Wildflower is published quarterly by the Wildflower Center. Its content is national in scope with articles about the conservation and use of native plants as well as news from the Wildflower Center. A subscription is provided to Wildflower Center members as a benefit of membership.
Super Stars - Fall 2009
After the dog days of summer, cooler autumn temperatures are often welcome, but take a look around your garden at this time of year and you might have the urge to go back indoors. Leaves crisped from the hot summer sun and spent flowers hanging on past their prime make a garden look a little dreary – unless you plant a fall favorite like native asters.
Many of the numerous aster species are indigenous to North America, making it possible to find a native aster perfectly suited to your landscape no matter where you live in the United States. Certain of these hardy, sun-loving perennials easily endure summer’s heat and then burst into or stay in bloom come fall, transforming a tired, washed-out garden with vibrant color.
“Asters certainly fill the bill when it comes to fall color,” says Allan M. Armitage, professor of horticulture at the University of Georgia’s College of Agricultural and Environmental Sciences and author of “Armitage’s Native Plants for North American Gardens” (Timber Press, 2006).
“They create a magnificent autumn display with their striking flower heads, which come in a variety of colors, including lavender, blue, white and pink.”
If you want a strong floral presence well into the fall, asters are your best choice, agrees Ron Wik, nursery business director for the New England Wildflower Society. “Many asters flower until frost, and there are even some that will re-bloom afterwards if temperatures warm again,” he says.
Adding to the aster’s reputation as an excellent fall native is the fact that it is also wildlife-friendly. These prolific, colorful flowers provide a great nectar source for bees and other insects in the fall when nature’s summer bounty has passed. They are also one of the best perennial host plants for larval butterflies and moths, such as the pearl crescent butterfly (Phyciodes tharos).
“The aster’s attraction to native pollinators is definitely one of its best attributes,” says Wik. “The flowers are heavy with pollen, making them a great food source for bees. Once they go to seed, they also provide much-needed nourishment to birds. And the larger asters make a sturdy structure that can support birds’ nests and provide a great place for butterfly transformation.” The fluffy seeds of asters also are used by a variety of birds to build nests.
Asters are highly adaptable, and many selections tolerate a wide range of conditions, says Steve Castorani, founder of North Creek Nurseries in Landenberg, Pennsylvania. His company, which has propagated asters since it opened in 1988, grows and markets many native plants for nurseries, wholesale growers, public gardens and conservation organizations. “There is an aster for almost every landscape,” he says.
Asters are the backbone of the natural meadow, contributing a variety of colors and heights, adds Castorani. “By combining many species, you can get them to bloom over a two- to three-month period in the fall months,” he says.
In general, asters are full-sun plants, requiring at least six hours of direct light a day. There are, however, some shade asters to choose from as well. “The white woodland aster (Eurybia divaricata) is a terrific ground cover and is especially valuable because it grows so well in dry shade,” says Castorani. “It has thin, nearly black stems that are topped with clouds of white flowers in early fall.” Symphyotrichum cordifolium is another selection that also thrives in dry shade.
In the home garden, asters can be used in massed naturalistic plantings, front or back of borders, full sun gardens, and prairie plantings, says Dr. Leonard Perry, extension professor at the University of Vermont and founder of perrysperennials.info.
Asters have thick, woody stems and long, narrow alternate leaves and many flower heads. Almost all are upright plants, although there are a few ground huggers and one that climbs. They come in a wide variety of sizes, from 4-inch-high creeping alpine varieties that grow naturally in rock crevasses to large, rambling plants covering vast meadows. Flower head size also can vary, from tiny to the size of a 50-cent piece. The New England aster (Symphyotrichum novae-angliae) grows 5 to 6 feet in height and boasts violet-purple flower heads with yellow centers. On the other end of the spectrum is Symphyotrichum ericoides `Snow Flurry,’ a plant that reaches just 6 to 8 inches tall, with ½-inch single white flower heads that give a billowy appearance. The latter aster can be grown as a ground cover and works well in rock gardens.
There are even asters that branch horizontally, like Symphyotrichum lateriflorum var. horizontale, which is a favorite of Perry’s. “This aster branches horizontally and to just 2 feet tall and has a delicate, understated, elegant effect,” he says.
For those gardeners who include asters in their native landscape, the good news is that they are extremely easy to grow. “Few flowers are as low-maintenance as asters,” says Armitage.
Sun asters ideally should be planted in a southern exposure, although they often do well in a western or eastern location. Place shade asters where they will receive dappled sunlight or morning sun. Asters can grow in clay or sandy soils but tend to thrive when organic matter is high and drainage is good. Fairly deep-rooted, they are drought-tolerant once established. They require little to no feeding, generally only needing an application of an organic fertilizer such as a 5-3-4 or similar once a year, says Perry, who notes that fertilizing heavily will lead to excessive foliage and few flowers.
Perhaps the best advice for growing healthy, abundantly flowering asters is cutting them back and providing enough space between plants to help them better resist disease. “With just about every aster, I would suggest pruning them about a month after they’ve started growing,” says Armitage, who notes that in Georgia he does this by June 1.
“Take garden shears and bring them down to a foot in height [depending upon the species],” he says. “There is no special procedure; I simply grab handfuls and cut them. This rigorous haircut will make them branch out and get bushier instead of growing tall and lanky.” If you don’t prune asters, they often will need to be staked mid-season.
Asters form large clumps and need to be divided every three years or so. At the beginning of the vegetative growth season in early spring, simply dig up the clumps and separate them at the crown into two or three parts, which you will then replant. Depending upon the variety, space asters 1 to 3 feet apart. You also can propagate them by softwood cuttings in the early summer, according to Perry.
Although asters have few problems, they are susceptible to rust and mildew. This is especially common in crowded, wet environments. Avoid these issues by providing enough sunlight and good air circulation.
Despite their obvious benefits and ease of growth, asters are sometimes the forgotten flower. “Because they are late-blooming, I think the casual gardener often misses them during the spring gardening season,” says Castorani. “Although we grow a wide variety of asters, there was a time when we offered even more. Aster sales are currently increasing slightly, but that hasn’t always been the case. We have had to limit our selection in the past.”
Sometimes mums win out for fall color, but asters are a better choice, agrees Wik. “Whereas mums are weak and often don’t survive for long, asters are truly perennial, making great foundation plants,” he says.
Wik grew up in Michigan, where fields of native asters are plentiful and admits to taking asters for granted as a child. “They were so common every fall that they didn’t seem that special to me at the time,” he says. “Today, though, I realize how garden-worthy they truly are. They really add pizzazz to the fall native landscape.”
Julie Bawden Davis is a California-based master gardener and author of books about gardening.