This story was originally published in June 2020.
Weeding is one of the most annoying parts of gardening, but it is necessary if you want a productive harvest. Home gardeners and professionals alike are always looking for new solutions for weeding woes, from mixing it up with mulches to taking a flamethrower to the pesky plants.
One preventative strategy could rid you of your weed issues forever, as long as you employ a bit of advanced planning.
Sonja Birthisel, postdoctoral research Associate at the University of Maine, has conducted research on weeding strategies that involve covering plots before planting with reusable plastic tarps for about a week. The technique, aptly known as “tarping,” is gaining popularity in the gardening world, especially for small farms looking to control weeds effectively and efficiently.
Here’s how it works: prepare a smooth, flat garden bed, and moisten thoroughly (setting up right after a rainy day is ideal). Before you plant your crops in your garden plot that is otherwise prepared for spring planting, secure an opaque black or blue tarp (these darker colors are not only more common for store bought tarps, but they also conduct heat better) tightly over the soil.
“You can do this either by tilling in the spring and applying the tarp, or applying the tarp on residue from last year,” Birthisel said. “Some people find that this strategy can help them do a no till approach to gardening.”
Birthisel said to make sure that the tarp is secured tightly around the edges with bricks, sandbags or weights of some sort, distributed every couple of feet around the perimeter of the tarp to make sure no light can enter.
“What we want to do is cause fatal germination of seedlings in that environment,” she explained. “When you’re tarping, you’re helping to deplete the seed bank, the store of weed seeds in your soil.”
The process will create a “stale seedbed,” where the weed seeds hiding underneath your soil are killed with minimal soil disturbance — and, for that matter, labor.
Leave the tarp for seven to ten days before removing it and sow your crops or seeds directly into the plot. Do your best not to disturb the soil around where you’re planting.
“After tarping, you don’t want to disturb the soil afterwards because you’ll bring up new weed seeds,” Birthisel said.
This strategy is similar to another weed management strategy known as solarization, which uses clear plastic, often when they are no longer needed from an old greenhouse or hoop house, instead of an opaque tarp.
Birthisel’s research shows that solarization may have a short-term negative impact on the soil’s biological activity. However, solarization can be more effective for suppressing weeds, especially with shorter treatment durations, so you might look into a clear plastic tarp if you’re eager to plant. However, Birthisel said that solarization can be finicky — and, worse, can backfire.
“It’s really essential to tightly secure the edges by burying them, [or else the weeds] might grow extra well,” Birthisel said. “I recommend it with caution.”
