Evaluation of accessions of Spiraea alba and Spiraea tomentosa in Indiana

Given the rich genetic diversity in many native US species, evaluations to identify superior genetic material have increased in recent years. We evaluated 7 accessions each of white meadowsweet (Spiraea alba Du Roi [Rosaceae]) and steeplebush (S. tomentosa L.) in Tippecanoe County, Indiana, for their potential as landscape plants in neutral pH soils of the Midwest. Accessions were planted in 2009 and evaluated in 2011 and 2012. All but 2 of the S. alba accessions reached a height of 1 m (40 in), whereas S. tomentosa accessions reached a height of approximately 60 cm (24 in). Spiraea tomentosa plants exhibited more leaf chlorosis than S. alba plants, and the growth of some S. tomentosa accessions was clearly reduced by neutral pH soils. In both species, flowering extended from late May to early August. Accessions from more northern climates flowered earlier than those from more southern climates. In general, S. alba performed better under the conditions of the trial site; however, our evaluation primarily indicates the need to further evaluate the genetic diversity of S. alba and S. tomentosa for selection of superior materials with high potential for success in the managed landscape.