Astilbe and Coneflower Growth as Affected by Fertilizer Rate and Substrate Volumetric Water Content

Improved irrigation and fertilization practices, such as reduced applications, are needed to improve the sustainability of container plant production. The objective of this study was to assess growth of Visions astilbe (Astilbe chinensis 'Visions') and Mellow Yellow coneflower (Echinacea purpurea 'Mellow Yellow') grown at two controlled-release fertilizer (CRF) rates (100% or 50% of the medium bag rate) and two volumetric water contents (VWC; 40% and 18%). For coneflower, there were no significant treatment effects for height, growth index, shoot dry weight, or leaf size. There was a significant VWC effect on number of flowers with the 40% treatment having more flowers (5.6) per plant than the 18% treatment (2.7). Shoot dry weight, growth index, and leaf size of astilbe were greater for the 40% VWC treatment than the 18% VWC treatment with no fertilizer rate effect. Astilbe height and number of flowers was not significant. These results indicate that there is a species-specific effect of VWC on growth whereas reduced fertilizer applications are possible for both species without impacting growth. Although a substrate VWC of 18% is likely too low to produce salable plants, a VWC below 40% can potentially be used to support adequate growth.