Pine Wood Chips as an Alternative to Perlite in Horticultural Substrates: Physical, Chemical, and Cultural Parameters

The past decade has seen an increase in the potential uses of fresh wood in horticultural substrates. During this time numerous academic researchers, substrate (potting mix) manufacturers, and independent growers have tested various wood components and formulations in an attempt to stretch/extend peat or pine bark supplies in both the nursery and greenhouse industries. Loblolly pine has been proven to be the best tree species to make substrates or substrate components. When processed pine wood is amended in peat substrates it has been observed and noted that due to increased air space (porosity) it is likely that perlite is not needed in greenhouse substrates.  Perlite serves as an aggregate in greenhouse substrates and, depending on the specific substrate, is incorporated at rates of 10% to 40% most commonly. Perlite, being expensive, nonrenewable and inorganic has led to interest in finding suitable replacements. Until recently no protocols or specifications have been used to process pine wood, which has resulted in inconsistent and varied end products (substrate components).  Recent advances in wood processing procedures have resulted in pine wood chips (PWC) that are nonfiberous, structurally similar to perlite, consistently reproduced, cost effective, and broadly accessible. Freshly harvested pine trees were chipped and then further processed in a hammer mill through a 6.35 mm screen yielding PWC. Over a two-year period, PWC aggregates were processed and trialed in comparison to perlite at ratios of 10% to 30%.  Experiments were conducted to test/compare: 1) substrate physical properties; 2) chemical properties; 3) fertility requirements; 4) liming requirements; and 5) plant growth regulator (PGR) efficacy/requirements. All laboratory and plant growth trials that were conducted indicate that substrates amended with 10%, 20%, or 30% PWC compared to perlite at the same percentages had no differing effect on substrate physical properties.  Plant trials in substrates amended with 10%, 20%, or 30% PWC compared to perlite at the same percentages also showed no difference in lime, fertility, or PGR requirements for optimal plant growth.  During greenhouse trials (ranging from four to 15 weeks) PWC did not decompose, shrink, or even change color. These results provide evidence across a broad range of cultural parameters that PWC can successfully be used as a replacement to perlite with little to no changes to a grower’s production system.