Extension Educator, Horticulture
Physically, emotionally and horticulturally we all need plants that hang on to the glitter end of the growing season. Late bloomers get us through the dreary days of fall and give butterflies and pollinators a much needed late season meal.
In October, if you look to gardens, prairies, woodlands and roadsides, asters are the stars of the glow. Many species are in the Aster genus or at least use to be in the Aster genus. I guess Aster was just too easy to spell. Scientifically many are now in the Symphyotrichum genus.
Our native asters offer non-stop blooms from late summer into fall with eye-popping colors, but unfortunately are not always available for purchase. Although garden asters are typically selected for full sun gardens, plenty of native asters are found happily growing in woodlands with part shade.
In horticulture many hybrids of various species exist to give us the best of each species with a wide range of flower colors (pink, red, purple, blue, or white) and plant sizes (2-5 feet tall). Asters are a magnificent complement to fall mums. Another welcome attribute is their ability to survive our winters and summers to be long-lived perennials.
Despite their name New England asters (Symphyotrichum novae-angliae or Aster novae-angliae) are found throughout North America. They often dot the roadsides with their purple daisys. Although smaller cultivars exist, New England asters can get tall at 3-5 feet. They may flop if they don't have tall sturdy plants to lean on such as tall prairie grasses. If they flop in your garden, be sure to cut them back by one-third in June. The plants will be more compact, have more flowering branches, and will bloom a week or so later.
New England asters may get the fungal leaf disease powdery mildew. It does not kill the plant, but causes the lower leaves to brown and hang sadly on the stems. I usually just strip off the brown lower leaves and the shorter plants in front of asters hide their knobby bare legs. Popular cultivars are selected for disease resistance which include: 'Alma Potschke' (3 feet tall, brilliant pink); 'Honeysong Pink' (3 feet tall, pink); 'Purple Dome' ( 2-2.5 feet tall mound, deep purple); 'Red Star' (1-1.5 feet tall, deep rosy red); 'September Beauty' (3.5 feet tall, deep red); and 'September Ruby' (3-4 feet tall deep rosy red blooms).
The New York aster (Symphyotrichum novi-belgii or Aster novi-belgii) has many cultivars with wildly different sizes and flower colors. Popular cultivars include: 'Prof. Kippenburg' (compact 12-18 inches tall, lavender-blue flowers); 'Celeste' (18-24 inches tall, blue flowers with yellow centers); and 'Crimson Brocade' (2-3 feet tall, semi-double crimson flowers).
Bush aster (Symphyotrichum dumosum or Aster dumosus) is a native, compact 2-foot tall plant. Flowers of blue, purple or pink are prolifically borne from August through October. Cultivars include: 'Wood's Blue' and 'Wood's Pink'.
Frikart's aster (Aster x frikartii) is easily used as a mounded 2-3 foot tall plant of dark green, disease-free leaves with a long bloom period from June to September of pale to dark blue-violet blooms with showy yellow-orange centers. Wet winter soils are often fatal to Frikart's aster so be sure to plant it in a well-drained area or raised bed. With such a long bloom period, it is well worth growing even if it doesn't make it through winter. Cultivars include: 'Monch'; 'Jungfrau'; 'Wonder of Staffa'; and 'Eiger'.
The airy loveliness of the tiny pink and white flowers of the 1-2 foot-tall Calico aster (Symphyotrichum lateriflorum var. horizontale) adds a delicate beauty to the fall garden. The stems are held in horizontal layers with each layer a profusion of flowers. A charming cultivar with dark leaves is 'Lady in Black'.
For more information: http://urbanext.illinois.edu/perennials