Garden Asters

Published: September 1, 2008

Few things are as depressing to the avid gardener as the end of the growing season. Thee shorter days and cooler temperatures of September tends to remind us that the first killing frost is not too far in the distance. However, autumn is the time of year when some ornamental plants are just coming into their full glory and garden aster is one of those plants. They bear petite, daisy-like flowers that are one to two inches in diameter and come in a wide array of vibrant colors including some of the truest blues to be found anywhere in the plant world. At a time when many gardeners are making one last trip to the local nursery for hardy chrysanthemums, garden asters should be considered also. They share many of the same cultural requirements with mums making them an ideal companion plant in the fall garden.

Aster actually is a genus of plants containing 250 species. Garden aster, along with the likes of zinnia, marigold, dahlia, chrysanthemum and many, many other useful garden species, is a member of the Asteraceae (formerly Compositae) family. The word Aster is derived from a Greek word meaning “star” and refers to the star-like shape of the flower. Garden aster (as well as all members of the Asteraceae family) bears a compound flower known as a head consisting of disc florets that comprise the center or eye, and ray florets that radiate from the eye to form what most people erroneously refer to as the petals.

Most garden asters belong to one of two different species: Aster novi-belgii (New York Aster) or A. novae-angliae (New England Aster); both are native to North America and hardy to zone 4. Important related species include A. tongolensis (East Indies Aster) and A. lateriflorus ‘Horizontalis’ (Calico Aster). Plant breeders have succeeded in improving the wild aster when selecting for compact plant habit and different flower colors. Garden aster often goes by the common name of Michaelmas Daisy; the latter taken from the fact aster blooms around Michaelmas Day (or the feast of St. Michael the Archangel) which is observed on September 29th.

As previously mentioned, the culture of aster is very similar to that of chrysanthemum. Like chrysanthemum, aster is a short-day plant meaning that it requires a long, uninterrupted period of darkness in order to bloom. The long days of spring and early summer promote vegetative growth in aster; the shorter days of late summer trigger flowering to occur. Aster enjoys a full-sun exposure in a well-drained soil of average fertility. The addition of well-decomposed organic matter can help to loosen tight soils. Garden asters purchased in bloom growing in containers need only to be watered; those established in a perennial garden should be given only modest amounts of fertilizer during the growing season since excess fertility leads to tall, “floppy” plants. Garden asters are relatively insect-free but do suffer from several troublesome diseases including aster wilt (yellows) and powdery mildew. Several new cultivars have been developed that are more tolerant of mildew than some of the older, more familiar cultivars.