Hands-On Gardener: Cover Up

by Miriam Hansen

Do you wonder why your neighbor’s garden is covered in white billowing material? Have you been wondering what that stuff is, and why more and more people are using it?

The “stuff” is variously called row cover, floating row cover, frost barrier, garden or frost blanket, or Reemay. The latter is a complete misnomer. Reemay is not the stuff itself. It is a brand and perhaps not the best brand available anymore.

Let’s just call it row cover. Made from spun-bonded polyester or spun-bonded polypropylene, row covers are so lightweight they can be loosely laid over a bed without fear of crushing seedlings. The cover has to be loose so the plants have room to grow, pushing up against the cover as they do so.

Because row covers are so lightweight, they have to be firmly anchored top, bottom and sides to prevent the cover from blowing off and insects from getting inside. We use large rocks as anchors. We have rocks in abundance. You can also pile soil along the sides, bags of sand or soil or even sticks.

The beauty of row covers is that they allow moisture, sun and air to penetrate while offering protection from low temperatures, insects and wind. We use them to protect early brassicas from flea beetles and squash from cucumber and other beetles. In addition to pest protection, row covers raise day and night temperatures enough to significantly improve growth and yield. I’ve seen this time and time again where I’ve had only enough row cover to partially cover a bed. The plants under cover outperform the plants that did not have that additional heat.

Where we use row covers all season, over beds of basil and peppers for instance, we stretch the material over plastic hoops anchored on short pieces of rebar to make a kind of low hoop house. I prefer this system to laying the cover loosely right on top of the plants, particularly when growing points are going to project right up against the material. I find the optimum width for my garden beds, particularly where I use hoops, is a six foot width.

We spray with a full spectrum insecticide like pyrethrin right before we cover the bed. This ensures that whatever has already found the seedlings—and let’s face it, the flea beetles and cucumber beetles are not politely waiting to the side while we arrange the cover over the bed—will be dead, and we’ve pretty much ensured that no new pests can get in. This makes securing the sides particularly important. Don’t stint on rocks or whatever you’re using to hold the material in place.

Also, be aware that this stuff is incredibly easy to tear. Take care not to catch it on wire or twigs or anything that will shorten its life. Treat it gently, and it will more than earn its way. Even after a piece is torn, you can shorten it, clothes-pin it together, even sew it back together, though I’ve never tried this myself. We use the same pieces year after year until they have pretty much disintegrated.

You can leave row cover on a crop for the entire season, and in the case of a heat-loving plant like basil, that is a good idea. But, if you are using row cover over fruiting plants like peppers, eggplant, tomatoes and squash—in short anything that flowers—you have to take the row cover off from time to time to allow the pollinating insects to get access to the flowers.

Row covers come in different thicknesses. Some offer no frost protection at all but the benefit of pest protection and around 90 percent of sunlight. The thickest can reduce sunlight to 50 percent but give enormous frost protection—up to 8 degrees!

In general, I look for the median weights. It gives me the best of both pest control and increased temperatures and allows more than enough light in. If I need additional protection for a hard frost in the fall, we put an extra layer on. We take the second layer off when temperatures rise above freezing and put it back on if necessary at night.

We also use row cover in our one-ply plastic greenhouses. When the temperature in the greenhouse is around 25 degrees, I know the seedlings under the row cover are still above freezing. That is one place a heavier blanket like Dewitt Supreme (Guy’s Farm & Yard) is a good investment. It takes you down to 50 percent light, but greens are not fussy about light in the winter. With 8 degrees protection, the increased temperature compensates for lower sunlight. One gardener who uses this weight on her sweet potatoes says, “These heat-loving plants really thrive under this frost blanket. The reduced light doesn’t make a bit of difference.”

I hope this has not utterly confused you. In general, I look for median weights (something like Agribon 19), wide enough so my plants can grow to four feet or so (six or so feet wide). I weight the material securely on all sides to prevent pests and wind from either sneaking in or ripping the covers off: use hoops if you want to keep the row cover on when plants are going to press up against it, and remember to remove the cover periodically to allow pollinating insects to have access to the flowering plants. You can find these materials at most local gardening centers and online from most seed supply houses like Fedco, Vesey’s and Johnny’s. That’s pretty much it.

Now cover up! And happy gardening!

 

Miriam and her husband, David, live in East Montpelier, where they grow most of their own vegetables, berries and meat on less than one-quarter of an acre. Your questions and comments are welcome. You can reach Miriam at freshair460@gmail.com.

 

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