Plastic Mulch is Problematic—and Everywhere. Can We Do Better?

In Washington’s Skagit Valley, the beginning of summer is largely marked by the first ripe, red strawberry. Just off of State Route 20 headed west out of Burlington sits the Skagit Valley location of Viva Farms. Viva Farms is a nonprofit that helps new and limited-resource farmers with access to land, equipment and more, and this site is home to 18 incubator farms and a half-acre student farm. Sales and education manager Katherine Myrvold teaches students in the Practicum in Sustainable Agriculture course how to grow many things here, including two beds of strawberries.

Strawberries are one of many crops that often use plastic mulch during their growing season. Mulching is the process of covering the earth around a plant with something to help it grow. Myrvold says that for the strawberries at Viva Farms, plastic mulch—long, thin sheets of polyethylene—serves two main purposes.

“It adds heat to the soil, which is really beneficial for a heat-loving crop like strawberries. And it also helps with weed suppression, which is always a challenge in organic production.”

But there is a critical downside. There are no consistently accessible mechanisms for sustainably disposing of plastic mulch film at the end of its life. What’s more, research shows that renegade pieces of this plastic can break down into the soil and waterways as microplastics—pieces of plastic less than five millimeters long that present serious health and ecosystem concerns. 

“We always talk about this on the student farm—it’s kind of like the dirty secret of organic agriculture and agriculture in general, is just the amount of waste—the amount of single-use plastic,” says Myrvold. “So, that’s something that we’re very open to finding an alternative to.”

But the current alternatives also have drawbacks. Myrvold says they tried using paper mulch one year, and it tore too easily, wasn’t flexible enough and large swaths of it blew away in the wind.

“It didn’t get the job done at that time,” says Myrvold. 

A new $8-million USDA grant will allow researchers from Washington State University (WSU) to investigate end-of-life recycling solutions for plastic mulch, as well as effective biodegradable mulch options. Researchers across several institutions and industry partners, such as Natureripe and Driscoll’s, will participate, with contributors spanning both coasts. Although many crops use plastic mulch film, this project will focus on a fruit that uses it extensively: the strawberry.

Strawberries from Viva Farms. (Photography by Marcus Badgley.)

The ubiquity of plastic

The use of plastic in agriculture, known as “plasticulture,” is expansive. The United States agriculture sector uses one billion pounds of plastic mulch every year. When it comes to disposal, the vast majority of this film gets taken to the landfill or is buried or incinerated.

When the use of plastic mulch began in the 1950s, it proved to be immensely helpful to growers. The benefits include trapping heat for faster growth, retaining fertilizer and suppressing weeds. It has also proven to be the most economical option for people growing on a commercial scale. 

Plastic mulch is made out of polyethylene, or PE. PE is recyclable, but most plastic mulch film is not recycled because of a few key hurdles. “There’s quite a few things against you,” says Karl Englund, a research professor in WSU’s Civil and Environmental Engineering Department, who is leading the recycling component of WSU’s grant research.

Recycling plastic mulch is not as easy as putting your household recycling in a blue bin. 

Plastic mulch film spends its life in the dirt, and contamination is a real obstacle. Recycling is generally only possible if contaminants make up less than 5 percent of the weight of plastic mulch. But by the end of the growing season, the weight of plastic mulch can increase by as much as 80 percent—all directly due to dirt and organic matter.

Tractor laying plastic mulch ahead of the growing season. (Photography by Jazmine Mejia-Muñoz.)

Moreover, consistent industry pathways for recycling plastic mulch don’t exist yet.

“If there’s no avenue for it to go, then who cares if you clean it?” says Englund. “You build an industry that’s out there that can handle this or at least a group that can say ‘I’ll take this but you got to clean it,’ I think you’ll start to see more and more people starting to clean it. That’s the hope.”

Englund and his team will investigate three different avenues for recycling plastic mulch lifted from strawberry fields: through pyrolysis, for use in road asphalt and as potential added material to deck boards. They’ll use mulch from strawberry fields at different partner sites across the US in Florida, California, Nebraska and Washington and at different levels of cleanliness. Strawberries are an ideal crop to focus on for this research because they’re a popular thing to grow across the country, spanning various soil systems, climates and growing conditions.

But the conversation about how to deal with end-of-life materials needs to start in their initial design, says Englund.

“It’s a quagmire, the position we put ourselves into with these specialty polymers,” says Englund. “[There’s] a lot of design that goes into them and not a design for deconstruction. We have to start designing this stuff better.”

In the fields

The bulk of US strawberries are grown in California—more than 40,000 acres this year. Plastic mulch used for strawberries and other crops has become a problem, however, as plastic pollution can infiltrate waterways.

“There’s a lot of agricultural fields right next to the coast. And so we try to work really closely with ag stakeholders to look at preventative strategies that can help reduce the amount of plastic that can escape out into the ocean,” says Jazmine Mejia-Muñoz, water quality program manager at the California Marine Sanctuary Foundation (CMSF), on detail for NOAA’s Monterey Bay National Marine Sanctuary. By working with researchers and major berry producers in the area, the organizations are attempting to break the link between agricultural plastic use and plastic marine debris.  

Microplastic pollution is a global problem. Although it is difficult to estimate the true extent of the problem, it is thought that there are between 50 trillion and 75 trillion pieces of plastic or microplastic in the ocean. While mulch is far from being the only contributor to this issue, agricultural plastics are certainly a factor. Mulch that breaks down over time could be part of the solution, although a main obstacle associated with the soil-biodegradable plastic mulch currently on the market is that it doesn’t behave consistently across different climates and field conditions. CMSF is collaborating with the WSU team to run trials for biodegradable mulch in strawberry fields. It’s also working with California Sea Grant to investigate new technology to remove contamination from the plastic film without creating wastewater, which would aid in efforts to recycle the material.

Strawberries grown through soil-biodegradable mulch in California’s Central Coast. (Photography by Jazmine Mejia-Muñoz.)

The future of mulch, says Mejia-Muñoz, likely won’t align with just new plastic recycling strategies or biodegradable mulch. It’s going to depend on a combination of different strategies to create a path forward that works for different farm systems with different needs. It’s not only about finding new pathways that work—they also have to be efficient and scalable. 

“In order for the technology to be implemented, it has to be viable, and it has to make sense with the system and the economics around it,” says Mejia-Muñoz.

Should growers just be ditching plastic completely? It’s not nearly that simple, says Mejia-Muñoz.

“Growers here are responsible for meeting food demand, and they feed the world,” says Mejia-Muñoz. “And in order to meet this demand, they rely on really effective technology.”

Beyond plastic

There are several alternatives to plastic mulch—but none can totally fill plastic’s shoes just yet.

Soil-biodegradable plastic mulch film is already on the market, but there are notable obstacles. It degrades inconsistently across varying field conditions and cannot be used for organic farming if it is not 100 percent bio-based, which is required in order to be used in certified organic operations in the US. 

Last year, trials began at WSU and North Dakota State University to determine the most effective formula of hydromulch, a material made of paper, water and tackifier. Hydromulch could contribute to a closed-loop system in agriculture, if the boxes used to transport produce could then become the paper needed to make the hydromulch.

Box of freshly-picked strawberries from Viva Farms. (Photography by Katherine Myrvold.)

Katherine Myrvold of Viva Farms says that despite its less than satisfactory experience with paper mulch in the past, Viva Farms would be open to new techniques or tools. She’d really like whatever the alternative is to add heat to the soil—in the Pacific Northwest climate, the heat boost really makes a difference.

“We would love to try it again, if there’s a newer variety that would last better through the season,” she says.

Myrvold thinks others would be open to it, too.

“I know that there are a lot of people who are working in organic agriculture for all kinds of values-related reasons,” says Myrvold. “It seems like it would be a natural fit to extend that into making an effort to recycle the more wasteful components of what you use on your farm.”