Fabric or plastic? Choosing row cover
Fabric, or plastic? That’s one of the most common questions that I receive about growing through the winter. Inquiring gardeners want to know — which is better?
My experience has shown that a single “best cover” for low tunnels doesn’t really exist — rather it varies depending on what is being grown, and even the lifestyle of the grower. In my own garden, I’ve experimented with various combinations of fabric row covers and clear plastic sheeting, growing replicates of plant varieties under these various conditions. What have I learned? You can be a successful winter gardener with either setup.
But there are some situations when using clear plastic sheeting as your cover of choice will doom you to failure, and other situations when improperly-selected fabric covers can be catastrophic. How can you know which cover is best for you? Here are five questions to consider.
Please note: I receive no compensation by sharing most of the following links — they’re here purely for your convenience. Clicking on an affiliate link, marked with an asterisk (*) cost nothing extra to you, but I receive a small advertising fee that helps me keep this blog up and running.
1) Can you get in the garden every day?
This is the most important question to ask yourself when choosing a row cover. Whereas fabric row covers are permeable to air and therefore self-venting, tunnels covered with clear plastic sheeting will need to be continuously monitored and vented on sunny days. Tunnel temperatures can easily reach 90 °F (32.2 °C) in winter, even when the day’s high is only 30 °F (-1.1 °C). And don’t think you’re doing your plants any favors by keeping them warm. Warmer temperatures promote disease development in the humid conditions of the tunnel, and also trigger plants to lose the sugars and other cellular adaptations that they’ve accumulated to withstand freezing temperatures (recall that tunnels don’t prevent nighttime freezes — they just help plants survive them).
How warm is too warm? I vent my tunnels as soon as they begin approaching 65 °F (18.3 °C). I’m lucky enough to work near my home, which allows me to walk home quickly if the day’s weather deviates from the forecast. If you decide that a clear plastic tunnel is within your abilities, I highly recommend purchasing an inexpensive remote thermometer like this one.*
I also monitor tunnel temperatures from anywhere with an internet connection, using a great weather station similar to this one* that transmits data to a private web address.
2) What is your plant hardiness zone?
Most people assume that glass or clear plastic is the only option for winter gardening, but fabric row covers can work well for most of us here in the United States. If your winter nights only rarely dip below 0 °F (-18 °C), then fabric row covers are a great option if you’ve realized that clear plastic won’t work for your lifestyle. I use medium-weight fabric row covers on the majority of my beds here in the eastern Kentucky mountains (zone 6b), successfully growing vegetables like carrots, radicchio, baby Asian greens, chervil, young fava beans, winter radishes, and mache all winter long. I’ve even grown lettuce in this way, doubling up the fabric when temperatures turn exceptionally frigid, such as during last year’s Polar Vortex.
3) What do you wish to grow?
I reserve the space under my plastic-covered low tunnels for vegetables that are less tolerant of hard freezes. Whereas immature Asian greens like tatsoi or michihili cabbage easily survive hard freezes under fabric row cover, mature stages turn to mush (especially thick-stemmed varieties like Pak Choy). The same is true of other mature vegetables, including Swiss chard, lettuce, fava beans, lacinato kale varieties, and Hakurei turnips. So if you want to have salads all winter long, but cannot use clear plastic, simply time your sowings so that plants are baby-leaf sized and able to survive under fabric row cover alone. Baby Asian greens and kales make phenomenal winter salads, and are much more nutrient-dense than lettuce as well.
In addition to baby greens, there are a number of other plants that are remarkably hardy in sub-zero weather. Try this Top 10 list of cold-hardy vegetables to get started growing under only fabric cover.
4) Are you winter gardening, overwintering, or winter sowing?
What is your goal of growing in the winter? Much of what I’ve discussed refers to winter gardening, with the goal of eating fresh food from the garden all winter long. But what if you just want to get a head start on spring? Choose overwintering varieties of cabbage, purple sprouting broccoli, and onions, which are usually planted in the late summer, grow all winter without protection (or under fabric row cover), and produce in the early spring. Or try winter sowing by direct-seeding spinach, beets, fava beans, or greens under the protection of a fabric or plastic tunnel — young seedlings will grow slowly all winter, and growth will take off when the longer days and warmer temperatures of spring arrive, putting you months ahead of your neighbors.
5) How much snow cover do you receive?
Snow should be removed from both fabric and plastic tunnels, or the additional weight can cause tunnels to collapse. Snow removal is easily accomplished with a broom, though it slides off most easily from plastic-covered tunnels and therefore takes less time. However, plastic-covered tunnels may require venting soon after a snowstorm has passed, which can be difficult to do when the edges are covered with a foot of snow. Indeed, last winter, I was shoveling snow frantically in order to vent my tunnels after a heavy snowstorm, as temperatures had already reached 85 °F (29 °C) inside them by noon the next day.
I hope this has helped you find the cover that is right for you. Now, here are some helpful links to help you find them:
Sources of Fabric Row Cover:
Agribon fabric row cover comes in various weights, which influences not only the degree of freeze protection, but also how much light reaches plants. Because reduced light is a major factor limiting plant growth in winter, I recommend that you choose no heavier than Agribon-30, perhaps doubling up the fabric on especially frigid nights. If your winters rarely dip below 25F, lighter weight Agribon-19 is a better choice for you. You can buy Agribon in small lengths more suitable to home gardens from Amazon,* or get larger rolls of it from Johnny’s Selected Seeds.
Although I’m a faithful Johnny’s customer, I’ve switched to this company for supplying my fabric row cover; they are based in my home state and offer an alternative to Agribon that is less expensive and more durable. You’ll need to call and request a catalog from them the old-fashioned way, as they don’t offer internet sales, but I can speak from experience that their service is outstanding. Deerfield Supplies, 2825 Stringtown Rd, Elkton, KY 42220, United States. (270)-265-2425
American Nettings and Fabric
This company sells shorter lengths of fabric row cover, primarily for the home gardener.
Sources of Clear Plastic Film:
Clear plastic sheeting is available at most hardware and home supply stores. UV-treated greenhouse film is more expensive, and not really necessary, since the reduced intensity of winter light isn’t as damaging to the plastic (I’ve used my uncoated construction-grade plastic several winters). However, if you desire UV-treated film, manageable rolls are available from Johnny’s Selected Seeds.