker.

Row covers will also help protect against heavy rains, which can cause soil crusting. Crusty soil makes it difficult for small seeds to poke through, leading to spotty germination among certain crops — notably carrots and parsnips.

Covers also protect against birds. At times I’ve come inside after planting seeds only to look out through the window and see a large flock of birds feasting on the smorgasbord I’ve provided. I’ve also had birds nip off the tops of my young bean plants, leaving just sad-looking stubs in the soil. In times like these, I remember that securing a row cover would have taken only a minute or two.

To Warm the Soil and Protect Against Frost

Extending the garden by several weeks in both the spring and the fall is easy with a light- or medium-weight row cover. In spring, cool-weather crops such as radishes, spinach, arugula, lettuces, peas, carrots, and beets, can be started directly in the garden a few weeks earlier than usual if they’re covered with a light- or medium-weight cover. The cover will trap daytime heat, warming the soil and protecting the vegetables from frosty evenings. If you are using a medium-weight cover, remove it on mild days to expose your plants to maximum sunlight.

Even if no frost is imminent, you can still float a row cover over tender vegetables as a temporary shield. Not only will this save you the trouble of running outside in your robe and bunny slippers when you discover a late frost is likely (it seems that I always hear about an unexpected frost after I’ve hung up my gardening gloves for the night), but it will also trap some of the daytime heat, creating a microclimate and keeping your heat-loving vegetables a bit more toasty.

If you are covering tomatoes, peppers, or eggplants, make sure that the fabric doesn’t rest directly on top of the growing tips of the plants, as the abrasive rubbing of the fabric against their foliage can injure the delicate tissues. Instead, drape the fabric over tomato cages, hoops, stakes, or other supports. Once the risk of frost has passed, remove the coverings to allow air circulation and, eventually, pollination.

The soil holds a larger heat reservoir in the fall than in the spring, and you can use this to your advantage by covering up your tender vegetables when the cool weather threatens at the end of summer. A row cover will trap some of that heat, enabling you to protect your tomatoes and peppers while speeding up the ripening of any remaining fruits left on the plants.

Row covers can also be used in fall to provide late-season protection to cool- and cold-weather crops. Salad greens — arugula, spinach, winter lettuces, and mâche — along with late crops of carrots, radishes, baby beets, and leeks will appreciate the extra insulation of a medium-weight row cover on frosty nights.

For Ongoing Protection in Winter

For a year-round gardener, ongoing protection is perhaps the best use of row covers. Even if you’re not ready or able to invest in a winter cold frame or mini hoop tunnel, you can still enjoy a handful of homegrown winter vegetables all winter long with just a few minutes of work and a length of heavyweight row cover.

With a layer of organic material. In late fall, spread a 12-inch-thick layer of shredded leaves or seedless straw over winter vegetables (this method works especially well for carrots, parsnips, beets, celeriac, turnips, and leeks) and top it with a medium- or heavyweight row cover. When the craving for sweet garden carrots strikes in midwinter, all you have to do is pull back the cover and reach inside.

Over hoops. A heavy-grade row cover held on wire or PVC hoops can provide enough protection for certain hardy crops to be held in the garden, awaiting a cold-weather harvest. Some winter vegetables that can be grown this way are leeks, scallions, mâche, arugula, kale, collards, and spinach.

An extra layer. Use row covers to add an extra layer of protection to cold frames, mini hoop tunnels, and unheated greenhouses. This pairing of season extenders is key in creating a year-round vegetable garden that provides a nonstop harvest and requires no supplemental heating.

Types of Row Covers

Several sizes and grades (or weights) of row covers are available, and each has its place in a year-round vegetable garden.

Insect barriers. At the lightest end of the spectrum are the insect barriers. These virtually weightless, almost transparent fabrics allow up to 95 percent of light to pass through. They don’t offer much protection against a frost, but they may be left in place over crops for weeks at a time to prevent insect infestations. They work very well against a variety of insect pests, from cabbage worm to carrot rust fly to the cucumber beetle, as well as hungry birds and deer.

Lightweight covers. The next step up from the insect barriers, lightweight covers are a bit more substantial, weighing in at about half an ounce per square yard. Lightweight covers are also ideal for protecting newly seeded beds from birds and squirrels, or plants from insects, birds, rabbits, and deer. They will even boost seed germination by locking in heat and moisture. Most lightweight covers can provide up to 4°F (2°C) of frost protection and permit 85 percent of light to pass through to your plants.

Medium-weight covers. The medium-weight fabrics typically weigh from 0.9 to 1.25 ounces per square yard and are most often used for light frost protection or as a winter cover. Depending on the product, a medium-weight fabric will offer up to 6°F (3-4°C) of protection. It will also hold a bit more heat than the lighter-weight fabrics, but it may only allow 70 percent light transmission. For this reason, the medium-weight cover shouldn’t be used as an insect barrier during the growing season; there’s just not enough light to provide optimum plant growth during the spring and summer months.

Heavyweight row covers. The heaviest covers are often marketed as frost blankets and are used to protect crops from a heavy freeze. They typically weigh 1.5 to 2 ounces per square yard and can protect crops down to 24°F (-4°C). Because these covers offer only 30 to 50 percent light transmission, they are best used to shelter winter vegetables or as temporary frost blankets. If used in summer, they would block much of the light needed for healthy plant growth, as well as raise the ambient temperature around the crops. In winter, when there is less than 10 hours of daylight, the growth of most crops slows dramatically. Therefore, even though a heavyweight row cover prevents a good portion of the sunlight from reaching the crops, the goal in winter is protection, not growth.

Floating Row Covers and Supported Row Covers

Often, row covers are laid directly on the surface of the soil or on top of growing crops. Because they are so light, they “float” on top of the growing plants and are thus called floating row covers. But there are times when the cover should be held above the crops and supported on simple hoops: for example, when the cover needs to protect and insulate against heavy frost or winter cold, particularly for any length of time. If the cover is allowed to rest directly on top of the plants, the foliage may suffer cold damage.

Another factor that determines whether you should use a floating row cover or one with hoops is the weight of the fabric. The lightweight insect barriers and row covers are flimsy enough that they will not crush growing plants, but the medium- and heavy-grade materials that are often used in spring and fall as temporary frost covers may be too heavy for certain plants. In this case, a hoop support is beneficial.

Constructing temporary hoop supports. Hoop supports can be constructed out of PVC conduit, 9-gauge wire, concrete reinforcing mesh sheets, or anything else that can bend to a U-shape and has some strength. Place a hoop every 3 to 4 feet along the bed. I use 1/2-inch PVC pipes and insert each hoop end over a 1-foot length of rebar pounded into the ground for secure support. Alternatively, you can simply push the ends of the hoops 8 to 10 inches into the soil. If you’re working alone, it helps to temporarily use a few clamps or large clothespins to hold one end of the fabric in place while you stretch the other end over the hoops. Once you have the row cover on top, secure the fabric with a product like snap clamps, which lock the material to the PVC pipe. Also, be sure to secure the edges, weighing them down with rocks or sandbags or with a length of board or a small log laid along the sides. Whatever you choose should be easy to move aside, so that the cover can be lifted for easy harvest.

This excerpt has been reprinted with permission from The Year-Round Vegetable Gardener by Niki Jabbour, published by Storey Publishing, 2011. Buy this book from our store:The Year-Round Vegetable Gardener.