2018 ASHS Annual Conference

With the continued interest in alternative horticultural substrates, specifically wood-based substrates, there remains a void of published information describing the differences in many of the commercially available materials on the market today. The results from many grower trials and independent company R&D trial results are trickling information out to the industry but a thorough overview of products and product differences is needed. A survey of wood substrate materials in North America and Europe was conducted from 2015-2018 during which time as many of the available wood product’s as possible were acquired for the purpose of laboratory and greenhouse testing and comparison trials. In addition to product acquisition, information was gathered (when possible) on the type of machinery and processing techniques that were used to create each specific wood component. Of the 30 plus materials collected, observed, evaluated, or tested there were three different machine types identified that produced most all of the wood products: 1) single or twin screw extruders/retruders; 2) twin disc refiners; or 3) hammer mills. Each machine/processing type creates unique wood particles and unique substrate blends/mixes. The different processing types have different effects on the wood chemical properties and phytotoxic potential of the end product. The three processing methods also have differing abilities to be modified or manipulated to create variations among or within their products (fiber thickness, fiber length, wood particle shape, wood particle size, etc.). Upon evaluation of numerous materials manufactured from each of the three machine types, no one product (or process) is superior to others and each one has pro’s and con’s relative to expense, variability in product offerings, annual maintenance costs, product consistency, properties of the end product material, etc. As commercialization of wood substrates continues, more scientific information and product trial testimonies from growers who choose to use them will be available.