2017 ASHS Annual Conference

Understanding the efficacy of expanded shale as a soil amendment requires studies of different environments, soil types and weather conditions. Amendment to clay soils with expanded shale could break up clay soil, limit compaction and enhance drainage. This research project examined the efficacy of varying levels of expanded shale as they relate to herbaceous ornamental plant growth in Colorado. Soil at the research site is clay and is in a new landscape environment. In the fall of 2015, six different treatments were established involving applications of expanded shale at three levels, with and without compost. Soils were treated with 5 cm of compost, as a control, or 5 cm compost plus 2.5 cm, 5 cm, or 7.5 cm of shale or with 5 cm or 7.5 cm shale without compost. Amendment was incorporated twelve inches deep. Each treatment had five replications and were arranged in a randomized complete block design. Two ornamental herbaceous perennials, Penstemon x mexicali ‘P008S’ and Heuchera sanguinea ‘Snow Angel’ were used in the study. They both have prolonged attractive flowers during the growing season. The beds were watered throughout the 2016 season by an automated system every other day. Weeding was performed by hand. Growth in each treatment was measured starting in April 2016 through the 2016 growing season. Growth in each treatment was measured six times starting in April 2016 through October 2016. Photographic imaging provided a visual record and permitted leaf surface area to be calculated using the program Easy Leaf Area. Growth was measured horizontally in two dimensions for each plant, as well as vertically, measuring to the top of the flowers when appropriate. Plant size increased during the 2016 season but there were no significant differences between treatments for either the Heuchera or the Penstemon. Each plant showed similar variability in growth during the 2016 season independent of treatment. The same measurements will be taken for the 2017 growing season along with assessment of root morphology at harvest. If expanded shale is shown to be an effective means to help break up compacted clay soil and improve drainage it could prove a valuable addition to Colorado landscapes and beyond.