The 2012 ASHS Annual Conference

Perlite is the primary aggregate in greenhouse substrates and is the most expensive (by volume) component of greenhouse mixes.  Due to rising costs and the non-renewable nature of perlite; alternative aggregates are currently being investigated for use.  This research evaluated loblolly pine (Pinus taeda L.) chips as one such alternative. Loblolly trees were harvested, chipped and hammered milled through a ¼” screen on 8 Mar. 2011. Peat-based substrates were amended (v/v) with 20 or 40% perlite (PL) or woodchips (WC) for a total of four substrates.  All substrates were amended with 0, 1.4, 2.7, 4.1, and 5.4 kg·m³ dolomitic limestone, resulting in 20 substrates treatments. Rooted liners of Chrysanthemum x morifolium ‘Mildred Yellow’ were transplanted into six reps of each substrate. Plants were fertigated as needed with 200 ppm nitrogen (derived from a 20-10-20 soluble fertilizer) and pour-throughs were conducted weekly to monitor substrate pH.  After nine weeks shoots were harvested for dry weight determination.  Shoot growth of chrysanthemum in all substrates containing PL or WC increased as lime rate increased from 0 up to 2.7 kg·m³ where plant growth was greatest. Shoot growth was statistically similar and showed the same growth trends between PL and WC substrates (at 20 and 40%) and at all lime rates in this study. Substrate pH was often higher in 40% PL or WC than in 20% all lime rates and at all measuring dates. pH of WC amended substrates was always equal or higher than PL at the same percentages and at the same lime rates throughout the study. Results show that wood chip aggregates can replace perlite in a peat-based substrate with no changes in plant growth or liming requirements when growing chrysanthemum.