Is Wood A Viable Media Component?

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Is Wood A Viable Media Component?

Peat moss is an absolute necessity for greenhouse growers. The industry simply couldn’t do without it. But the cost of shipping peat across Canada to southern parts of the United States is forcing Southern growers to look for resources that are capable of supplementing their bread-and-butter growing media component.

One resource to which growers are slowly turning is wood. Wood, by no means, is a peat replacement. Plus, it’s a resource nursery producers have historically relied on more than greenhouse growers.

Still, horticulturists are discovering that wood, when used in the right ratio to peat and for the right crop, is a serviceable growing media component. USDA and university researchers, for example, have grown a wide range of crops–annuals, perennials, tropicals and woody ornamentals–using processed whole pine trees as a growing media component. And the results of this research are enlightening.

“Commercially, I think we could switch to 50 percent wood in our growing media,” says Anthony Witcher, a horticulturist at the USDA Thad Cochran Southern Horticultural Laboratory in Poplarville, Miss. “It could be an even higher ratio, but I think growers would have to address such issues as crop fertilizer and irrigation needs due to the reduced nutrient and water-holding capacity.”

Witcher’s research, under the direction of Jim Spiers, is focused primarily on evaluating substrates composed of processed whole pine trees and pine tree residuals for greenhouse and nursery crop production and propagation. Witcher’s and Spiers’ work is a collaboration with Glenn Fain, an assistant professor in Auburn University’s horticulture department, and includes propagation experiments in cooperation with Eugene Blythe, an assistant research professor at Mississippi State University’s South Mississippi Branch Experiment Station.

Another Alternative: Rice Hulls

Rice hulls, like Riceland’s PBH, are a perlite replacement that produce optimum air-filled pore space, water-holding capacity and drainage in growing media. New this year at Riceland is the procedure by which rice hulls are processed before bagging.

“PBH is a highly processed material to begin with, but we are now screening and checking it on an hourly basis before it’s processed,” says Mark Shepherd, Riceland’s eastern regional sales manager. “It takes us about four hours to pack a load. Every hour we are checking the material for integrity and cleanliness.”

In the next year or two, Riceland plans to commercially introduce a hammermilled material that serves as yet another growing media component. Shepherd says Fafard is one supplier that’s trialed ground whole hulls, added them to mixes and found the ground hulls retain more moisture. A combination of ground and whole hulls, Shepherd says, is capable of being used at a 1-to-1 ratio with peat moss.

Growers who would like to incorporate PBH with a mix can put in special requests with Fafard or Berger Peat Moss.”It’s already available today,” Shepherd says. “If a grower wants to call Fafard and say, ‘I want my 3B mix with PBH,’ Fafard already has that in place.” They will make that mix for the grower. Fafard and Berger both offer PBH mixes. The grower just has to request them.”

“Wood fiber substrates offer the potential of cost savings, and it’s a potentially local product,” Fain says.

Already On Board

USDA and Auburn University actually collaborated on a growing media project incorporating the whole tree substrate at Young’s Plant Farm in

Auburn, Ala. Young’s is fortunate to have a sufficient supply of pine trees on its property, and because peat is being shipped more than 800 miles to the operation, the expense was one the Young family wanted to reconsider.
Ultimately, Young’s purchased the equipment to harvest its own trees, and it invested in a hammermill to grind those trees to the right particle size.

Obviously, then, harvesting trees, processing the wood and incorporating it into growing media is a viable alternative for Top 100 operations like Young’s Plant Farm. But what about smaller operations looking for cost relief?

“If you have a group of nurseries that are close together, there is potential they can form some kind of corporation to produce a growing media product,” Witcher says.

But the most logical way smaller growers could pounce on wood as an alternative growing media option is if it were more commercially available.

“We’re certainly acknowledging the importance of developing innovative growing media,” says Jamie Gibson, director of research and development at Fafard. “We’re quite proud to make available a proprietary wood substrate growing medium. With wood, you’re talking about something that’s very different and unique for our industry. We’re seeing growers have positive experiences with it in our own trialing program, and it’s been interesting to get their takes.”

The Big Picture

Hugh Poole, technical services director for Fafard, agrees the potential of wood to our industry is great, especially when considering transportation costs.

“We recognize that transportation costs are driving things far more than raw material costs,” Poole says. “So we’re looking for sustainable alternatives that are closer to our plants that we can work with.

“We see a lot of opportunities with wood, but we have several other components we’re evaluating as well. The driving force is what raw materials are locally available and sustainable in order to drive down transportation costs. That’s our enemy.”

One concern Poole has about wood and its place as a growing media component is its overall role in our industry. More growers, after all, are burning wood to heat their greenhouses than producing their plants in it.

“I hope there’s not this big issue with getting subsidies for using wood for burners and boilers,” Poole says. “That certainly skews all the financials and cost factors dramatically. We find bark and wood fiber to be very good aggregates in our mixes, and I think it’s sustainable. So as long as it doesn’t get outrageously priced, we can be competitive procuring it and using it in our mixes.”

As a researcher, Witcher has witnessed wood’s capability as a growing media component. But before growers jump on the bandwagon, he believes commercial suppliers must promote it.

“I think there are a lot of growers willing to try it,” Witcher says, “especially if it’s a product that would bring substrate costs down and they wouldn’t have to significantly modify cultural practices like irrigation and fertilization.”

Kevin Yanik is the former managing editor of Greenhouse Grower.
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