With almost everything in shorter supply or higher in price these days, looking into ways to extend what you have, or even changing up your usual modus operandi, may be the way to go. To help guide your way, W. Garrett Owen, Ph.D., from Ohio State presented “Extending Your Peat and Exploring Alternative Substrate Components” at the most recent Great Lakes Expo.
Owen explained that substrates provide four services: plant support, nutrient retention, aeration and water retention. Recent research has focused on peat conservation, due to sustainability concerns, irrigation scarcity and rising costs.
Substrates are commonly comprised of the following components: peat moss, coconut coir, aged pine bark, wood fiber, vermiculite, perlite, rice hulls and wood chips. Additives can include calcitic limestone, dolomitic limestone, hydrated limestone and calcium sulfate. Newer options are being researched, though.
Peat and bark alternatives include wood, miscanthus, switchgrass, corn stover, wheat straw, fescue stubble, ryegrass stubble, cotton gin trash, hemp fiber, culled nursery trees, unsold Christmas trees, bamboo and biosolids compost.
Owen’s research looked specifically at red pine tree usage, in which the wood is either shredded, chipped or made fibrous. “It will never replace peat but it can be used as an amendment,” he said. Red pine is found across the Great Lakes region, in the Northeast and through the Mid-Atlantic.
To test its efficacy, his team prepared four mixes of substrates: 100% red pine, 80/20 red pine/perlite, 60/20/20 red pine/perlite/peat and 80/20 peat/perlite (all of which were amended with dolomitic limestone and a wetting agent). “We want something lightweight for both the grower and to lessen transportation costs,” Owen said.
The seeds of five species – Chinese cabbage, cucumber, French marigold, radish and tomato – were sown in five five-inch diameter containers filled with each of the four prepared substrates. The team found that after 14 days there were no negative effects on germination from phytotoxicity or chlorosis.
They also wanted to judge performance, so a plant growth trial was performed with Calibrachoa, petunia, French marigold, tomato, geranium, vinca and pepper, each transplanted into five-inch containers filled with each substrate. Owen reported they did see chlorosis with the 100% pine substrate, but some species had no issue with any of the mixes.
Their conclusion was that substrates with 60% to 80% red pine components produce similar or slightly reduced plant growth to peat (which was attributed to the substrate’s greater than 6.2 pH).
“We discovered 60/20/20 was a very nice mix,” Owen said. “I recommend growers who are willing to try [something different] formulate or amend their greenhouse substrates to contain 60% red pine tree in combination with peat and perlite – but they must routinely manage the substrate pH.”
Another route Owen tested for red pine usage was substrate layering. The goal of the practice is to improve drainage and moisture dynamics and optimize nutrient use efficiency.
Again, different combinations were scrutinized. Layers were tested in 4.5-inch pots, true quarts, six-inch pots and gallon pots. The combinations included 100% pine bark; fine pine bark on top of coarse pine bark; traditional pine bark on top of coarse pine bark; and a pine bark/peat mix on top of coarse pine bark.
Owen said the crop growth was similar or superior for containers with substrate layering versus traditional, non-layered substrate-filled containers. Reduced irrigation volume and nutrients did not reduce plant growth. The pots with the coarse material on top also reduced moisture-caused issues and increased dry mass.
“This shows promise in translating to the greenhouse industry,” Owen said. “A 50/50 mix of pine bark and peat/perlite showed favorable comparison to 100% peat/perlite.”
He did offer the caveat that his team did find it was more feasible to layer in larger containers (true quart and up) versus smaller ones. He also said the layering may not be the best idea for hanging baskets either, due to weight. He suggested growers do their own in-house trialing with these mixes too.
In addition to peat alternatives, Owen’s team also considered perlite alternatives. Specifically, they tested how cherry pits might work. He noted that in 2021, 44% of all U.S.-produced perlite (mined, fired and milled) is used by the horticulture industry. He also mentioned that the U.S. is the second largest cherry producer globally – 74% of tart cherries are produced in Michigan, and Wisconsin and New York are also large producers. However, cherry pits are usually destined for the landfill.
Owen wanted to see if those cherry pits could be utilized rather than scrapped. In a trial testing this idea, they grew plants in 80% peat with either 20% perlite or 20% dried cherry pits mixed in.
He reported there was slightly reduced water holding capacity/increased air with the cherry pits, and there was no negative growth difference due to any phytotoxicity. The pits do have a higher pH, though, so they may not be great for the greenhouse – but perhaps they could work for the nursery industry.
by Courtney Llewellyn