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UNCE horticulturist helping find the best compostable plant pot

Posted 7/31/2012

Heidi Kratsch

Heidi Kratsch

Kratsch’s research could usher in a new era of bioplastic containers

Heidi Kratsch likes to grow things — no surprise there, since she’s University of Nevada Cooperative Extension’s statewide horticulture specialist.

But one thing Kratsch doesn’t like about gardening is the overwhelming stack of plastic pots that accumulate after she transplants her young plants into the ground. The petroleum-based plastic pots that most seedlings come in when when you buy them at a retailer don’t decompose and can’t be recycled, so they tend to accumulate.

"By the end of the season, I’ve got pots stacked so high that they threaten to tumble on my head," Kratsch says.

So when researchers at Iowa State University were looking for scientists to help them develop and evaluate biodegradable pots, Kratsch stepped forward right away. The idea is to come up with a pot that you can plant in the ground with the seedling and be assured that it will decompose in time for the plant’s roots to reach into the surrounding soil. Kratsch’s research this summer will show what type of biodegradable pot breaks down best in Nevada’s soil.

Marnie Brennan

Marnie Brennan

Marnie Brennan, the "garden coach" at the Garden Shop Nursery on Mayberry Drive in Reno, is eager to see a good biodegradable pot reach the market. She thinks consumers will welcome a pot they can plant in the ground.

As it is, a lot of her customers ask her what they should do with their leftover black-plastic pots, which are made from recycled plastic and can’t be recycled again. Brennan’s nursery accepts the empty pots when customers are through with them and ships them back to some of their nurseries to be used again.

"I think our customers — particularly our 20- or 30-somethings — would love to have a pot they could plant or throw into the compost," said Brennan, who will work with Kratsch on market research for the biodegradable pots in coming years.

Finding the perfect pot

Kratsch noted that biodegradable pots have been around for more than 30 years since the first ones came on the market made out of pressed peat moss. Biodegradable pots have also been manufactured with coconut fiber, paper, wood fiber, sugar cane and palm fiber. The problem with them is that they haven’t been reliable and tend to wick away water from the root zone if any part of the pot is exposed above ground, Kratsch said.

Bioplastic pots

A new generation of pot that Kratsch is studying is made out of "bioplastics" and is similar to bioplastics used by the food industry for drink cups, food containers and storage bags. These materials are made from sugars or starch and decay readily, but the early versions often haven’t been strong enough to work as plant pots and some leave a plant-harming residue as they degrade in the ground.

Kratsch now is working with pots made from such farming byproducts as corn or soy protein, rice hulls and protein extracted from chicken feathers. One version uses a byproduct of corn ethanol production called zein, a corn protein that is strong and water resistant until it is planted in the ground.

Kratsch’s research began in mid June when she planted six rows of pot fragments in the ground at UNR’s Main Station Farm. Each row contains three samples each of 30 different bioplastic pot formulations, as well as some "control" pots, including the existing petroleum-based pots and some old-style pressed peat moss pots.

Each month, Kratsch and her team harvest a row of pots and weigh them to determine how much decomposition has taken place. Kratsch’s research will show how well the different prototype pots do in Nevada’s non-fertile soils — typical of many areas of the arid West — while similar studies being done in Ohio, Iowa and Illinois will record how well the pots do in wetter climates with better soils.

Bioplastic pots being harvested to determine decomposition.

"The biggest question is whether any of these pots will perform as advertised in Nevada’s soils," Kratsch said. "Our soils are low in organic matter and, therefore, also low in microbes needed to decompose products like these. Adding compost and organic matter can help, but there are no guarantees."

"So far," she said, "the soy- and corn-based pots are "decomposing really fast."

"We’re finding that they fall apart in about a month," Kratsch said. "That’s what the other sites are finding as well."

Pots as fertilizers

Next year, Kratsch and her fellow scientists will study how well seedlings do in various pots. They’ll try to determine if the bioplastic pots do, in fact, aid the growth of the plant by providing nitrogen to the roots as the pots disintegrate.

In the third year of the study, Kratsch will work with Brennan at the Garden Shop Nursery as well as nursery owners at Drycreek Garden Company in Reno and Hungry Mother Organics in Minden to see how well the pots are received by the gardening public. Are customers interested in biodegradable pots? Will they plant seedlings in the pots or will they compost the pots? Will they pay extra for a product that is pot and fertilizer in one?

"It’s really the ultimate recycling," Kratsch said. "With these pots, we’ll be putting back into the earth a product that came from the earth."

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