Growth of Vinca and Geranium In 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). There were no differences in shoot height, shoot dry weight or root dry weight of ‘Cooler Grape’ vinca (Catharanthus roseus) plants grown in sphagnum peat-based substrates containing 10% to 30% Growstones, perlite or PBH. Vinca grown in all root substrates were of marketable quality. Shoot height of ‘Orbit Cardinal Red’ geranium (Pelargonium x hortorum) grown in the 30% Growstones substrate were shorter than vinca grown in the 30% perlite substrate. No other differences occurred in geranium height between Growstones-containing substrates and equivalent perlite- or PBH-containing substrates. Geranium shoot dry weight grown in the 30% Growstones substrate were lower than for vinca grown in the 30% perlite substrate. No other differences occurred in geranium shoot dry weight between Growstones-containing substrates and equivalent perlite- or PBH-containing substrates. Root dry weight of geranium grown in the 10% Growstones substrate was higher than for geranium grown in the 10% PBH substrate, but root dry weight of geranium grown in the 15% Growstones substrate was lower than for geranium grown in the 15% PBH substrate . No other differences occurred in geranium root dry weight between Growstones-containing substrates and equivalent perlite- or PBH-containing substrates. Plants of vinca and geranium grown in substrates containing 10% to 30% Growstones were of marketable quality.