By Carl Wilson, extension agent, Denver County office of Colorado State University Cooperative Extension
Fall in the garden would lose its splendor if it weren't for asters.
Tough and reliable, asters are a natural for dry climates. In fact, many types don't have much success at surviving the winter when kept too moist. About 600 species are known, including several that delight hikers in the Front Range foothills and Colorado mountains.
Among cultivated asters, growth habits range from open branching, 3-foot perennials to compact alpine-type mounds. The work aster is of Greek derivation and refers to the starlike flowers that can be white, red, pink, purple, lavender and blue, mostly with yellow centers.
Though asters generally bloom in late summer and fall, alpine aster (Aster alpinus) flowers in May and June. This little rock-garden plant bears 1 1/2- inch violet flowers, although selections with white, blue, lavender and pink flowers are available. Alpine asters grow best in full sun and well-drained soil.
Wonder of Stafa hybrid aster (A. xfrikartii) is said by many to be one of the 10 best perennials. Named for the town of Stafa, Switzerland, where Carl Frikart created the hybrid, the soft, lavender-blue flowers blend well with most other flower colors.
Plants reach 30 inches in height and are somewhat floppy unless staked for a formal garden appearance. After flowering starts in August, bloom continues until late October.
Another aster improved by European breeders is New England aster (A. novaeangliae). The 1 1/2-inch flowers (shown above) are produced in large, showy heads of white, pink, blue and purple. Plant in full sun and don't allow it to self-seed or the planting will soon revert to a wild type. You can pinch back plants in June to make stockier plants.
Local nurseries sell even more varieties of New York aster (A. novi-belgii), also called Michaelmas daisy. Similar to New England aster, the plants have glossier, more finely divided foliage. The 1-inch flowers come in the full range of aster colors. Heights range from a few inches to 4 feet tall. The locally popular Professor Kippenburg is a lavender-blue blooming type that reaches 15 inches.
Asters are one of the easiest garden perennials to cultivate. Their biggest problem locally is powdery mildew. Disease and spreading both can be controlled by dividing asters yearly in spring, replanting the outer portions and discarding the spent center of the clump.
Combine asters with mauve joe-pye weed, northern goldenrod, white coneflower or the tawny seed heads of ornamental grasses, such as feather reed grass, for a complete fall floral show.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010