October is the time to enjoy the beauty of asters. You’ll notice from the scientific name that, once again, the taxonomists have been busy re-naming another horticultural favorite. This time, I’m more sympathetic to the taxonomists’ reasoning, but I still have to wonder at what morphological (physical) characteristics led these scientists to a combination of symphyo (to unite) and trichum (hair). However, since symphyotrichums remain in the family Asteraceae, I’m going to join other horticulturists in continuing to refer to these plants as asters.
Aster ‘Purple Dome’ is a cultivar introduced by Dr. Richard (“Dick”) Lighty, now retired from the Mt. Cuba Center in Delaware. The Mt. Cuba Center has also provided several other popular plant introductions, including Symphyotrichum laeve ‘Bluebird’ (Aster laevis ‘Bluebird’), Eupatorium rugosum ‘Chocolate’ (White Snakeroot), and Cornus sericea ‘Silver and Gold’ (Variegated Red-Osier Dogwood). Purple Dome is a dwarf hybrid of the New England (novae-angliae) aster, growing to only 18″ high, although it can spread to 24″ wide. It is noted for its resistance to powdery mildew, commonly seen on species asters in the fall. Although drought tolerant once established, it prefers a moist soil but dislikes wet feet, so don’t over-water. The plant can be pinched back in late June, but I haven’t found this necessary yet to achieve a mass of fall blooms. Usually, Purple Dome will start producing flowers in September, although this year I noticed that mine didn’t start blooming until the beginning of October.
The only serious insect pest affecting asters is the Aster Leafhopper, a vector (carrier) for Aster Yellows. Aster Yellows is a phytoplasma–similar to bacteria, but with no cell wall–for which there is no cure. Symptoms of Aster Yellows include flower petals which develop a green pigmentation and abundant production of petals and sepals, all appearing rolled and bunched. Aster Leafhoppers overwinter as adults in Texas, Oklahoma and Arkansas. In the spring, they ride the southerly winds into northern states, including Minnesota and Wisconsin, among others.
Since Aster Yellows can affect other types of flowers (and vegetables) besides asters, it’s worthwhile monitoring for Aster Leafhoppers, especially since they are capable of producing three generations per year, with as many as 200 offspring in a breeding season. If leafhoppers are detected in home gardens, they can be controlled by insecticidal soap.