Mulch ado about garden plastics
by Eric Sorensen | © Washington State University
In 2001, Carol Miles certified WSU’s first piece of organic land, a three-acre parcel at the WSU Vancouver Research and Extension Unit. It was a landmark moment, leading the way for organically managed land at all of WSU’s research facilities.
But one thing kept nagging her: the plastic.
In the absence of conventional herbicides, weed control was her number one issue, and laying down a layer of plastic took care of the problem handily. But it’s nonrenewable and not recycled.
If it’s going to be used in an organic production system, reasoned Miles, now a vegetable horticulturist at the WSU Mount Vernon Northwest Research and Extension Center, it really should be renewable or recyclable.
The problem extends beyond the occasional three-acre parcel as well. With more than half a million acres of black plastic spread across American farmland, it starts to add up, turning into more than 100,000 tons of trash that costs millions of dollars to dispose of.
As home gardeners might imagine, the solution should be as simple and mundane as a cardboard-lined path. Surely there must be some sort of paper product that could fight weeds as well as plastic, then mulch away like the paper coffee filters that disappear so routinely in the compost pile.
It turns out it is not so easy to align the needs of farmers, consumers, regulators, vegetables, soil, mulch-degrading microorganisms, and the range of farming conditions across America. But Miles and a host of other researchers are managing to make some progress with a blend of horticulture, polymer chemistry, economics, plant pathology, soil microbiology, sociology, and a plant-based fabric.
In 2003, Miles started five years of test plots with various crops. She tried Garden Bio-Film, a starch-based product from Europe. She used a film called Envirocare. She tried kraft paper, so named for the nineteenth-century process to convert pulp. She used Longview Fibre raisin paper, which is ordinarily used to sun-dry grapes.
They all had trade-offs.
Plastic remained the most durable, while Garden Bio-Film was expensive and too biodegradable, breaking down before summer’s end. Envirocare wasn’t biodegradable enough, even in a postharvest compost pile, nor is it approved for organic ground.
Weeds frequently grew under paper, pushing it up and causing it to tear. As soil microbes start breaking it down at the edges, it is easily lifted by the wind. Once it covers less than half the ground, it is basically useless for weed control.
Paper also weighs a lot.
“The heaviness comes into play in a lot of different ways,” says Miles. “You have to ship it, and a roll weighs several times more than a roll of plastic. A 500-foot roll of paper weighs as much as a 5,000-foot roll of plastic in some cases.”
When Miles moved to Mount Vernon in 2007, her mulch work caught the eye of Debra Inglis, a WSU plant pathologist. The two and a team of other researchers secured $2 million under the USDA’s Specialty Crop Research Initiative, plus a matching $2 million. The effort included researchers in Texas and Tennessee, stretching the range of conditions and crops in which biodegradable mulch might be used.
Through Karen Leonas, professor and chair of the Department of Apparel, Merchandising, Design, and Textiles, they also started working with fabric made from plant-based polylactic acid.
The first prototype didn’t block weeds, probably because it was too lightly colored.
“It was a greenhouse,” says Miles.
Last year, they used a darker version that worked better at holding down weeds.
But the researchers are still struggling with making the mulches execute a tricky natural timing play. They want them to hold up during the growing season, then disappear over the winter so there is clear planting ground in the spring. But materials break down best in the summer, when heat, light, and microorganisms are most abundant.
“Biodegradation is microbially driven,” says Miles. “There’s very little microbial activity in the wintertime. Therefore, it’s very unlikely biodegradation is going to happen in that six-month time frame.”
Their Tennessee colleagues are looking at a catalyst that might be applied to a mulch late in the season. The aim now is to speed along its degradation just when a farmer will want it to disappear.
Comments are temporarily unavailable while we perform some maintenance to reduce spam messages. If you have comments about this article, please send them to us by email: email@example.com