Row Covers: A Gardening Season-Extender With Benefits
As we enter the countdown to our first frost, many gardeners think about ways to extend the growing season to protect fall crops or to maintain hardy crops into and maybe through the winter. A quick investigation of options reveals myriad choices from DIY milk jug plant caps to water-filled plastic plant and row protectors to row covers, cold frames, hot beds and all manner of hoop houses and greenhouses. Each has a story of its own and may be the right solution for a given individual, depending on the gardening objective, budget, and level of commitment length. This article will focus on the benefits and construction of floating and hoop-supported row covers as simple, inexpensive and practical solutions that can extend both ends of the gardening season and provide some other in-season benefits as well.
Row Cover Basics
There are two common types of row covers in use today: floating row covers and hoop-supported row covers.
Floating row covers: Photo courtesy of University of Maryland Extension.
- Floating row covers use a spun bonded polyester fabric or plastic insect netting that is laid loosely but directly over the plants to be protected. The fabric can be held in place by anything with weight — from soil to bricks, stones, boards or pegs. Fabric covers offer as much as 4-5°F frost protection, although it is less for vegetation that is in direct contact with the fabric. This allows earlier planting in spring and extension of the fall harvest. Both fabric and netting provide insect protection. Coarser netting will keep out larger pests like caterpillars and moths. Finer nets exclude aphids, thrips and the like, which are vectors for diseases beyond the physical damage they do to plants. Floating covers are best used on relatively short crops, and they must be removed prior to flowering on fruiting crops that require pollination.
Hoop-supported row cover, also known as a low tunnel. Photo courtesy of University of Maryland Extension.
- Hoop-Supported Row Covers, also called low tunnels, sport some kind of hoop structure beneath a fabric or plastic cover. The tunnels provide more temperature protection than floating covers but are temporary and are conveniently removable, allowing flexibility for crop rotation, cover cropping and general soil building. Plastic covers come in various thicknesses. Thicker material is more rugged but reduces light transmission. Plastic can offer as much as 10°F frost protection, but can generate harmful condensation levels, so requires more effort at ventilating the tunnels. Obviously, the plastic isn’t permeable, so crops in the tunnel must be irrigated. The same spun bonded fabric used in floating covers can be used on the low tunnels, with similar levels of temperature and insect protection, but with greater accommodation for taller crops. Depending on the fabric weight, up to 80% of light transmission reaches the crop. Fabrics do pass rain water, and in fact, can reduce crop damage from very heavy rains. All tunnels must be opened to allow for pollination.
Kale grown under fabric (top photo), insect net (middle) and no row cover (bottom). Photo courtesy of Va. Cooperative Extension, Pub.HORT 291)
Beyond the benefits already noted, hoop-supported row covers have proven to reduce evaporation, resulting in less water use and less moisture stress in plants. In fact, numerous studies have documented superior vegetative growth in fabric-covered low tunnels compared with insect netting and uncovered crops as shown in the photo above.
Construction
Floating row covers require only a purchase of appropriate fabric. Fabric is available from good garden centers and many catalog and on-line sources. Weights range from about .55 oz. to 3 oz. The lightest are good for light and water transmission and general frost protection but are the shortest-lived. The heaviest are more for overwintering protection. Most come in rolls about 10 feet wide by 50 feet long or larger. With careful handling, a good quality fabric may last a couple of years.
Hoop-supported row covers use the same fabric. The 10-foot width fabric works well on my 4-foot wide raised beds. I cut ¾” diameter pvc tubing into 8-foot lengths. Then slide the ends over two ½” rebar pegs driven into the ground on each side of the bed. The tubing forms about a 3-foot high hoop, leaving ample clearance for the plants. The ten-foot wide fabric overlaps enough on each side of the hoops to provide a hold-down surface. A few photos illustrate this simple and inexpensive row cover system.
- Cut ½-inch rebar into lengths about 16-18” long. Length depends on your soil. The pegs need to find some hard soil to make a secure mount for the hoop, so if you are a raised-bed gardener they need to pass through your well-worked soil and into the hard pan below. They should extend above the soil surface by about 8 inches.
Photo: Slide ¾” pvc tubing hoop over ½” rebar pegs
- Purchase a roll of coiled ¾” diameter pvc tubing. Cut it with a hack saw to an appropriate length for your situation. I use 8-foot lengths for my 4-foot wide raised beds and get a 36-inch hoop height which is good for the greens I grow under them. Slide the tube ends over a pair of rebar pegs to make a hoop.
- Space the hoops 3-4 feet apart to support your fabric.
- Lay the fabric over the hoops, allowing enough overlap on the edges to provide an anchoring surface.
To hold the fabric on the hoops, make clips out of short lengths of the tubing. Cut tubing to a length of 4 inches or thereabouts and with a sharp scissors cut a gap along its length. Make the gap about a 3/8″– 1/2” long (see photo at left).
The tube is flexible enough to enable it to slide over the fabric and around the hoops, making a secure clip.
- Apply clips to the sides and tops of the hoops and add hold-downs to the ends of the tunnels, and you are in business.
Photo: Shows clips securing fabric to all hoops. Note rebar holding fabric on near end
The Benefits
I was driven to try row covers after losing a couple of kale and collard crops to cabbage moths. Not wanting to go the chemical route, they offered a way to get both an earlier start and good plant protection. In any case, they worked. Since the greens don’t need to be pollinated, the covers can stay on all summer and into the winter. The greens can often survive our winters without cover, but their dormant time is lessened by the row covers, allowing harvest for an added few weeks.
There are lots of ways to execute row covers, both purchased and do-it-yourself varieties. The one shown here is inexpensive, easy to do yourself. and quick to set up and take down. In any case, it works for me. If you have some hardy crops for which you would like to extend harvest, why not give them a try?
Sources:
“Season Extenders,”www.pubs.ext.vt.edu/426-381_pdf
“Floating Row Cover,” https://extension.umd.edu/hgic/topics/floating-row-cover
“Low Tunnels in Vegetable Crops: Beyond Season Extension,” www.pubs.ext.vt.edu/HORT-291.pdf