June 19, 2018
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Floating row covers foil herbivores in the vegetable garden

Reeser Manley | BDN
Reeser Manley | BDN
Potatoes in the Eastport Schoolyard Garden, after their first hilling, going back under a floating row cover.
By Reeser Manley

Every Sunday afternoon, I climb to the top floor of Lynne’s old playhouse to take a sweeping photograph of the vegetable garden — a useful way of recording change over time. The most striking change in the latest photo is the sudden appearance of a white blanket covering the potato bed, a floating row cover held in place with heavy stones.

What are floating row covers?

Floating row covers are a chemical-free way of denying plant-eating insects (herbivores), such as the Colorado potato beetle, access to your vegetable crops. They also keep out squash bugs, cucumber beetles and squash vine borers from squash, cucumbers, and pumpkins. They keep cabbageworms and root maggots from finding your broccoli and they will foil bean beetles, corn earworms, whiteflies, grasshoppers, spinach leaf miners, aphids and leafhoppers. Most garden row covers are a polypropylene fabric of varying weights. For insect control, we prefer a lightweight row cover (0.45 ounces per square yard) that retains very little heat in the soil while transmitting 95 percent of available light. Water from rain or irrigation easily passes through the fabric.

Available in rolls of varying length from garden stores and online, standard row cover widths range from 5½ to 8 feet, and wider is always better. Be sure to buy a width that will accommodate the upward growth of the plants.

Installed with plenty of slack between bed edges, our potato bed row cover literally floats on top of the growing plants, providing a millimeter of hindrance to potato beetles. And because producing potatoes does not involve pollinating insects, the row cover will remain over the potato bed throughout the summer.

How to use floating row covers

For leaf and root crops, row covers can be kept on throughout the growing season. For crops that require pollination by insects for fruit production, row covers must be removed during flowering.

Some crops, such as tomatoes, peppers and others with fragile growing tips, do better if the row cover is supported with hoops. Many gardeners use hoops made from 9-gauge wire cut into 6-foot-long pieces. The ends of the hoops are pushed into the ground. In raised beds framed with timbers, small holes can be drilled in the top timber to support the hoops. Other options for hoops include inexpensive plastic pipe, the ends pushed into the soil or slipped over rebar stakes. Rebar stakes with plastic end caps work well for supporting row covers over tall plants.

Row covers can be used for two or more seasons if properly used and stored. Small rips in the fabric can be closed with staples or clothespins and, at the end of the growing season, much of the soil can be removed by hanging the fabric on the line and rinsing it with a gentle spray from the hose. Once dry, fold the fabric for storage indoors.

When floating row covers work (and when they don’t)

Using floating row covers successfully requires knowledge of how insects overwinter.

For example, some herbivores, like the Colorado potato beetle, spend the winter as adults in the soil near the plants on which they fed as larvae. If potatoes are planted in the same bed the following spring and the bed is covered with fabric, these adults will emerge to find their favorite food handy beneath a cover that protects them from their natural enemies. Other herbivores that overwinter near last year’s plant host include the onion maggot, corn rootworm and flea beetle (affects many vegetable seedlings). Clearly, crop rotation must be used along with row covers to foil these herbivores.

Some herbivores, such as slugs, cutworms, millipedes and sowbugs overwinter in scattered locations around the garden. These insects have the greatest potential for causing plant damage under row covers, since they could emerge anywhere in the garden. Frequent inspection is key. If noticeable populations of these herbivores are found, the row cover should be removed to allow beneficial insects access to their prey.

Floating row covers should be used only to prevent establishment of an herbivore capable of serious damage, such as the Colorado potato beetle, but they should not be used at the expense of building strong populations of beneficial insects. Cover everything and the beneficials will disappear, a recipe for disaster.

We grew potatoes for the first time last year and, using the row cover from the start, never saw the first beetle. This year we rotated the potato crop to another bed and again installed the row cover just as the first leaves were emerging from the soil. This combination of crop rotation and floating row cover should keep our garden potato beetle free.


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