Row Covers – what, whow, when, why do you need them?
Row covers serve several purposes in my garden. I sometimes purchase row covers by the yard off a big bolt, or I raid the linen closet for old sheets. No need to be too fancy, the plants don’t care. Covers hold in a few degrees of warmth at the beginning and end of the growing seasons, can provide shade from summer’s extreme sun, and block insects from tender seedlings.
I like Agribon. It’s tough enough to be used multiple years but light weight. It’s available in a variety of weights/thickness.
Floating row cover is the simplest cover to use. It doesn’t need to be supported on a frame. It’s so light weight the plants will lift it as they grow. You can start using a floating row cover in the spring while plants are still small but watch to be sure the cover isn’t bending the seedlings over.
Some covers are thick enough to keep seedlings protected from frost down to 24° and let you start hardy seeds from peas, spinach and beets unusually early. The down side of heavier covers is that let only 50% of sunlight through instead of the typical 85% so switch to a lighter cover as soon as possible. Place the row cover over the row and weigh it down on the ends. You can purchase U clips to push through the cover and into the soil, use odd pieces of lumber (which will also make picking up slugs and other pests simple each morning) or use rocks. Any heavy object will do.
Row covers aid in seed germination by keeping the soil moist. Tiny seeds such as petunias or carrots can dry out quickly and die. Moist soil protects against crusting, something that happens when the soil dries out and becomes hard and thick at the surface.
Prevent a problem with spring pests by using row cover as an insect barrier. Keep sides and ends closed and weigh down the cover all around to block the insects from crawling under. Look for pests that have emerged from the soil underneath the cover so you don’t trap in what you’ve worked to keep out. If you find pests you can pull back the barrier, remove the pests, apply the appropriate insecticide, and replace the barrier. Be sure to check again the next day and continue to check while the row cover is being used.
I use floating row cover to control cabbage worms (broccoli, cauliflower and cabbage), carrot weevils, Colorado potato beetles, cucumber beetles, flea beetles (not as much of a problem in summer as in spring), leafhoppers, leaf miners, squash vine borers, birds, rabbits, woodchucks and even an occasional goat that has escaped through the pasture fence. You need to continue to check for insects trapped under the row cover. Avoid a heavy row cover that will hold in too much heat during the summer. Stick with a light weight spun bonded polypropylene.
If you use a heavier row cover like slitted plastic you need to check the temperature under the plastic daily. Even heat-loving plants can get too hot under cover.
Shade helps protect the plants and soil from the sun. In this case, place three foot wide row covers over low tunnel ribs and secure with clips. Air flow won’t be blocked but the sun won’t be quite so harsh.
When the temperature is above 60° during the day I recommend pulling the sunny side of the row cover up to allow for air circulation and avoid over heating the plants. When the temperatures rise to 80°, such as during an Indian Summer, push the row cover all the way off to one side for the hottest part of the day.
If it’s windy you should tack the cover down in a few places. A flapping cover can do a lot of damage in a short time. Replace the cover in late afternoon so that the ground stays warm. I use row covers in the fall on lettuce, peppers, bush beans, squash, pumpkins and other plants that appreciate the extra warmth. For radiant heat add large rocks between plants to absorb heat during the day.
Beware of Frost
Frost protection is very important once the night time temperatures start dropping. It won’t hurt to cover your flowers and vegetables “just in case” there might be a frost. If you don’t hear a frost warning until the 6 o’clock news don’t worry. Grab your extra sheets! They’ll fit over tomatoes in cages, patches of squash and pumpkins and just about anything else you might need to cover. Save your covers for the frost sensitive plants. You don’t need to cover broccoli, cauliflower, cabbage, Brussels sprouts, turnip, kale, spinach, rutabaga, carrots and other cold hardy plants. They’ll take a light frost and sometimes a heavy killing frost without being damaged.
After the frost melts and the air starts to warm you might remove the cover, but it may not be necessary. If the cover is light weight and allows sun and water through, and the temperature isn’t going to be too warm, you can leave the cover on.
You might have heard of high tunnels being used by commercial flower, fruit and vegetable growers. Backyard gardeners often use another version called low tunnels. They’re around four feet wide and up to four feet tall.
Use slitted row cover, heavy-weight poly with pre-cut slits, in early spring and fall. Support it with No. 9 wire cut to the appropriate length to match the height and width of your tunnel. Each end of the wire is pushed into the ground to form the hoop. The slitted cover is stretched out the width of the row plus an additional three feet on each end. Weight one side to hold the plastic down. Stretch it over the hoop and cover the other side. Close in the ends. As the plastic warms and becomes flexible it will relax, opening the slots and releasing heat. If the temperature rises too much you need to open the end to increase circulation or lift one side of the poly. clip the plastic onto the wire with clothes pins.
Low tunnels are particularly helpful with heat-loving plants like tomatoes and okra. Keep in mind that slots don’t close completely. A lot of heat is lost through the top during the night. If it’s going to be too cold over night you should use a sheet on top of the tunnel. It doesn’t have to cover the entire height of the tunnel. You can cover six inches below the slots. Again, clothes pins will attach the second cover for the night.
Cucumbers, melons and squash can be transplanted into the soil and covered with a low tunnel to give them an early start in the spring. These are plants that don’t like cold feet. The soil temperature needs to be warm enough to keep them happy before you transplant the seedlings. You can warm the soil by spreading strips of clear plastic over the row and anchoring it down tightly. Clear plastic allows sunlight through to warm the soil faster than black plastic. Black plastic absorbs the sun’s heat then warms the soil. When the soil has warmed you can roll your plastic up and store it for next year’s use. Make your low tunnels and transplant your seedlings at the same time you remove the plastic.
End of Season
Inspect your row covers carefully. Cuts in poly covers can be repaired with greenhouse patch tape. Make a straight cut the entire width of the cover at the edge of a rip You’ll have a shorter piece of row cover but you’ll be able to save and reuse it next year. Store cloth covers like spun bonded polypropylene in hard plastic containers to protect it from rodent damage.
Throw away row covers if they covered diseased plants. Better safe than sorry.