Betting on biochar

You’ve used charcoal as fuel to grill a burger. But would you consider using it as fuel to grow your plants?

Biochar is an ancient technology that has been used in agriculture for more than 2,000 years. It is a growth and yield booster. Its pure carbon structure retains nutrients and acts as a high-rise apartment for soil microbes. It also helps in moisture retention and has been used for soil contamination remediation. Biochar also provides a home for beneficial soil biology, so if you are using any form of beneficial microbes in your production practices they will find a home inside biochar particles.

In the past decade, the steadily decreasing cost and increasing availability of biochar is allowing larger production nurseries to incorporate it into their regular practice.

Mark Highland, president of The Organic Mechanics Soil Company, says production nurseries should consider biochar because it lets them use less water and less fertilizer to achieve the same quality plant.

“Plants grown in biochar-amended soil also seem to be healthier than counterparts grown in a control group,” Highland says.

Biochar is not a fertilizer, but it helps retain fertilizer in the media instead of nutrients leaching from containers. For container nurseries, a layer of biochar in the bottom of the pot keeps good drainage at the bottom, while also acting as a filter to help catch nutrients before they run away down the drain.

“Holding fertilizer in the root zone helps fertilizer efficiency and can reduce leach and runoff,” says Jim Loar, CEO of Cool Planet, whose Cool Terra biochar product is used in a wide range of horticultural environments. “We’ve also seen faster, more vigorous plant establishment – getting a plant off to good start can lead to a healthier plant long-term.”

Recent research

While at the University of California – Davis, Andrew J. Margenot led a team of researchers on a project investigating biochar’s potential as an alternative to peat moss. Similar to charcoal, biochar is produced through a process called pyrolysis, or heating to high temperatures in the absence of oxygen. And like charcoal, it can be derived from virtually any organic substance. Margenot, now an assistant professor in the Department of Crop Sciences at University of Illinois Urbana-Champaign, led the evaluation, testing the substance by measuring plant performance and pH adjustment on marigolds.

The study, which can be read in full in the journal Industrial Crops & Products, demonstrates that softwood biochar can be considered as a full replacement for peat in soil-free substrates, and even at high rates (70 percent total substrate volume) does not require pH adjustment for marigold production. Margenot’s team suggests that crop- and biochar-specific considerations and economic potential should be investigated for wider application. For now, there are no plans to expand the study to traditional nursery crops. That could change if funding becomes available.

“Examining biochar-based substrates for plants with longer production time would be a useful next step,” Margenot says. “Additionally, comparing the longevity of biochar-based substrates for multiple uses would also be helpful information for producers.”

Margenot stresses that the marigolds in his study were under high fertigation, as the project was designed to mimic practices by local greenhouse producers.

“Some folks have asked if biochar alone can do away with the need to fertilize,” Margenot says. “This is not the case, unfortunately. Like any other substrate, fertigation would still be necessary.”

Since moving to his new academic home at UI Urbana-Champaign, Margenot sees potential avenues for biochar to make an impact. One interesting future research angle would be to assess various biochars that reflect economically feasible feedstocks for their production in a specific region.

“I think a locally relevant biochar would be one made of corn residues,” Margenot says. “There would be endless feedstock for such biochars in the Midwest.”

In the UC Davis study, the biochar used was sourced from softwood that is often abundant from the nearby logging or forest thinning operations in the Sierra Nevada. It was manufactured by Pacific Biochar, a California-based company that was founded by Josiah Hunt. Hunt was a landscape ecologist who began producing, processing and improving biochar in 2009. Growing interest in the business led him to found Hawaii Biochar Products, where his feedstock was macadamia nut shells. That company expanded across the ocean and was renamed Pacific Biochar to reflect its growth.

“Charcoal has a long history of use in horticulture,” Hunt says. “It happened essentially everywhere that humans and fire and agriculture were in the same place. Because before the advent of Home Depot or fertilizer stores, you just had to use what you got. And people cooked on fire, so residues of ash and charcoal were ubiquitous. They pretty much always ended up in the garden.”

Hands-on experience

Mark Crawford owns Loch Laurel Nursery in Valdosta, Ga. He specializes in camellias, a notoriously slow-growing shrub, and he’s used biochar two different ways in his nursery. His first objective was to cut out a year of growing time, so the camellias begin to take off in the second year instead of the third. He’s transplanted about 60 plants with biochar and he’s seen growth gains and reduced transplant shock.

The second spot where biochar makes a big difference is in propagation. Some of Crawford’s camellia cuttings lack a robust root system, which makes transplanting difficult. He incorporates biochar into his rooting media at a 5-10 percent rate. Mixing in at a higher rate offers only diminishing returns. Growers may be able to remove a corresponding percentage of perlite, if the biochar they’re using has similar properties and particle size.

Crawford thinks propagation is the best bet for biochar in nurseries, because of the attraction of improved post-transplant growth after moving from cutting propagation trays to 1-gallon containers.

“I know how sensitive nursery people are to cost,” he says. “The product is relatively expensive. So I thought ‘Where can you get the most bang out of your buck?’ When you’re rooting cuttings, you’re basically treating every plant at a small scale. You’re literally treating thousands of plants with a small amount of material.”

Crawford says biochar isn’t for everybody. It may depend on your product mix.

“I don’t see any benefit with lorapetalums or ligustrum or any of those things that grow like weeds,” he says. “But the slower-growing plants, like camellias, rhododendrons, even azaleas, there’s where you see the benefit.”

He suggests trying it on other high-value plants like Japanese maples or fruit-bearing trees as well.

Not all biochars are created equal. Even beyond the differences in source material, different biochar manufacturers have different production processes. Is it ready to use out of the bag? Growers should ask about the use rate, as well. Cool Planet’s Loar says materials can mean the difference between measuring product in tons per acre or pounds per acre.

“In typical nursery soil medias, we’d look at a 3-5 percent incorporation rate in the soil blend,” Loar says. “If it’s production in a field setting, probably around 1-2 percent.”

Highland’s company provides biochar in both forms, pre-inoculated and ready to incorporate, and raw biochar for those brave souls that want to do their own research and inoculation procedures.

Growers should also account for ash. In some cases high levels of ash are an advantage; in others it’s a disadvantage. Hunt says ash content in biochar materials will range from 5 to 30 percent. Learning about a new substrate may be daunting, but the benefits are real.

“Improved nutrient management in potting media is a unique benefit that biochar can offer,” Hunt says. “Biochar can offer water holding capacity, so too can peat moss or coco coir. Biochar can offer drainage and aeration, so too can perlite or cinders. But in a competition for nutrient management, biochar is a clear winner.”

For more: biochar.ucdavis.edu; biochar-us.org