"Row Cover Technology"
by Lucy Goodman
What are Row Covers and Why Should I Use Them?
A row cover is simply a piece of cloth that growers use to cover plants for either frost, weather or insect protection protection. They come in many sizes, thickness' and materials. They are cut to fit a row or bed laid on top of the plants or on hoops, anchored with rocks or other material and they than can keep hail frost or insect at bay. They are not always easy to handle especially the first season or two-there is a definite learning curve with row cover technology but they are a good answer to a lot of potential problems to the sustainable grower such as protection from weather, keeping moisture in the soil, better germination in seed starting, season extension, Protection from ag chemicals, Protection from cross pollination (must hand pollinate) and insect protection. We have really lowered our use of such insect controls as Bt since using row covers and have almost no damage due to insects or weather on our salad and other greens
Different Types of Row Cover
Spun Bonded Poly Propylene-These are probably the most common row covers in use today. These come in a variety of weights and are made by several manufacturers. These are good year round for weather protection, insect protection and preventing the soil from drying out in drought conditions
Cotton-Elmer Plantex-C-resembles cheese cloth. Good for insect protection and won't burn plants but gives only a few degrees of frost protection. Can be composted. Expensive and hard to find
Slitted Plastic Slitted plastic is self venting so can be used in warm temps. Great for season extension especially early spring time plantings.
Solid plastic is good for season extension in cool weather but can heat up too much on warm sunny days and kill plants, Best in late fall/winter especially combined with spun bonded covers. Be sure to use a UV stable plastic such as Tufflite (i.e. greenhouse plastic)
Tufbel This is made from polyvinyl alcohol (PVA). PVA has unique absorption properties which allow moisture to freeze within the rowcover fibers and form a protective shield, like an igloo, over the crop. Yet PVA is also breathable (35% permeable), allowing crop ventilation during the day. You can water or spray right through it, without need for removal. The draw back is this stuff costs almost 10x more than spunbond polypropolene covers, does not last 10x longer and is hard to find.
To Hoop or Not to Hoop?
Most plants don't like the weight of covers on them so it is advisable to use hoops. The Length to cut the material depends on the width of your beds and the height of the plants to be covered. For wire I use 8' lengths for 4' wide beds and 2' high hoops. PVC and conduit come in 10' lengths so that is the usual length used for those materials. Hoops are very important for season extension as plants touching row cover will get frost damage
Seed beds can have the covers put right on the soil. The covers keep moisture in the ground and greatly aid in germination
Wire I use #9 gauge wire which can be bought in bulk at any farm supply store. These are thin and tend to fall over in very wet conditions but they are cheap and don't leach chemicals into the soil
PVC Pipe which needs to be anchored with rebar are wider than wire and don't damage the covers as much because of the width of the pipe. They are also less likely to fall over. PVC can leach chemicals into the soil though, is tough to dispose of, may cause chemical reaction with UV stable plastics, is not UV stable so will degrade in 2 or 3 years and it not structurally strong. needs to be used with rebar anchors
Conduit (metal) is sturdy, long lasting but initial cost is more than PVC (though over 10 years costs become cheaper than PVC). It is not reactive with any plastic. Needs to be used with rebar anchors
Anchoring the Covers
Covers have to be anchored well anyplace there is wind. One of the biggest hassles with covers is wind and poor anchoring. Over the years I have tried many ways to anchor the covers.
Bricks and Rocks Bricks or large rocks (5 to 10lbs) spaced every 3' or so. If there are big winds (25 mph+) I space the rocks every foot. The big advantage is they are cheap and usually plentiful.
Fence stakes these are heavy and long and do a decent job of keeping covers in place but they tend to rip the cover, they're heavy and hard to move for some.
Soil digging a shallow trench and burying the edges of the covers. This does a great job of holding covers in place but it is hard to move covers for maintenance or harvesting.
Spring Clamps/Cloths Pins Works decently but expensive (spring clamps) and covers tend to rip where clamped. Use spring clamps with PVC or conduit and clothes pins with wire
Staples These are U shaped wire you stick in the ground to anchor covers. These tend to be pricey. Some folks love these things and other hate them.
When to use Row Cover
Covers can stay on plants the entire summer. The covers keep drying winds off of the plants, keep moisture in the soil and keep the median temp at at around 8o˚F to 85˚F. A 2003 study by a Spanish group of researchers found that crop quality and yields were better under covers than plants exposed to the elements. We found during the hot and dry summer of 2002 that most our crops did much much better under covers than those without covers. We found the year before that broccoli planted in June and left alone with an agri-pro 19 cover on it did not die of heat stress, despite summertime temperatures going well over 95˚F, and ended up producing a bumper crop of fantastic broccoli that fall. The cover had been left on by mistake but what a wonderful error! We found that the 35 and 50 weight (winter weight) covers were more effective than the lighter "summer" weight covers.
We did have a few failures. Aphids got under the covers and destroyed the turnips in about 3 days and a big hole in a bean cover allowed bean beetles and cuke beetles entry where they ate an entire 50' row in under 4 hours (the beans were ready to pick and beautiful too) but no problems due to heat stress.
Most flowering plants need pollination and the covers should be removed about a week before the flowers bloom so the pollinators can find them or leave them on and hand pollinate the crops daily. The covers can be put back on after pollination but the area should be checked carefully for insects before reapplying. If there are pest insects (and there will be) you may want to either leave the covers off the rest of the season or apply the pest control of your choice after the covers are back on. If you leave the pests be under the row cover you will at the very least have heavy damage to the crop if not a total loss.
Row covers go on as soon as the seed or seedling is planted. Be ready by having all materials (hoops, rocks, any irrigation) with you when transplanting so that it is easy to apply the covers ASAP.
For season extension the covers need not be removed except for maintenance and harvest. They need to be put on before the freezing weather happens
The work great in conjunction with unheated hoophouses. Every layer over the plant means a higher (warmer) growing zone. So if you live in zone 5 and put a heavy cover on your plants you have taken them to zone 6. If you put a hoophouse over that you have taken them to a zone 7 environment.
Row covers do not work well in snowy areas. The snow tends to mash down the hoops, leaving the covers flat on the ground. This does not usually hurt the plants in any way (snow makes a wonderful mulch) but it is impossible to remove the covers for harvest without destroying the covers and possibly the plants.
Problems with Row Covers
There is a learning curve with Row covers. They are not easy to use at first but with time they become indispensable. Still there are problems.
Insects; Aphids and flea beetles love the row cover environment and can decimate a crop quickly. For flea beetles I use a bottle (I like 16 oz/1 liter water bottles, 2 liter bottles tend to fall over) filled with water and covered with Tanglefoot™ to control the flea beetles. The water warms up during the day and at night the bugs are attracted to the heat and get stuck. Aphids I have tried introducing lady bugs with limited success. Any insect caught under a cover can become a problem quickly so it is good to check for them often. In 2002 we tried vacuuming insects from under covers with fair success. We used both a hand vac and the vacuum on our 8 hp chipper shredder.
Anchoring If they are not anchored well they tend to blow away or at least rip themselves to shreds-this is the hardest thing to learn, in my opinion. The covers need to be applied squarely and be pulled tight from end to end to stay on well in high winds
Animals Animals will punch holes in them especially if they are on hoops. We have cats that love to jump into them and form large holes. Deer will also walk through them once they get use to them, leaving hoof holes behind.
Disposal They are made out of plastic and hard to dispose of ecologically.
Out of sight, out of mind. It is easy to not check plantings under row cover as often as one should. Both weeds and insects can get out of control under covers. Simply setting up a schedule for looking under the covers solves this. They must be removed and than reapplied to foliar feed. this makes the job of foliar feeding either twice as long to do or a two person job
Despite the drawbacks, row covers are an essential on our farm for insect protection, weather protection, a germination aid, season extension and improvement in crop quality and yields.
Web resources High Tunnels. Org A nice site with tons of season extension/hoophouse information
The New Organic Grower Eliot Coleman copyright 1989,
1995;ISBN 0-930031; Chelsea Green Publisher, White River, VT
Growing for Market(periodical)
PO Box 3747
Lawrence, KS 66046
Acres USA (periodical)
PO Box 91299
Austin, TX 78709
Sources for Row Cover
Johnny's Selected Seeds
955 Benton Ave
Winslow, ME 04901
PO Box 520
Nolt’s Produce Supply
152 N. Hershey Ave
Leola, PA 17540
(717) 656 9764
(Amish company, no website)
5100 Schenley Place
Lawrenceburg, IN 47025
FAX (207) 872-8317