Landscape Architect & Specifier News

JAN 2019

LASN is a photographically oriented, professional journal featuring topics of concern and state-of-the-art projects designed or influenced by registered Landscape Architects.

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Above: View across Plot 2 into Plot 3 in July 2018, showing plant failures. Right: The graph shows soil moisture readings taken every 30 minutes from June 1, 2018 to July 1, 2018, three years into establishment of these gardens. This box and whisker plot shows the range of readings (the smaller the box, the closer each reading is to one another thus less fluctuation in moisture, thus less stress to the plants). The dark blue arrow indicates the range of plant available water in the Haydite Bioblend and the traditional sandy loam. It is clear that the Sandy Loam mix experiences much wider range in soil suction (how hard is the soil fighting the plant for water) and spends most of the time above the Plants Available Water (PAW) limit of that soil. Conversely, the expanded shale creates a soil environment, which maintains a near constant level of soil moisture well within the PAW range. Furthermore, the expanded shale allows a much wider range of soil suction without losing PAW. 34 Landscape Architect and Specifier News a local product in Cleveland called Haydite BioBlend. Haydite is a expanded shale that has great properties for this type of use, including: high absorption rates, nutrient holding capacity, improved air exchange, high surface area for microbial activity, and as you guessed it, very high plant available water holding; all while draining as fast, and sometimes faster, than the high sand blends we are used to. Comparing this alone to the survivorship of plants in each garden after three years of growth and the story becomes quite clear; with a 48% survival rate in the sandy loam soil, versus 96% in experimental soil A (60% expanded shale, 20% compost, 20% pine fines), or even 76% in experimental blend B (60% expanded shale, 40% in situ soil, in this case a silty clay). We'll be releasing the full study soon for publication showing a number of stress factors, including poor PAW, and render the high sand soils we are used to as inferior media blends for stormwater bioremediation. The hope is to spur conversation and feedback into the design and specification process of bioremediation. Let's talk, horticulturists and architects and engineers. We all want the same thing, a more beautiful and functional world.

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