WholeTree Provides A Sustainable Substrate
Looking to take some of the variables out its growing media, Young’s Plant Farm started to produce one of its potting mix components from whole pine trees. Find out how the WholeTree substrate provides growing media flexibility.
November 13, 2012
Growers hate surprises, especially when it comes to costs. So when the price of fuel or other supplies start to increase, most growers look for ways to hold down costs without sacrificing product quality. This is especially important at Young’s Plant Farm in Auburn, Ala., where the company motto is, “Grow the best plants, always.”
A Media Component Alternative
Researchers at Auburn University have been looking at alternative components in nursery growing media for several years. In 2004, USDA scientist Glenn Fain and then-Auburn Department of Horticulture chair Charles Gilliam discussed the concerns nursery growers voiced regarding pine bark supplies. It was during this meeting that Gilliam mentioned the idea of harvesting and grinding young, whole pine trees to make a substrate, a process referred to as WholeTree.
Fain began research on the WholeTree substrate along with other alternative media components in 2004. The research was done in collaboration with Gilliam and Auburn University Horticulture Professor Jeff Sibley. At the time, the USDA Thad Cochran Southern Horticultural Research Laboratory in Poplarville, Miss., and the university entered into a formal agreement to work on alternative substrates. Fain, who received his Ph.D. from Auburn and returned to the university in July 2007 as a horticulture professor, continues to work with WholeTree and other substrates.
Fain, Gilliam and Sibley have also directed numerous graduate students working on various aspects of alternative substrates. In the past six years they have published over 20 peer-reviewed scientific papers on their research and have presented results at numerous scientific and industry conferences.
Hurricane Changes Crop Focus
“Initially we were working on substrates and nursery crops,” Fain says. “We weren’t looking for a substrate for greenhouse crops. I grew up working in a wholesale and retail nursery, so my background and research area focused on nursery crops.”
All that changed when Hurricane Katrina hit the Gulf Coast in August 2005.
“The first time we cut down a whole tree and ground it up to make a substrate was in the spring prior to Hurricane Katrina,” Fain says. “We initially chose the Southern pine (Pinus taeda) because of its availability throughout the South. Our initial goal was to find a substrate for nursery crops that was not a byproduct of another industry. We were primarily trying to find an alternative to pine bark, which is a byproduct of the pulp and lumber industries. Pine was a logical choice since it is widely available and easy to grow.”
When Hurricane Katrina came through Mississippi, it wiped out all of Fain’s nursery crop trials. In an effort to get his research back up and running Fain chose to work with greenhouse crops.
“Where a nursery crop would take six months to a year to get any results, trials with greenhouse crops could be finished in 30 to 60 days,” he says. “I primarily studied bedding plants and a few perennials because they are also relatively quick crops.”
Researching Potential Substrates
After seeing positive results with the WholeTree substrate, Fain and his colleagues presented a poster on the research at the American Society for Horticultural Science conference in February 2006. Gene Young, who founded Young’s Plant Farm, heard about the research from long-time friend and former Auburn Department of Horticulture Head Ron Shumack. Young contacted Gilliam and Fain about the potential of using the substrate at his production facilities in Auburn.
“The Youngs saw what we were doing and wanted to get on board to help with the research,” Fain says. “The USDA formally entered into an agreement with the company to do the research, which was conducted at both its greenhouses and at the USDA lab. Auburn University also was involved with the studies. I returned to Auburn in July 2007 and continued working with the WholeTree substrate as well as other biomass products as potential substrate components.”
WholeTree Provides Flexibility
Young’s Plant Farm President and CEO Greg Young says the company has been trialing WholeTree substrate for more than six years and has been using it on regular basis for about three years. Young’s produces flowering annuals, garden mums, foliage plants and flowering pot plants, including poinsettias, cyclamen and kalanchoes. Most of the plants are sold to mass merchandisers.
The potting mix used at Young’s consists primarily of peat moss, perlite, vermiculite and WholeTree substrate. For some crops, pine bark is added. WholeTree is not used in the company’s plug mix.
“We have a variation of mixes that we use,” Young says. “The WholeTree substrate is normally used in 95 to 99 percent of our production.”
Young says on average WholeTree accounts for 20 to 25 percent by volume of the growing mixes. He said that percentage can vary depending on the crop and grower preference as to how much of the substrate is added to a mix.
“WholeTree works well as a supplement or alternative component in our growing mixes,” he says. “It helps with drainage. It helps reduce the amount of perlite we add in. It helps reduce the amount of peat that we have to buy. It is a replenishable resource that is locally grown rather than coming out of peat bogs in Canada and Europe. It definitely gives us some flexibility.”
Harvest, Haul, Chip And Mill
When Young’s initially began trialing the WholeTree substrate, trees were brought in from other locations in and outside the state, including Georgia and Mississippi. Young’s is now harvesting all of the pine trees it processes off its property.
“We probably don’t use more than 25 to 30 acres of land in a year. We are cutting 12- to 15-year old pine trees. We have plenty of timberland on which we can cut and replant the trees to meet our needs,” Young says.
Once the trees are cut, they are carried to the dock for processing.
“We are more careful with the hauling of the trees than most logging companies that harvest trees for pulp or lumber,” he says. “We want the trees to be as clean as possible. We don’t drag the trees along the forest floor to avoid picking up weed seeds or snagging other plants.”
Young’s has purchased all of the equipment for harvesting, hauling, chipping and milling the trees, as well as the equipment it uses to produce all of its growing mixes. The only part of the pine tree that is not used to make the WholeTree substrate is the roots. The needles, bark, trunk and pine cones are all processed and chipped. The chips, which are stored under a covered structure, are mixed a couple of times to help reduce their moisture content.
Then they are milled into 61-cubic-foot, UV-resistant, 6-ounce nylon tote bags. The bags, some of which are stored outside, have been used for three years and are re-used as many as 10 times. The substrate is cured for several days to a couple of weeks. During the curing process, the temperature in the bags rises to a range of 140˚F to 160˚F before stabilizing and dropping to the ambient temperature. WholeTree, which has been stored for up to two years, has been used to grow crops without any significant changes in its properties or performance, Young says.
Producing WholeTree Year-Round
“The substrate is lot easier to produce in the spring, summer and early fall,” Young says. “In the late fall and winter, the trees start to produce sap and that causes the milling process to use more energy. The speed of the process is reduced by 25 to 30 percent because the trees have so much more moisture compared to other times of the year.”
Young’s processed about 50 trailer loads of wood chips in 2011. The company usually chips about one trailer load per day, which produces 50 to 60 tote bags of substrate.
“We chip enough substrate to meet our needs for the entire year within a 45- to 50-day period,” Young says. “We don’t chip all the trees at one time. We do it at different times of the year.”
On the few occasions that the company has come up short on its supply of the substrate, it is usually an issue of logistics. Young says that during the periods when the equipment is running and the trees are being processed, there is enough substrate for the crops that need it.
“Periodically we may not put the substrate into the mix for a certain crop because we may have not tried growing that crop in it before,” he says.
Substrate Requires Subtle Changes
Fain says growers who use wood fiber substrates like WholeTree might have to make some subtle changes to their production practices depending on percentages used.
“These include primarily changes to nutrition and water management,” he says. “These substrates don’t have a lot of cation exchange capacity or much buffering capacity. That is one of the positive characteristics of peat, which has a high cation exchange capacity and more buffering capacity.”
According to Fain, wood fiber substrates can be affected more quickly by nutrient sources. For example, application of a fertilizer high in nitrate nitrogen would raise the medium pH, and one high in ammoniacal nitrogen would lower the pH. This change also occurs in peat-based media, but it is much more subtle. This has not been an issue in studies with a growing mix consisting of 40 percent or less WholeTree and peat.
“The negative with the wood fiber products is the growing medium pH can get out of line more quickly,” Fain says. “The positive is that it is easier to bring the pH back to where it should be. This is why we advise growers not to make the wood fiber product the major component of their mixes because of concern with trying to manage the pH.”
All of the WholeTree substrate Young’s produces is used for its own production. The company hasn’t tried selling any of the substrate to other growers because of its weight limitations.
“The substrate would have to go through a drying process and there would be a fuel cost involved with removing the moisture,” Young says. “Looking at a shipping range of 100 to 200 miles, we would have to do the calculations to see if it was worth drying and compressing the substrate for shipping. There are a lot of options for drying and packaging.”
In addition to providing the company some flexibility with the components it can use in its potting mixes, WholeTree has helped the company reduce its peat costs.
“This becomes even more important when fuel starts to approach $4 a gallon,” Young says. “With peat coming out of Canada, half of the cost is peat and the other half is freight.”