I PLAN TO GROW Crucifers and Cucurbits under cover this year, and the rampaging local woodchuck is the least of the reason why. But I wanted to get the details right from the sometimes-overwhelming catalog choices—the appropriate weight of fabric, and the gear to support the row cover and hold it in place, among other tips—so I called Paul Gallione of Johnny’s Selected Seeds in Maine for some advice.
On the Podcast: Under-Cover Growing
I COVERED under-cover growing on the latest podcast I do each week with Robin Hood Radio, the nation’s smallest NPR affiliate and just down the road apiece from me in Sharon, Connecticut. Stream it now (or find it on iTunes (the April 9 show) and subscribe free).
Gallione, in his position as Technical Services Technician in the research department at Johnny’s Selected Seeds in Maine, is used to answering gardeners’ questions. I started at the beginning with mine: Why grow crops under cover, anyhow?
There are two basic uses for fabric row covers, Paul explained:
- To modify temperature (for heat retention or frost protection, most early and late in the season with heavyweight fabrics);
- As a barrier to keep out insects, crows, and chipmunks, to name a few common troublemakers.
- (Note: You can also create some shade, perhaps for summer salads—though usually with a different type of fabric—but Paul’s and my conversation was about the first two situations.)
Tackling Flea Beetles on Crucifers
TO HELP THWART flea beetles on cruciferous plants like broccoli, cabbage, cauliflower and such, Paul uses fabrics to keep them out. A note: If you had a flea beetle infestation last year, a new generation can hatch from the soil, so don’t plant the same thing in the same spot and expect the cover to solve things. Rotate your planting space!
On direct-seeded crops like arugula (top photo), he says, “I lay the fabric right over the top immediately after sowing—allowing a little play, but not so loose as it will hit the emerging plants.” Other cruciferous relatives of arugula, like radishes and mustard, would benefit similarly from this type of protection strategy.
With Crucifers, the fabric stays in place from four to six weeks. To have complete control, the material can have no holes, and its edges must be buried in the soil (trench alongside the row on both sides with a hoe, then bury the fabric in the trench, using the soil to weight it down–the video below shows how). Or it can be pinned down with ground pins or sandbags for 100 percent coverage. (Rain or sprinkler water permeates.)
Another trick: Paul also uses fabric to protect his corn from hungry, seed-stealing crows (as I do with my peas right after planting, to fight off the chipmunks), leaving the fabric in place for about two weeks.
A lightweight fabric, such as Agribon 15 (called “insect barrier”) or Agribon 19, would be ideal for these uses. The video below explains the use of other weights of fabric, up to heavy “earth blanket”-like frost protectors. An 83-inch width is ample for covering four-foot-wide beds on top of hoop supports; wider fabrics can be cut for custom uses. This pdf compares fabric types and their uses.
Keeping Cucumber Beetles Out
CUCUMBER RELATIVES—or Cucurbits, including melons, cukes, pumpkins and squash—are especially vulnerable to the striped cucumber beetle, which spreads deadly bacterial wilt as it chews foliage. But these plants are less tolerant about having fabric touching their growing points, so some form of support is required to elevate the material, Paul says. Wire hoops (perhaps made from #9 coiled wire) or other supports, such as bent pvc piping or electrical conduit, are among the popular choices.
You can shop for pre-formed hoops or make your own; Johnny’s even sells a tool for bending conduit (seen in the video below, and thoroughly explained in this 12-page illustrated pdf about creating them and growing under cover).
A Cozy Start (and Finish) for Peppers
SOME CROPS need more help with staying warm than with insect pests. Peppers, for instance, might benefit from some extra warmth at both ends of the growing season.
Gallione preps his raised beds with black plastic mulch to warm the soil for these heat-loving plants, then covers the seedlings with light-to medium-weight fabric “to get them off to a good start.” Peppers aren’t sturdy enough to have fabric laid right on top of them, he explains; use the wire hoops or other supports, such as bent pvc piping or electrical conduit, as with the Cucurbits, with this exception:
“If I direct seed the Cucurbits,” Paul says, “I lay the fabric right over the bed—but I wouldn’t do that with tender transplants.” He removes the fabric once they grow up enough and need the room, and the plants are far enough along to be past major beetle vulnerability.
Besides, the flowering pumpkins, squash and cucumbers need insects to get to them for pollination—as do the peppers.
“Once I see blossoms, the covers come off,” says Paul—though with the peppers he may cover them again late in the year. He therefore leaves the supports in place. What you’re creating with hoop-style supports is essentially the architecture of a “low tunnel,” and the framework can support a number of materials, Paul says—“from plastic to lightweight or heavier row cover to shade cloth [below] to bird netting.” Not only is the framework versatile, but it can also be moved to other beds of the same width in subsequent seasons.
Other Row-Cover Tips
ROW COVERS AREN’T a “set it and forget it” tool that let the gardener off the hook. “There’s no substitute for human observation,” says Paul. “You have to be aware—especially as the season heats up.” Always ask yourself:
- Is it hot out, or has it been dry for a period? Rain (or sprinkler spray) permeates the fabric, but remember, so does up to 90 percent of sunlight: It’s a little warmer in there; plants may get thirstier.
- What crop is it, and what stage of development is it at?
- Does it need your attention–to have the fabric vented (below, mine with clothespins added as an extra “clip” to hold the fabric open) to have supplemental water, etc.?
- When pinning them down, use the same holes each time. (The large red Re-Pin brand ground pins that Johnny’s sells may make this task easier.)
- Two people are better than one for rolling out (and rolling back up) fabrics.
- Save the roll itself that the material comes on–to use to store fabric again.
What about all that used fabric that’s no longer in good enough shape to use as a cover again? I hate to throw it away–which has always been one of my issues with row covers: all that waste. Paul had a suggestion:
“I use it to line recycled bulb crates to force Belgian endive,” he said….which got me thinking: It would likewise help turn tag-sale baskets and other not-quite-soil-ready containers into planters. Waste not, want not.