Asters have long been favorites for the late-season garden. Their cheerful, star-shaped blossoms (the word ″aster″ is from the Greek for ″star″) in shades of white, purple, blue, pink, and red offer a lovely contrast to the yellows and golds of late blooming daisies, the muted tones of ornamental grasses, the glowing oranges, reds, and yellows of changing tree foliage, and the crisp, clear blue of the fall sky. Unfortunately, the beauty of the flowers can be marred by unsightly leaves affected with powdery mildew and rust, especially on the popular New England and New York asters.
To help gardeners choose the best-performing asters for their gardens, Richard Hawke, Plant Evaluation Manager at the Chicago Botanic Garden, recently released the results of a six-year evaluation of 119 different asters, comprising both native and non-native species and cultivars. Plants were grown in full sun and part sun trials at the USDA Hardiness Zone 5, AHS Heat Zone 5 garden and given minimal maintenance to duplicate common home garden conditions, with no insect or disease treatments or winter mulch. Plants were rated on a scale of one to five stars for cultural adaptability, disease and pest problems, winter hardiness, and their ornamental qualities associated with flowers, foliage, and plant habit. Although the goal of the evaluations was to identify asters best suited to the Upper Midwest, the results can be helpful to gardeners in other regions as well.
Here we need a brief aside about the scientific names of asters. Alas for gardeners, taxonomists have decided that the botanical generic name Aster is no longer accurate for our native species. Our North American asters now have a variety of new generic names, all uniformly daunting to pronounce and spell. For example, Aster novae-angliae is now Symphyotrichum novae-angliae; Aster divaricatus is now Eurybia divaricata; and Aster umbellatus now goes by Doellingeria umbellata. Whew! You may find these asters listed by their newer appellations in some catalogs and references, while others still retain the older names.
Seven asters received top billing. Those rating five stars included 'Jindai' Tatarian aster (Aster tataricus); white wood aster, both the species and its cultivar 'Eastern Star'(Eurybia divaricata); 'Snow Flurry' heath aster (Symphyotrichum ericoides); calico aster and its cultivar 'Lady in Black'(S. lateriflorum); and 'Raydon's Favorite' aromatic aster (S.oblongifolium). Nineteen other aster received a four-star rating.
To read A Comparative Study of Cultivated Asters and see rating of all asters in the study, go to Chicago Botanic Garden.