The 2009 ASHS Annual Conference

Growstones are a light-weight aggregate produced from waste glass and designed to function as an alternative to aggregates such as perlite and parboiled rice hulls (PBH) in providing for drainage and air-filled pore space in root substrates (substrates). Growstones-containing substrates had a higher pH than equivalent perlite- and PBH-containing substrates. The pH increased as the amount (10 to 30%) of Growstones increased as well as over time (0 to 8 weeks) in a greenhouse environment. All Growstones-containing substrates had a pH within acceptable limits ranging from a low of 5.7 for 10% Growstones after 0 weeks to a high of 6.9 for 30% Growstones after 8 weeks. Across time, Growstones-containing substrates had electrical conductivies ranging from 0.23 to 0.47 mS/cm which were within recommended ranges for unused substrates. The ammonium and nitrate concentrations of Growstones-containing substrates ranged from undetectable to 1.75 ppm and 16.3 to 43.5ppm, respectively. There were no consistent differences in ammonium and nitrate concentrations between Growstones-containing substrates and equivalent perlite- or PBH-containing substrates. Growstones-containing substrates had higher sodium concentrations than equivalent perlite- and PBH-containing substrates. Sodium concentrations increased with increasing amounts of Growstones and across time. However, sodium concentrations (25 to 229 ppm) were within recommended ranges. After 0 weeks, Growstones-containing substrates had higher silica concentrations than equivalent perlite- and PBH-containing substrates, but after 4 and 8 weeks, Growstones-containing substrates had higher silica concentrations than only equivalent perlite-containing substrates. Phosphorus, potassium, calcium, magnesium, sulfur and micronutrient concentrations were within acceptable ranges for all Growstones-containing substrates and times.