Spring Weather and Row Covers
Posted: May 3, 2012
Spring Weather and Row Covers
(K. Demchak, Dept. of Horticulture)
This past summer, fall, winter and now this spring - have been unusual. One item that can help growers deal with the weather changes, at least for plants that are close to the ground, is a floating row cover. There are many different types from which to choose.
Row covers can protect strawberries from cold and wind during the winter, can be used for frost protection on small areas, and can help protect tender plants if you decided to get a head start on planting. Some considerations when purchasing row covers are row cover weight, insulation ability, durability, cost, and light transmittance.
Weight: A heavier row cover would be expected to provide more protection and also be more durable, if all other characteristics were similar. However, comparing the same weight of row cover among different manufacturers is somewhat akin to comparing apples to oranges, as similar weights of row covers from different manufacturers can provide different amounts of protection. It’s often better to compare the degrees of protection that a manufacturer says you can expect from a row cover, rather than going strictly by weight.
Insulation ability: As mentioned, this is not strictly related to weight. One big factor is stiffness and structure of the fabric. Softer fabrics tend to insulate better as long as they are dry. They also tend to flatten down and mold themselves to the beds when they get wet, and then don’t provide much protection. Personally, I’d rather have a stiffer fabric because I know what to expect out of it - since it performs similarly wet or dry. Also, in my experience, a double layer (even if the bottom layer is an older row cover) provides much more protection than a single layer of the same fabric, and often more than a single layer of a heavier fabric.
Durability: This is one of the top considerations. Row covers that can be used for multiple years are generally a good buy, even if they are more expensive to start with. Just because a row cover is heavier is not a guarantee that it will be more durable. Durability is more closely related to the structure of the fabric. Some have reinforced edges, and others are reinforced within the fabric itself.
Cost: Generally this is related to heaviness of the fabric, but not entirely, and as already mentioned (more than once) row cover weight is not strictly related to durability. It’s worthwhile to compare the cost of the row cover on a yearly basis over its expected life, rather than considering just the up-front cost.
Light transmittance: The manufacturer should have data on the amount of light that a row cover allows through. In radiational frost events – nights with a clear sky, a row cover that allows sunlight through (even down to 60% transmittance is OK) can result in a few degrees more protection than a heavy one that does not allow much light through (30% transmittance) – if you are in a situation where black plastic mulched beds can gather heat during a sunny afternoon.
Do I have a favorite row cover, you ask? I probably can’t endorse a particular manufacturer, but at least for now, there’s a midweight (1.25 oz) row cover that I like that has the light transmittance of a relatively light cover, the protection of a midweight one, and excellent durability. You also might want to talk to other growers to compare notes on performance.
By the way, if you are wondering what else to plan for… NOAA long-term temperature and precipitation forecasts can be found at http://www.cpc.ncep.noaa.gov/products/forecasts/ . You can just click on the time period you are interested in once you get to that page. For some time period choices where you have a choice of maps or text forecasts, I find the maps are easier to understand quickly. Remember that the forecasts are compared to “normal”, so you need to be keep in mind what “normal” is (or was).