Wood Fiber as an Alternative on Peat-reduced Substrates

In our article on why professional plant production is moving away from peat we explore the most widely used peat alternatives. As the industry shifts towards peat-reduced and even peat-free growing media, wood fiber is gaining popularity thanks to its versatility. It can be used on its own in 100% wood fiber substrates or blended with materials such as bark, coir, or compost. In this article, we explore the different types of wood fiber, their technical characteristics, key evaluation criteria, and the main considerations for their use.

What is Wood Fiber for Ornamental Horticulture?

As you would expect, wood fiber means fibers of wood but is a general term that does not specify: 

• the species or mix of wood species used to create the fibers 
• the age or the parts of the trees (cuttings, branches, timber by-products, whole trees) 
• the mechanical manufacturing process using machines such as extruders, hammer mills, disc refiners, and knife ring flakers 
• the chemical manufacturing process—altering the C:N ratio by N fortification (impregnation) 
• the physical structure and inherent chemical nature of the product 

Different Kinds of Wood Fibers

As a result, commercial wood fiber products can vary significantly in physical and chemical properties. What might vary the most are pH, porosity, water and nutrient holding capacity, and potential toxicity depending on the age and manufacturing process of the material as well as geographical origin.  

1 Wood Fiber from softwoods/conifers (the market standard)

For instance in the US, yellow/loblolly pine (Pinus taeda) is mainly used, while in Europe European species of pine (P. sylvestris, P. maritima, P. pinaster, P. nigra) are the main sources. There are reports in the literature of  Larix (larch) and Picea (spruce) species also being used for wood fiber production, as well as some anecdotal evidence of waste material from commercial wood products and crops being used to produce wood fiber for the horticultural market. 

2 Wood Fiber from hardwoods/detannized chestnut (industrial woody by-products)

While softwood conifers remain the primary raw material for commercial wood fiber, detannized chestnut wood fiber (Castanea sativa Mill.)—a by-product of the industrial tannin extraction process—has also been evaluated as a substrate component. When properly extruded or mechanically processed and biologically stabilized, detannized chestnut wood fiber can be safely incorporated into professional growing media.

3 Wood Fiber from Emerging Herbaceous Fibers (e.g., Miscanthus)

Beyond tree-derived fibers, lignocellulosic materials from perennial crops like giant miscanthus (Miscanthus × giganteus) are transitioning from experimental trials to commercial application. Once extruded, miscanthus yields a lightweight, highly porous matrix with excellent aeration. While requiring nitrogen management due to its high C:N ratio, it could be a sustainable, renewable alternative for peat-reduced substrates.

 To date, there have been over two dozen different hardwood and softwood tree species evaluated for their potential use as growing media components. Most have been found to be unsuitable due to poor plant growth, availability, cost, processing issues, or other reasons. However, ornamental plant growers should be reassured that wood fibers available in the market are suitable for ornamental production.

How Wood Fiber Contributes to the Substrate

 It is already well known, for example, that peat-based mixes containing 20–30% wood fiber can constitute high-quality growing media which can reliably produce good plant/crop growth in a variety of plant species. Peat works as a “blank canvas” and can form exceptional growing substrates on its own, as well as in combination with coir, bark, or compost.

What Ornamentl Growers Need to Consider When Using Wood Fiber

As mentioned on part two of this article, the most important thing for growers, is to know

• the exact composition of their wood fiber
• the parameters to be checked before using the new growing media as well as during plant production, because fluctuations in wood fiber-based substrates are bigger than in peat. To know the most important parameters to monitor, go to this guide to measuring tools for substrates in ornamental horticulture

Conclusion

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