The physiochemical properties of two domestic agricultural biomasses as potential growing media components

Authors: CRISCIONE, KRIS - Virginia Tech; SPINELLI, GERARDO - University Of California; FIELDS, JEB - University Of Florida; Altland, James

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2026
Publication Date: 5/19/2026
Citation: Criscione, K., Spinelli, G., Fields, J., Altland, J.E. 2026. The physiochemical properties of two domestic agricultural biomasses as potential growing media components. HortTechnology. 61(6):1310-1317. https://doi.org/10.21273/hortsci19426-26.
DOI: https://doi.org/10.21273/hortsci19426-26

Interpretive Summary: Reliance on peat based growing media has raised concerns about sustainability, cost, and inconsistent supply. Because peatlands take centuries to form and are sensitive ecosystems, the industry has been seeking reliable, domestic alternatives. The study was conducted to evaluate whether two abundant U.S. agricultural byproducts—palm tree green waste and redwood bark—could serve as components in soilless growing mixes, reducing peat use while maintaining suitable growing conditions for plants. To address this problem, the physical, chemical, and water handling properties of palm fibers and redwood bark were measured, both alone and when blended with common greenhouse substrates. It was found that both palm fibers and redwood bark contain low nitrogen drawdown indices, meaning they are likely to tie up fertilizer nitrogen unless additional nutrients are supplied. Palm fibers were shown to contain high levels of sodium, which may affect plant growth unless the material is washed before use. Physically, palm fibers created mixes with greater air space and faster water drainage, functioning somewhat like a coarse aggregate. Redwood bark, in contrast, contained finer particles and held more water, acting more like peat or coir in blended mixes. When tested in combinations, the redwood bark–coconut coir blend performed similarly to commercial peat based substrates, while mixes containing palm fibers drained more rapidly and required different irrigation strategies. This knowledge can be used by growers and substrate manufacturers to make informed decisions about whether, and how, these materials can be incorporated into production systems. By identifying practical opportunities and limitations associated with palm fibers and redwood bark, growers are given new domestic options that could reduce pressure on peat resources, strengthen supply chain resilience, and support more sustainable horticultural practices. While further research is still needed—especially regarding long term performance and nutrient management—the findings suggest that both materials have meaningful potential within a circular, domestically sourced substrate economy.

Technical Abstract: There are industry-wide concerns regarding sustainability and commercial availability of peat use in horticulture. Providing growers with domestic options can offer flexibility in substrate management decisions and reduce reliance on peat. The objective of this study was to measure the physiochemical properties of two organic domestic agricultural biomass as potential peat reducers. Three substrate components, including 1) palm fiber, 2) redwood bark, and 3) coconut coir, and three substrate composites, including a 1) commercially available peat:perlite (peatlite) mix, 2) 50:50 peatlite: palm fibers mix, and 3) 70:30 redwood bark: commercially available coconut coir substrate were measured for their chemical, physical, or hydraulic properties. The results showed that both palm fibers and redwood bark components contained low nitrogen draw-down indices (p < 0.001). Palm fiber contained the greatest sodium levels across the substrate components (p < 0.001). Palm fibers as a standalone component contained the greatest air space (AS; 0.50 cm3 cm-3) and lowest container capacity values (CC; 0.28 cm3 cm-3) when compared to the other components (p < 0.001). When palm fibers were amended to peatlite, the amended mix had reduced CC when compared to 100% peatlite (p < 0.001). Redwood bark: coconut coir composites contained similar CC and AS values to commercial peatlite. Peatlite composites contained the greatest volume of easily available water (0.27 cm3 cm-3) when compared to a peatlite: palm fiber (0.17 cm3 cm-3) and redwood bark: coconut coir mix (0.20 cm3 cm-3). Peatlite: palm fiber mixes had the greatest pore uniformity when compared to other composites (p < 0.001), which resulted in a more gradual loss of volumetric water content with decreasing water potentials. However, the peatlite: palm fiber mix had the most rapid moisture loss in moisture redistribution models within a 24-h period. These results provide baseline information regarding the physiochemical and hydraulic properties of two domestically sourced materials, palm fiber and redwood bark. More research is needed to qualify their potential use as a substrate component in containerized horticulture production.