Physical Properties of Growstones-, Perlite- and PBH-Containing Root Substrates

Growstones are a light-weight aggregate produced from waste glass bottles and containers. They are designed to serve as an alternative to such aggregates as perlite and parboiled rice hulls (PBH) in providing for drainage and air-filled pore space in root substrates (substrates). As compared to horticultural perlite, Growstones had a higher air-filled pore space (53%) than perlite (30%) and a lower air-filled pore space than PBH (68%). Growstones and perlite had similar water-holding capacities (34 and 32%, respectively), but Growstones had a higher water-holding capacity than PBH (21%). Growstones had a higher bulk density (0.19 g/cubic cm) than both perlite (0.17 g.cm^-3) and PBH (0.10 g^.cm^-3). Sphagnum peat-based substrates containing 10% to 30% Growstones had a similar or higher air-filled pore space than substrates containing equivalent amounts of perlite, but a lower air-filled pore space than those containing equivalent amounts of PBH. Increasing the amount of any of the aggregates increased the amount of air-filled pore space. Substrates containing 15% or more Growstones had higher water-holding capacities than equivalent perlite- and PBH-containing substrates. Increasing the amount of any of the aggregates decreased the water-holding capacity of the substrates. Substrates containing Growstones had higher bulk densities than equivalent perlite- and PBH-containing substrates. The days required for Growstones-containing substrates to dry from container capacity to 50% moisture content and to complete drying was similar to that of equivalent perlite-containing substrates but higher than that of equivalent PBH-containing substrates.