Title: Assessment of physical properties and stonecrop growth in green roof substrates amended with compost and hydrogel.e:
Author(s): Michael W. Olszewski, Marion H. Holmes, and Courtney A. Young
Source: HortTechnology
Pages: 438-444
Published: April 2010
Abstract:
There is a lack of quantifiable data concerning physical analyses specific to shallow-depth green roof substrates and their effects on initial plant growth. Physical properties were determined for green roof substrates containing (by volume) 50%, 60%, or 70% heat-expanded coarse slate and 30% heat-expanded fine slate amended with 20%, 10%, or 0% landscape and greenhouse waste compost. Each substrate also was amended with hydrogel at 0, 0.75, 1.50, or 3.75 lb/yard3. There were no differences in total porosity among substrates containing 0%, 10%, or 20% compost, although total porosity increased for all substrates amended with hydrogel at 3.75 lb/yard3. Container capacity increased in substrates containing 3.75 lb/yard3 hydrogel, except for substrates containing 10% compost where hydrogel had no effect. Aeration porosity decreased when 10% or 20% compost was added to substrates. Determination of aeration porosity at an applied suction pressure of 6.3 kPa (AP-6.3 kPa), indicated that AP-6.3 kPa was higher in substrates containing 0% compost than substrates containing 20% compost. Shoot dry weight and coverage area measurements of ‘Weihenstephaner Gold’ stonecrop (Sedum floriferum) and ‘Summer Glory’ stonecrop (Sedum spurium) were determined 9 weeks after plug transplantation into substrates. Both stonecrop species responded similarly to substrate amendments. Initial plant growth was greater in substrate containing 20% compost and 3.75 lb/yard3 hydrogel than nonamended substrate resulting in 198% and 161% higher shoot dry weight and coverage area, respectively. Alkaline heat-expanded slate and acidic compost components affected initial pH of substrates, but there was less variation among final substrate pH values. We conclude that compost and/or hydrogel amendments affected physiochemical properties following incorporation into slate-based green roof substrates, resulting in greater initial plant growth, and that these amendments may have practical applications for improving growing conditions on green roofs.
