Row Covers

Quick Facts

• Row covers provide both frost protection and a form of mechanical control within integrated pest management.
• Row covers are generally made of spunbond or netted synthetic materials, such as polyethylene, polyester, or polypropylene.
• Support row covers by hoop structures or by laying directly over the tops of crops needing protection.
• For effectiveness, coordinate applying row covers with the targeted pest’s life cycle and the growth stage of the crop.

In agricultural use, a row cover is a transparent or semitransparent material that is used over crops (typically vegetables) for a variety of purposes (Fig. 1). As an integrated pest management tool, row covers act as a physical barrier that prevents the movement of pests such as insects (Table 2), birds, and mammals, to host plants. This form of management is popular in organic production to avoid chemical application. Row covers are also used to shield crops from environmental factors like cold or hot temperatures (Table 1), and wind. Commonly used methods of application include floating row covers, hoop-supported row covers (also called low tunnels), and plastic-covered trenches.

Materials

Row covers are generally made of polyester, polypropylene, or polyethylene (poly). Polyethylene may be clear or pigmented and either stretched across a trench or supported by hoops (Fig. 2). Row covers may be vented or unvented. Lightweight materials are effective as an insect barrier starting in late spring. Other fabrics that are heavier in weight are used to extend the growing season by protecting the crop from early or late frosts. All materials are fabric-like and generally spunbonded or nonwoven (Fig. 2). Both may be left to lay on the surface of the soil or can be supported by wire hoops (Fig. 3). A few common brands of the spunbond fabrics include Agribon® and Reemay®. Lightweight row covers tend to rip easily, and thus, have a short life span (up to a few months).

Woven materials include thicker fabric or a plastic mesh. For example, the Proteknet brand of mesh is available in six grades ranging in sizes from 0.85 mm2 to 0.85 mm x 1.4 mm. Select the mesh grade to ensure the target pest cannot pass through the material.

Plastic-covered trenches allow for early seeding and plant growth and provide some frost protection (Fig. 5). Polyethylene is generally stretched across a trench about 7 inches deep. Use a mechanical mulch layer attachment to lay the plastic and mound the soil along the edges of the bed to keep the plastic in place.

Row covers may be purchased online through garden supply and seed companies or at some selected garden centers. When selecting the support structure for row covers, consider whether it will be used for a single season or multiple uses. Options include 3/4-inch bendable PVC, metal hoops, or small wire hoops (Fig. 3).

Table 1. Row Covers Vary in Weight, Light Transmission, and Heat Retention

Characteristics	Lightweight material	Mediumweightt material	Heavyweight material
Weight	0.45 oz/yd2	0.50 – 0.55 oz/yd2	0.90 – 2.0 oz/yd2
Light transmission	90%	85%	30% – 50%
Frost protection	---	28°F	24°F – 28°F

Table 2. Insects Excluded From Various Insect Netting Mesh Opening Sizes

(Table adapted from Proteknet Insect Netting brochure)

Species	0.0138 in.² (0.35 mm²)	0.0335 in.² (0.85 mm²)	0.05 in. X 0.07 in. (1.2 mm X 1.9 mm)	0.19 in. X 0.12 in. (5 mm X 3 mm)
Aphids	X
Flea Beetles	X
Lacewings	X	X	X
Ladybugs	X	X	X
Leafhopper	X	X
Lygus bugs	X	X	X
Moths	X	X	X	X
Root maggot flies	X	X	X
Stink bugs	X	X	X	X
Spider mites	X
Squash bugs	X	X	X	X
Thrips	X
Whitefly	X

Construction

When constructing row covers, first decide which crops to cover. Then, identify the purpose of the cover. For insect exclusion, be aware that timing is important. Understand when the pests can be most destructive to the crops and plan to leave the covers up for that duration of time. Also consider crop growth timing and size for the height of the row cover (Table 3).

Next, decide the length and width of row cover you will need. Remember, you will need enough row cover to reach and cover both ends of the row. The structure can be built over existing beds and rows with plastic mulch and drip line. First, install the PVC, metal, or wire hoops, then lay the cover over the frame and secure with binder clips (Fig. 6). Completely cover the crop on all sides. Cut row covers easily to size using scissors. Allow extra room for crop growth.

Finally, secure the row cover edges with soil, rocks, or other heavy objects (Fig. 7). Shovel soil or place large rocks every 3 feet or so along each side of the row cover to exclude insect pests and to keep the wind from lifting the cover. Landscape staples are available to help secure row covers along the edges; however, they have the potential to tear the row cover.

Pest Prevention

To effectively protect crops from insect pests, lay the row cover over the plants before pests are evident in the area (Fig. 8). It is critical to protect seedlings in early spring when most adult pests become active and again in late July and early August. Inspect seedlings prior to transplanting to ensure there are no insects in the soil or on the transplants. Also, rotate crops by family to avoid laying row covers over plants where eggs may have been laid the previous year. Regularly check under the row cover for pest problems. If pests are found, treat infested plants with an approved insecticide, or remove and discard the infested plant material.

Maintenance

Weeds grow quickly under row covers; therefore, weed barriers may be helpful. Another option is to occasionally pull back covers to hoe and hand-pull weeds. If not using drip irrigation, lift the row covers to allow watering. Deer and other animals can damage row covers, so it may be necessary to set up fences to keep them away from covered plants. Clean row covers may last longer since soil particles can abrade and tear these covers. Row covers can be hosed down with water to clean, but it is important to let them dry completely. Store row covers indoors in plastic bags or containers. Mice may nest in row covers if left in sheds, barns, or garages.

Constructing an A-Frame Row Cover

(Instructions from University of Maryland Extension)
For a raised bed: 3 feet wide x 8 feet long x 4 feet high

1. Drive a 6-foot metal fence post 2 feet into the ground at either end of the raised bed and connect the posts with a piece of wire.
2. Fasten pieces of wire from the top of each post to the corners of the raised bed to create the “A” and provide support for the row cover.
3. Cut a 12-foot x 10-foot piece of row cover and drape it over the top wire and pull the excess fabric around to close off the ends.
4. The top of the wire is 4 feet from the ground so you can drive plant support stakes next to each plant directly below the row cover. Secure the row cover with sod pins or boards.
5. Alter dimensions and construction techniques to accommodate specific situations. Cut costs by reusing and recycling materials around your home. The useful life of PVC pipe and rebar is at least 10 years.
6. Build a reusable frame from wood, PVC pipe, #9 wire, or other available materials to support floating row covers. This works well for single rows of tomato, pepper, and eggplant. Example: a 6-foot-wide roll can cover a 3-foot-wide plant bed, while providing enough room for seedlings to grow upright.