June 25, 2019
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.
Tarping technique
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.