By Susan Harlow
Vermont farmers Danielle Allen and Ben Carr are doubling their usage of tarps this season.
Covering vegetable beds with black or white silage plastic has many benefits. Deprived of light, weed seedlings die. Also, the beds can be prepared weeks in advance of planting without more tractor cultivation, cutting down on compaction.
Moisture is preserved, and soil fertility has improved with less nutrient loss, Allen says. Tarps also help suppress disease.
But there are challenges, too. Moving the heavy tarps and the sandbags that hold them down requires a good deal of labor. Managing weeds along the tarp edges, a hard place to cultivate or hoe, is difficult.
Allen and Carr’s Root Five Farm in Fairlee lies adjacent to the Connecticut River. They bought the 38-acre farm in 2013 after the land they were farming in Burlington’s Intervale was severely damaged by Hurricane Irene in 2011.
They grow more than 100 varieties of vegetables, flowers and herbs for their 200-member Community Supported Agriculture venture. They sell produce at the Norwich Farmers Market and at a weekly one-day market they set up by the local grocery store. They also market to several local cooperatives and restaurants.
For tarping, Allen and Carr prioritize beds for direct-seeded, successional crops such as lettuce mix, arugula and herbs. They try to target hard-to-control weeds such as goosefoot.
They start by covering 30 of their 100-foot beds, peeling back the tarp on four beds each week. They have 356 100-foot beds and 206 200-foot beds.
It takes at least four people to move the heavy tarps and fold them back, especially when it’s rained. But the water helps to hold down the tarps closer to the soil, and it’s that ground contact that seems to suppress weeds.
“Ideally the bed is under plastic for three weeks, but the longer the better,” Allen says. “We don’t field-cultivate after the tarp is off because that stirs up weed seeds. It’s really important to think of it as a stale-seed method.”
Allen and Carr are experimenting with using tarps to overwinter beds where it’s too late to plant a cover crop after harvest. Tarps also help reduce erosion and wind loss, and they’ve found that it improves soil quality, too.
IMPROVED SOILS: Danielle Allen, co-owner of Root Five Farm, says soil structure has improved in areas where tarps are being used.
“It's our goal to leave no beds bare over the winter,” Allen says. “When we tarp an area over the winter, we pull [the tarp] off in the spring, prepare the beds (chisel plow, spread amendments, bed-form) and either plant, re-tarp or cover crop, depending on the crop plan for that area.”
If a cover crop has overwintered, they’ll plow under in spring, disk and field cultivate, amend the soil, irrigate if needed, and then cover it with black plastic.
Their first use of tarps was to break down cover crops more quickly. For example, they might plant oats and peas in the spring, then mow and plow it under. The bed is covered immediately with tarps, then removed after three weeks or so to direct-seed carrots or other fall crops. They use buckwheat as a cover crop in summer, and rye and vetch as a fall cover crop.
Ideal for small farms
They purchase the plastic from a local dairy supply store.
“It’s really tough and we get a couple of years out of them,” she says.
The tarps cost $162 each for a 50-foot-by-100-foot tarp.
“So far we've gotten three years use out of them,” Allen says. “They're still in good shape, so we anticipate getting several more years out of them. Let’s say we get six years out of them, that would be only $27 per year. The cost of the tarps is definitely offset by the money we save in cultivation and hand weeding.”
“Tarping is most applicable for farms our size or smaller,” she adds.
So, what’s Allen’s advice for someone who wants to use tarps?
START SLOW: Allen owns Root Five Farm with her husband, Ben Carr. Her advice to farmers wanting to use tarps is to try one or two tarps to “get a feel for it.” That way you’ll know if tarps are good for your farm or not.
“Start with one or two to get a feel for it, and have enough people or cut the tarps to a size that’s manageable,” she says. “Wrestling those things around is the biggest problem.”
You’ll also need a way to transport sandbags. They keep the sandbags in wooden bins, which they move around the farm using a tractor.
This is the third season Allen and Carr have used tarps.
“So far, the beds have been beautiful,” she says. “It’s kind of set it and forget it.”
The Vermont Vegetable and Berry Growers Association held a conference on mulching and tarps in February. There’s a lot interest in the technique, according to Vern Grubinger, vegetable and berry specialist for University of Vermont Extension.
“Dozens, if not hundreds, of farms are experimenting with tarps on a small scale,” he says.
The proceedings are available online.
Allen and Carr first learned about tarping from Quebec farmer Jean Martin Fortier’s book "The Market Gardener.”
Harlow writes from Vermont.