Results from a Multi-year Evaluation Study of Epimedium Taxa

Abstract

The Chicago Botanic Garden (USDA Hardiness Zone 5b, AHS Plant Heat Zone 5) conducted an evaluation study of 40 taxa of Epimedium from 1995 to 2001. The goal of this project was to select superior taxa based on winter hardiness, ornamental merit, pest and disease resistance, and cultural adaptability. Three plants of each taxon were grown in a site that features a variety of light levels and diverse microclimates. Of the 40 taxa that began this trial, 33 survived to receive final ratings that ranged from excellent to poor. Although a wide variety of data was collected for each taxon, overall ratings were based on four criteria: flower coverage, health quality, overall habit quality and winter hardiness. Among the rated plants, three varieties stood apart from the others: Epimedium `Crimson', E. grandiflorum `Sonoyzki' and E. × versicolor `Neosulphureum'. One of the most significant characteristics that separated the best performers from the mediocre and poor performers was winter hardiness. Five taxa lost all three plants in the first winter of the trial and were not retested. Several other taxa had their overall ratings severely impacted by winter losses. In addition to winter hardiness, data on frost damage, nutrient limitation and rabbit damage were also collected. Epimedium habits varied from clumped to widespreading groundcovers. Of the 33 barrenwort taxa to receive final ratings, nine were determined to have significant potential use as groundcovers. Also, 12 taxa displayed highly ornamental, early-season foliage colors in shades of burgundy, bronze and red.