In the Garden | The stars of fall | Gardening
Autumn flowers are among the most beautiful of the year as they have to wait an entire season to finally show their splendor. In addition to their beauty, they are a valuable source of food for late-growth pollinators, which can be particularly important for migratory species such as monarch butterflies.
Asters are the stars of autumn in the natural world. They embellish prairies, forest edges, roadsides and other places in the landscape with cascades of daisy-like flowers. The species in their family (Asteraceae) are diverse and numerous, with over 250 plants known around the world as “asters”.
From the 1990s onwards, botanists were able to take a closer look at asters with the help of DNA tests. New and interesting genetic differences emerged that led to the reclassification of many species, changes to botanical names, and the removal of the 180 species native to North America from the genus Aster.
This has been a tough move for many, as aster has been the generic name associated with so many species for so long. The majority of North American asters have been moved to the genus Symphyotrichum, which certainly doesn’t roll off the tongue like aster. Although research provided the basis for a new classification decades ago, it has been slow to catch on in nurseries and others, creating some confusion about which plants are “asters” and which are not, and making matters difficult for gardeners.
While this type of confusion is typical of many plant name reclassifications, it appears that the changes among asters have been one of the slowest accepted and most discussed that I have seen in my botanical career. It wasn’t until 2015 that the UK’s Royal Horticulture Society officially adopted the new names, and I still see old botanical names today.
However, there is some consistency in naming if we just stick to the common name Aster. In Greek, “aster” means “star”, which stands for the flower structure of the plant.
Aster flowers consist of a bright yellow to orange center that is filled with tiny disc flowers, sometimes in the hundreds. This cluster is surrounded by ray florets, each of which has a long petal-like structure called a ligule that extends outward to form a neat star-shaped flower. Ranging in color from white to pink, blue, or purple, these leaf membranes act like petals on many other flowers, attracting pollinators and drawing attention to the nutrient-rich disc florets in the center.
Blooming asters are always a wonderful harbinger of the autumn color, with a number of small-flowered game species such as At a time in the growing season when so many other species are blooming, the asters provide an invaluable flower resource for pollinators.
In cultivation, asters provide the necessary aesthetic boost at this time of year, with many of them producing a consistently huge bloom. New England aster (S. novae-angliae) is a garden favorite of mine, with its towering stems of purple to pink flowers in autumn. It prefers full sun and well-drained, fertile soil. Height can be an issue with this plant as it can easily reach eye level and has a tendency to tip over without assistance. Pulling back the stems a few times or shearing them during the season works well to reduce height and encourage bushiness, although dense foliage can cause problems with powdery mildew. I recommend dividing this perennial every two years to revitalize the plants and keep the stem density low for better air circulation.
Another favorite of mine that is a bit smaller is the aromatic aster (S. oblongifolium). It has similar purple flowers that bloom a little later in my garden than the New England aster. It does well in a wider range of soils and prefers full sun. With its shorter height (2 to 3 feet) and its aggressive, spreading habit, it works wonderfully as a larger ground cover that takes up readily available space and fills in well around other larger, established plants.
For locations with some shade, I enjoy smooth blue asters (S. Leave). It usually reaches heights between the above two asters with light purple flowers that appear in late September through October.
Asters are certainly not a carefree perennial if a picture-perfect look is your goal. All benefit from regular division and tend to be spread through seeds. Spreading can be limited by clipping flower heads in the fall, although their opportunistic habitat can really help them displace weeds in gardens with enough space.
For me, the rewards of late-season flowering has always outweighed other factors, and the pollinators in my garden show their buzzing approval when they devour these plants in the fall.
Ryan Pankau is a horticultural instructor with a UI extension and oversees the Champaign, Ford, Iroquois and Vermilion districts. This column also appears in his “Garden Scoop” blog at go.illinois.edu/GardenScoopBlog.