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We’re going to get back into highlighting students working on the Soilless Substrate Science project. This week, we have George Buss from North Carolina State University. 

I'm currently a master’s student working with Dr. Brian Jackson in the Horticultural Substrates Lab at North Carolina State University. I recently completed the first year of my program, where my research has focused on evaluating different wood species as soilless substrate components and investigating how the physical placement of wood materials within a container influences plant growth.

One of my recent projects examined the use of willow biomass (Salix spp.) as a substrate component for greenhouse crop production. We selected willow because of its established use as a short-rotation bioenergy crop, its ability to produce large amounts of biomass in a relatively short period of time and its tolerance of a wide range of environmental conditions. As the S3 project seeks to identify feasible domestic substrate materials, willow represents a promising renewable resource that could help meet the increasing demand for soilless substrates.

For the willow project, we first processed coarse willow tree chips through a hammermill before creating substrate blends of 25%, 50% or 75% (by volume) processed willow wood amended to peat. The wood inclusion rates were replicated using two potting methods: incorporated or stratified. At each inclusion rate, the incorporated and stratified treatments contained the same amount of willow; the only difference was its physical location within the container. Greenhouse growth trials have been conducted (Fall 2025 and Spring 2026) using different plant species, container sizes and production times.

The growth trials have produced several interesting results. During a short three-week growth trial, tomato and marigold plants grown in stratified substrates containing up to 75% willow wood performed comparably to plants grown in the peatlite control, whereas for the incorporated wood treatments, plant growth was comparable only up to the 50% inclusion rate, above which plant growth was reduced.

Results from a longer six-week growth trial yielded slightly different crop responses. Tomato growth was reduced at willow inclusion rates of 50% and greater in both the incorporated and stratified treatments, whereas marigold growth remained comparable to the control at inclusion rates up to 75% regardless of how the willow wood was amended in the substrate/container.

Taken together, these trial results demonstrate that willow wood has strong potential to be a domestically sourced renewable feedstock for substrate use. In all growth trials (and across all species and container sizes) up to ~50% willow wood produced plants of equal size and quality regardless of inclusion method, which is comparable to previous works on several conifer tree species that have been evaluated as wood substrates.

It's also likely that management practices (optimized irrigation and fertility) could be modified (dialed in) to further enhance plant growth at even higher rates of wood. These findings also suggest that wood incorporation method may influence the amount of wood that can be used in substrates, especially for short-term crop production—a concept I'm currently investigating.