Fall flowers are some of the best of the year because they take a whole season of waiting to finally display their splendor. Beyond their beauty, they are a valuable food source for late-growing pollinators, which can be especially important for migratory species such as the monarch.
Asters are the stars of autumn in the natural world. They beautify meadows, woodland edges, roadsides and other places in the landscape with cascading daisy-like flowers. The species of their family (Asteraceae) are diverse and numerous, with more than 250 plants called “asters” around the world.
Beginning in the 1990s, botanists were able to take a closer look at asters using DNA tests. New and interesting genetic differences emerged that resulted in the reclassification of many species, the change of botanical names, and the removal of 180 native North American species from the genus Aster.
This was a difficult change for many since Aster was the genus name associated with so many species for so long. The majority of North American asters have been moved to the genus Symphyotrichum, which certainly does not emerge from the tongue like Aster. Although research decades ago provided the basis for a new classification, it has been very slow to spread among nurseries and the like, leading to some confusion as to which plants are and are not. no “asters” and complicates things for gardeners.
While this kind of confusion is typical of many reclassifications of plant names, it appears that the changes among asteris have been one of the slowest accepted and one that I have talked about the most in my botanical career. It wasn’t until 2015 that the Royal Horticulture Society of Great Britain officially adopted the new names, and I still see old botanical names in use today.
However, there is some consistency in the naming if we just stick to the common name, aster. In Greek, “aster” means “star”, which is emblematic of the floral structure of the plant.
Aster flowers consist of a bright yellow to orange center filled with tiny disc-shaped flowers, sometimes in the hundreds. This cluster is surrounded by ray flowers that each have a long, petal-like structure, called a ligule, which extends outward, creating a star-shaped flower. These ligules range in color from white to pink, blue or purple and act like the petals on many other flowers, attracting pollinators and drawing attention to the food-rich disc flowers in the center.
Blooming asters are always a wonderful harbinger of fall color, with a number of small-flowered wild species, such as the heather aster (Symphyotrichum ericoides) teeming with fall blooming borders. fields, along roads and in other open areas. At a time of the growing season when so many other species have finished blooming, asters are an invaluable floral resource for pollinators.
In cultivation, asters provide a much needed aesthetic boost this time of year, many producing a consistently massive flower display. The New England aster (S. novae-angliae) is one of my favorite gardens, with its towering stems of purple to pink flowers throughout the fall. It prefers full sun and fertile, well-drained soils. Height can be an issue with this plant as it can easily reach eye level and has a tendency to collapse without support. Pinching the stems several times or mowing during the season works well to reduce height and promote the bush, although dense foliage can create powdery mildew problems. I recommend dividing this perennial every two years to invigorate the plants and reduce stem density, providing better air circulation.
Another favorite of mine is the aromatic aster (S. oblongifolium), which is a bit smaller. It has similar purple flowers that bloom slightly later than the New England aster in my garden. It grows well in a wider range of soils and prefers full sun. With its lower height (2-3 feet) and aggressive, spreading habit, it works wonderfully as a taller ground cover that easily takes up available space, filling well around other taller established plants.
For places with a little shade, I appreciate the smooth blue aster (S. leave). It usually grows to heights somewhere between the two aforementioned asters with light purple flowers that occur from late September through October.
Asters are definitely not carefree perennials if your goal is to look perfect. All benefit from regular division and tend to spread by seed. Spread can be limited by trimming flower heads in the fall, although their opportunistic habitat can really help them overcome weeds in gardens with enough space.
For me, the reward of late season flowers has always outweighed other factors, and the pollinators in my garden show their buzzing approval when they gobble up these plants in the fall.
Ryan Pankau is a Horticultural Educator with UI Extension, serving Champaign, Ford, Iroquois and Vermilion counties. This column also appears on his ‘Garden Scoop’ blog at go.illinois.edu/GardenScoopBlog.