Row Covers 101
Prepare for spring planting by getting row covers ready, so you can plant earlier and plan for a longer season.
Prepare for early spring planting by getting row covers ready.
Extending your seasons is a great way to get a jump on spring and farm later into fall. One way to do this is by using materials on both ends of the seasons that will allow you to either plant earlier or continue growing later than would otherwise be possible due to cold or frost. This will also allow you to grow varieties you might not generally be able to in a colder region. As well, depending on your locale, some of these materials can be used to overwinter crops.
One of the largest categories of season extension materials is termed “row covers.” Search “row covers” (aka “Reemay”) online or in garden catalogs and a long list of brands and types will be found. What’s the difference between Typar and Agribon? Ag-15 versus Ag-30 versus Ag-50? What size do you need? Floating row covers or supported?
As this stuff isn’t cheap and the well being of your crop depends on it, having a good idea of which products will meet your needs is important. Season extension works for the smallest home garden to large market grower fields, with products and sizes to suit. It can help a grower in northern Vermont protect their tender annual veggies against an early fall frost as well as allow a Georgia grower to keep plants producing throughout the entire winter. Follow along while we take a closer look at what’s out there.
Cover Coverage
Row covers are generally made of a spunbonded polypropylene material. They are found in many “weights” ranging from those that provide insect-protection only to heavy row covers used to overwinter certain crops. Depending on their grade and manufacturer, they exhibit specific levels of light transmission and frost protection, rated by degrees of frost protection.
Row covers designed specifically for protection of crops from insects (flea or cucumber beetles, etc.) are designated as lightweight insect barrier. Common products include Ag-15 and Proteknet insect netting. While an excellent product, these don’t provide frost protection. They should only be used to protect crops from insect damage or to deter grazing of crops by deer and other wildlife.
The next level up provides some frost protection. A commonly used product is Ag-19, which provides between 2 to 4 degrees Fahrenheit of frost protection, protecting the crop down to 28 degrees or so. This product is also often used at the beginning of the season to cover heat-loving crops that could use the added warmth such as eggplants, peppers, melons, squash, beans, etc. It permits 85% of light to pass through, known as light transmission. It also allows some rain to permeate the cover.
I used to use this product a lot, but just this year, I switched to trying out Covertan Pro 19. This row cover provides the same amount of frost protection but allows more light transmission (approximately 90%) and rain through and is stronger than Ag-19. I plan on switching over to only Covertran as my Ag-19 wears out. In either case, whether you use one or the other, buying the correct width and length is important as is installation. The information that follows is valid for either brand as well as any others of similar weight/ frost protection rating.
Know Your Dimensions
In general, you’ll achieve cost savings by buying longer lengths of row covers rather then the short pieces commonly sold at garden centers. The caveat here though is that the longer the row cover, the more likely you are to incur higher shipping charges. A 50-foot length of Ag-19 might not trigger extra shipping charges, but a 250-foot length almost certainly will. You need to weigh the cost/foot including shipping charges to figure out the best deal.
As well, how big an area do you need to cover? I only buy longer lengths of row covers and store the extra. The row cover needs to be able to solidly connect with the ground and be anchored to it without gaps in order to be most effective. When in doubt, go for wider. Remember that your plants will grow considerably over the season. If you wish to use row covers to protect tomatoes that are tied to stakes or in wire tomato supports, you will need a wide row cover. Measure from the ground, allowing a generous amount to anchor to the soil, up the side of the supports, over and down again.
What about floating row covers versus supports? It depends on the crop being protected. In general, crops do better if the row cover (used for frost protection) doesn’t come in contact with the foliage or fruit. As well, crops that have sharp pointy parts such as peppers and eggplants will often tear holes in row covers unless hoops support them. I tend to use hoops
to protect crops such as peppers, eggplant and beans while using floating row covers on those such as melons, squash, cukes and strawberries. In the spring, I often start out using hoops to protect the cucurbits, but by later in the season, when they’ve gotten large, I switch to floating row covers.
While there are homemade hoops that some people construct out of PVC pipes, and some use small short stakes to support the row cover, I prefer to use standard wire support hoops. These are generally made of a No. 9- or 10-gauge metal. I purchase them in large quantities, storing for later what I don’t need at the moment. The shipping charges for precut wires are high due to their length, but they’ll last for many years if well cared for. I tried buying some coils of wire online to cut my own, but this was a failed endeavor as the wire that was sent to me wasn’t usable to make hoops. I’ll use it to trellis grapes or for fencing at some point. They often come in several lengths but I prefer 76 inches. Better to have excess wire than for it to be too short!
Ground Support
There are many methods of anchoring row covers so they’re sealed to the ground and don’t fly away. Some of it depends on how often you wish to open up the row covers. If you plan on allowing the row covers to stay in place for some time, anchoring them to the ground by shoveling soil over their edges works well. This method is often used for anchoring insect-grade row covers securely to the ground to keep out insects.
Some people use rocks to hold down the row covers although a truism seems to be that there are never enough rocks around when you need them! Others fill small bags with sand or soil, which they use to secure the row covers.
I tend to use a combination of rocks and earth staples. These are U-shaped metal pins, found in lengths between 3 to 6 inches. I prefer to use the 6-inch lengths for better anchoring strength. They can be bought in small packages or in boxes of 500 or so online, which is how I purchase them. Again, they can be reused from season to season, and if stored properly, you’ll have them for years to come. Ordinary clothespins are also handy in helping anchor fabric to hoops or to join lengths (or widths) of fabric if needed.
A technique I sometimes use is to double up my hoops so that I insert two wires into the ground, immediately adjacent to each other. Then I weave the row cover under and over each time I come to a set of wires. This helps anchor the fabric even more and can allow me to easily just push up one side to weed, allow for pollination, ventilation, harvest, etc. instead of removing the entire row cover.
Overwintering
Row covers are available for overwintering of specialty nursery crops, strawberries or greens. The heavier the weight, the less light transmission occurs and the more they cost. I used a row cover comparable to Ag-30 to cover my strawberry planting for the
winter when I was farming in central Vermont. This was in lieu of covering with straw. It worked quite well and the plants did fine.
For my small home garden strawberry planting, I plan to use Ag-19 or Covertan-19. I’ll use it as a floating row cover, placed directly over the plants. I’ll pull the row cover off in the spring to weed and fertilize and pull it off for good once flowering starts. This will give my plants a head start. It’s been estimated that one layer of row cover moves you one USDA ag zone warmer, so this will make my barely zone 4a feel more like a “balmy” 5a to my strawberry plants.
With just over a 90-day frost-free growing period here in my location, I’m also playing around with tricks to improve the yields of heat-lovers such as melons, eggplants and peppers. Using row covers such as Covertan-19 in the spring and removing it only once the plants are in bloom helps. Next season, I’m going to try removing the row cover from the melons only long enough to get a certain number of flowers pollinated and then recover them until it’s time to harvest. This should push the plants to develop what is already pollinated instead of continuing to produce fruit, which won’t have time to ripen.
Heavy covers — such as Ag-50 and Ag-70, as well as Typar, which makes a good row cover, too (the row cover material, not building wrap!) — are used to provide between 5 to 8 degrees of frost protection. One use for this is to overwinter nursery plants in containers. Another is to cover greens or carrots during the
winter. In some climates further south, this is all that is needed to keep them growing and to be able to harvest crops even in the winter months. In cold climates, this can allow a young leafy green crop such as spinach or kale to remain in the ground and resume growing in the spring, way before a seeded crop.
Layered Support
Sometimes row covers are used along with other methods of crop protection such as cold tunnels or cold frames. A low or high tunnel, covered in plastic, can shelter a crop such as leafy greens during the winter months. If row covers are used in conjunction with this, sometimes several layers, this increases the ability of the crops to withstand cold weather.
Homemade cold frames are another method of season extension, with or without the addition of row covers. There are plans online and in books for constructing these, often made out of scrap windows. A simple one utilizes a framed garden bed and a stick to keep the hinged glass panel open for venting on a warmer sunny day. A caution though is to be sure you don’t use windows painted with lead paint. If you cover the crops inside of the cold frame with row covers this will increase the protection on cold nights.
Other materials include slitted or solid plastic row covers. The idea behind slitted plastic row covers is that heat buildup on sunny days will be dissipated via slits in the fabric while creating a sort of mini-greenhouse. It allows near 100% light penetration and total visibility of the crop at all times to assess flowering or weeds. I’ve used these in the past but prefer good polypropylene row covers myself.
If you’re interested in trying this, buy a small amount, and try it out on a heat-loving crop such as peppers or eggplant, especially if you’re in the North. Although it’s supposed to provide a few degrees of frost protection, I don’t trust it as much as I do spunbonded row cover. Your mileage may vary though so experiment if you’re adventurous.
I don’t like the idea of solid plastic material being used over hoops as the heat could build up rapidly in the sun, it won’t provide as much frost protection as spunbonded row covers, nor will it allow rain to penetrate. If you use plastic row covers, anchor the edges with soil and not metal staples.
Once you’ve tried using good professional row cover materials though, you won’t want to find yourself scrambling to raid the linen closet anymore of all of the sheets and blankets you own!