Intermittent frosts during the fall can put you out of business long before they need to. A variety of row covers are available that can protect your crops from light frosts and even keep cold-hardy crops growing well into winter. But there are so many weights and types of row cover that choosing one to fit your needs isn’t simple. In general, you’ll be faced with a trade off between the frost protection you need at night and the light transmission you need during the day. Cost, handling and storage are other factors to consider, too. The most commonly available row covers in the United States are Reemay, Typar, Agribon, Agro-Fabric, and Covertan, which are all lightweight, spunbonded fabrics. There is also a Japanese product, Tufbell, made of a different material.

All come in several different thicknesses to provide different levels of frost protection. The lightest row covers weigh less than half an ounce per square yard, and provide very little frost protection. They are used more to exclude insects during summer. Moving up from there, weights can range from a half ounce to 2 ounce per square yard. As the weight increases, the level of frost protection increases, but light transmission decreases. Using the Agribon products as an example, AG-19 weighs .55 ounce per square yard and provides 4 degrees of frost protection with 85% light transmission. AG-30 weighs .9 ounce per square yard and provides 6 degrees of frost protection with 70% light transmission. AG-70 weighs 2 ounces per square yard, provides up to 8 degrees frost protection, but transmits only 30% of the light. The weight you choose, then, depends on what you’re trying to protect and how low you expect the temperatures to go before you have harvested the crop. For example, if you are growing fall spinach and you’re expecting a light frost, you can use one of the mid-weight row covers that allow adequate light for growth while providing a few degrees of frost protection at night. If nighttime temperatures routinely drop into the 20s, you may have to choose a heavier row cover and pull it off during the days to keep the plants growing.

Eliot Coleman, a pioneer in winter gardening, has been experimenting with various weights of row cover within his unheated hoophouses. He believes that light transmission is more important than a few degrees of cold protection, because row covers that allow the soil to warm more during the day seem to protect the plants as well at night as the heavier row covers. Tufbell row cover does a much better job of balancing frost protection and light transmission. When it’s held above the crop on wire hoops, it can warm the air 5 to 10 degrees, as moisture freezes within the fibers, creating an igloo effect that holds in heat. Tufbell transmits up to 95% of the light. The catch is that Tufbell is far more expensive than the other row covers, costing about 20 cents a square foot compared to the 1.5 cents per square foot for AG-19. Tufbell does last much longer than spunbonded row covers, though, so over time it may prove to be as cost effective as cheaper options. That’s especially true if you plan to use the row cover only for a short period of time, and then are able to store it someplace where it won’t be eaten by mice. Under those conditions, Tufbell can last five years or more. The manufacturer says Tufbell can be floated over crops, but it is quite stiff and can be used on hoops to make small, stable tunnels. Although row covers have been used for more than 20 years by commercial growers, there are still few hard-and-fast rules about which type is best.

Local conditions of wind, rain, and day to night temperature fluctuations make fall growing an unpredictable business. But the tools are there for doing your own experimenting into fall season extension. Sources Row covers are available from many mail-order seed and supply companies, including G&M Ag Supply, Harmony Farm Supply, and Johnny’s Selected Seeds, all of whose advertisements can be found elsewhere in this issue of Growing for Market. When you shop with these companies, please tell them you saw their ad in GFM. Technical details on row covers and names of local distributors can be obtained directly from the manufacturers:
Reemay and Typar – 800-336-8882; www.ken-bar.com
American Agro-Fabrics – 800-565-5151
Covertan – 888-786-8391; www.suntexcp.com
Tufbell – 800-949-8277