One of the most important developments in garden equipment over the past 10-20 years is the use of row covers. These are wire or conduit supported fabric covers that can either hold the heat on cold nights, or shade plants from the hot, mid-summer sun. They can also be an effective form of insect control. Garden suppliers now offer a wide range of hoops and cover sizes, making it possible to accommodate all kinds of plants, and it is not difficult to fabricate your own if you wish.
Fabric covers developed over the last ten years have a number of advantages over the earlier clear covers. First off, they are so lightweight (the lightest weight in at only a third of an ounce per square yard) that while they should be used with hoop supports, they don’t absolutely need it. These “floating” row covers are simply laid over the row, and the edges buried, leaving all the slack fabric loose over the plants. Multiple layers (or simply thicker materials) can provide significant frost protection.
As the crops grow, they pick up the row cover like the foil top on one of those pre-pack pans of popping corn. Also, since they are porous instead of solid, they allow the passage of both air and water, eliminating the need to provide ventilation and irrigation. But because they accelerate the growth of weeds as well as crop plants, you’ll want to put down a film mulch, or periodically remove the cover to cultivate the bed beneath.
Perhaps best of all, even the lightest floating row covers, if thoroughly sealed with soil around the edges, will keep out all kinds of flying insects. This function (as a pest barrier) alone more than offsets the fact that their manufacture is just as energy-intensive as that of plastic film mulches and row covers. Pest problems for which most gardeners would spray—with either a synthetic or an organic pesticide—can now be controlled with row covers. For example, a floating row cover placed over broccoli transplants, immediately after setting, is more effective in preventing cabbage root maggot infestations than the insecticide Diazinon; the same row cover will protect all kinds of plants from flea beetles, as well as keeping cucumber beetles from attaching squash family plants until they are large and vigorous enough to outgrow the attack.
Keep in mind, however, that many garden vegetables need to be accessible to insect to be pollinated. This requires removing the cover once plants flower (specific recommendations can be found in the individual vegetable crop guides).
Not only can row covers protect from pests and cold, they can provide protection from the heat, too. Lath and metal screening, as well as cheesecloth, have long been used to provide shade for cool weather crops when the temperature rises, but new woven plastic meshes are lighter, easier to install, and can be designed for just about any degree of shade. They are made of much more substantial thickness of plastic woven like burlap, and so will last for many seasons, though it still makes sense to store them in the dark during the off season to decrease the rate at which sunlight makes them brittle. Both the fabric and the woven mesh cloth covers are in the photo above.