By Janelle Daberkow
Extension Educator, Stearns and Benton Counties
Row covers come in various sizes, are made from various materials, and are used for different purposes by vegetable growers. Row covers include plastic covered trenches, floating row covers and hoop-supported row covers. They are made of light-weight materials such as polyethylene (poly), polyester or polypropylene, and may be vented or unvented. Vegetable growers can use row covers to drape over individual plants, or enclose plants in rows or groups. The cover "floats" directly over the top of the crop, allowing air, sunlight, and water to penetrate the material, but protecting plants from outside pests. Plants beneath row covers without vents are often irrigated with drip irrigation. Floating row covers can be purchased through mail order seed catalogs as well as from garden supply companies and at some local garden centers. An advantage of using row covers is that they can usually be reused for two to three years.
Row covers made of heavier materials can offer frost protection to crops in the fall, and also allow for earlier season plant establishment in the spring by holding temperatures 4- 10 degrees warmer under the protection of the row cover. Crops, such as radishes, lettuce, spinach, broccoli, cabbage, cauliflower, peas, Chinese cabbage, beets, carrots, turnips and parsnips, can be seeded directly into the garden and covered at planting time by the row cover. Row covers made of lighter weight materials can be used as a pest barrier around plants by keeping insects, rabbits, deer, birds and other nuisances out.
Row covers can be secured to the ground with sod pins, boards, bricks, sand bags, rocks or soil. It is important to leave enough slack in the row cover so that growing plants can push it up. Plants that are well suited for row covers include: lettuce, spinach, radish, broccoli, cabbage, carrots and cauliflower. Other crops such as Swiss chard, beets, potatoes and snap beans can be grown under row covers, but since are growing through the hottest part of the summer and it may be necessary to remove the row covers by mid-June to prevent heat from building up around plants.
Some disadvantages of floating row covers are that pests that overwinter in the soil can become trapped under the row covers. These pests include: aphids, whiteflies, mites, trips, root maggots, flea beetles or Colorado potato beetles. Cultivating the soil before planting to reduce the number of surviving insects, and rotating crops from year to year will help with insect populations. Temperatures under floating row covers can increase dramatically, and temperatures can become too warm during hot days for plants. Also, weeds grow fast under floating row covers. It is necessary to pull the row covers back to hand-weed or hoe weeds out. It is possible to apply mulch around plants to keep weeds down. Finally row covers are difficult to use with tall plants, and covers need to be removed from plants such as tomato, pepper and eggplants, cucumbers, squash, melons, and pumpkins, when they begin to flower.