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College of Food, Agricultural, and Environmental Sciences


Biomass Crop Makes for Good Nursery Container Potting Mix

February 18, 2010

WOOSTER, Ohio – Switchgrass is proving to be a viable nursery container potting mix, providing the green industry an alternative to the industry standard and potentially opening the doors for biomass production in Ohio.

U.S. Department of Agriculture adjunct scientists with Ohio State University's Ohio Agricultural Research and Development Center have found that switchgrass, with several amendments (peat moss, fetilizers, compost) mixed in, can replace pine bark to support and enhance root growth of short-term production nursery container crops. Such crops include herbaceous perennials and woody shrubs, such as roses.

The study, "Use of Switchgrass as a Nursery Container Substrate," has been published in a recent issue of the journal HortScience. The research was in response to concerns in the green industry of the increase in price and decrease in availability of pine bark – the industry standard substrate for nearly three decades.

"There is a history and comfort among nursery growers in using pine bark, a byproduct of the timber industry, as a container substrate. But with the current economic crisis and increase in energy prices, paper mills and lumber mills are now using that pine bark to fuel their own facilities rather than selling it as a byproduct to nurseries and other horticultural industries. In addition, demand for forest products has decreased, so pine bark is not as readily available like it used to be," said James Altland, a USDA-Agricultural Research Service research horticulturist. "Our goal was to figure out if there was a material out there that can be used as a potting mixture that has a consistent, high quality like pine bark. With agriculture dominating Ohio land, we immediately looked to biomass products as an alternative."

Altland said switchgrass was chosen because of its high biomass potential and the possibility of establishing a production system that can link the farmer to the nursery industry in locally producing and processing a high-value crop.

"Someone once told me that carbon is no longer for free," said Altland. "Finding someplace that will sell organic materials for the nursery industry cheaply is not happening. So instead of relying on a byproduct, why don't we develop a system that both the farmer and nursery grower can benefit from?"

While the infrastructure is not yet in place, Altland envisions a system that allows the nursery industry to contract with a farmer to grow switchgrass and then process it to grind it to the desired potting mixture consistency. Each year the Ohio nursery industry uses approximately 140,000 cubic yards of pine bark. Potentially up to five tons of switchgrass can be produced per acre, producing 50 cubic yards of switchgrass substrate mix per acre. This means that about 2,800 acres would be needed to produce the potting mix the Ohio nursery industry would require each year.

"That's not really a whole lot of acres," said Altland. "So it's definitely feasible." He estimates it would cost the farmer about $5 to $6 per cubic yard to grow switchgrass compared to $4 a cubic yard for corn stover, which is also being reviewed as a potential nursery container substrate.

While switchgrass works, said Altland, it may not be a product that can be grown under all environments. So researchers are looking at other biomass products, such as giant miscanthus. Giant miscanthus, a type of grass, can yield two the three times as much as switchgrass. And technology is opening the doors for farmers in the Midwest to grow it. A new planter has been developed that allows growers to rapidly and efficiently plant rhizomes of the crop, which was a hurdle previously limiting the number of acres planted to giant miscanthus.

The biomass products may sound promising, said Altland, but researchers are hoping that farmers can use what is already available – wheat straw.

"There isn't a big market for wheat straw itself, so farmers may just bale some of it up or till it under," said Altland. "With 800,000 acres of wheat planted this year, we hope that our research proves that wheat straw can also be a viable nursery container substrate."

The research is being funded by the USDA-ARS Floriculture and Nursery Research Initiative.

Candace Pollock
James Altland