If you’ve wandered by a native aster on a crisp autumn afternoon while the sun warms your back, then you’ve seen what this plant does for local wildlife, especially pollinating insects and bugs. From a distance, it may seem like asters are the center of a snow globe as the glittering, delicate bodies of flies, bees and beneficial wasps rise and then settle again over the flowers.
Scientific studies show precipitous insect decline, which behooves gardeners to not only be aware of the issues facing pollinators but how we can be part of the answer. Providing as many resources as possible for adult and larval-stage insects and bugs is one way to help. Another way is creating awareness in our communities by displaying stunning plants loaded with pollinators. Asters fit the bill on both counts.
Native aster species provide shallow blooms that make for easy pollinator landing pads, and with the large number of available florets filled with food, an insect can hang out longer while feeding and conserve energy. Male bees are often seen refueling on asters before they continue their search for a female. Various flies, such as bee and syrphid, will visit, alongside soldier and other beetles. The specialist arcigera flower moth caterpillar feeds on aster blooms and seeds, then overwinters as a pupae in the soil, emerging as an adult in late summer to mate and begin the cycle again. Pearl crescent and silvery checkerspots also use asters as a host plant.
Pollinator support goes hand in hand with beauty for us. As a group, asters provide a succession of blooms that lasts from the first big-leaved asters flowering in late summer to the aromatic asters still blooming in mid- to late autumn.
What’s in a Name?
Now before we go any further, it’s important to note that asters aren’t Aster anymore. Most are now officially called Symphyotrichum pronounced sim-fie-oh-TRICK-um or sim-fee-oh-TRY-kum. Aster is an old-world genus name coming from the Greek “astron,” which means star. There used to be about 180 North American plants in the genus whose flowers looked starlike. But with advances in DNA research, we’ve seen that just because plants look alike doesn’t mean they are closely related. So now an aster could be Symphyotrichum, Eurybia, Baccharis, Ericameria, Solidago and more. The benefit of this Latin chaos? We can better understand how plants interact with their ecosystems and effectively track the rise or decline of species.
Regardless, we’re going to look at a few native aster species as “asters,” focusing on Symphyotrichum species, which thrive in most cultivated garden settings. With the exception of smooth aster, they are all hardy to USDA Zone 3. Here are six native asters that provide blooms and pollinator food from August until October or beyond.
Smooth Aster (Symphyotrichum leave)
Perhaps the most adaptable native aster on this list, smooth aster does well in full to part sun with medium moisture, in everything from loamy clay, to clay, to loamy sand soil. It will bloom in late summer to the middle of fall with blue to violet flowers atop 2- to 3-foot stems with moderate branching toward the top. As you might have guessed, the leaves are very smooth with a blue-green tint. Plants are 2 feet wide on average, and the autumn color is yellow to red. In open soil or a bed dominated by wood mulch, self-seeding can be moderate. In a dense planting, you’ll only find a few seedlings, year to year. Hardy to zone 4.
Sky Blue Aster, Azure Aster (Symphyotrichum oolentangiense)
If you enjoy the general form, size and bloom color of smooth aster but have a really hot, dry, sunny site, then this is the native aster for you. It’s a bit more airy and open in structure, and still moderately branched at the top, but it will thrive in well-drained sandy, rocky, clay or loam soil that gets all the summer and autumn heat.
Heart-Leaved Aster, Blue Wood Aster (Symphyotrichum cordifolium)
There are plenty of woodland aster choices, and while more sun will mean more blooms for heart-leaved aster, you’ll still get the color you’re looking for in a shady, dappled sun or woodland edge garden. Reaching roughly 2 to 3 feet tall and 1 to 2 feet wide, this aster does best in medium moisture soils with decent organic matter, think loam to loamy clay. Can you guess what shape the leaves resemble?
Calico Aster (Symphyotrichum lateriflorum)
The center of each bloom on this aster turns from yellow to pink when the nectar supply is exhausted. Those nectar tubes are shorter than many other asters so you’ll see a great diversity of short-tongued pollinators visit. Calico aster is a go-to deep-shade to part-shade perennial with hundreds of small white flowers with wiry, bushy tops and slender legs. With ample moisture, it can get 3-by-3 feet in size, and 2-by-2 feet in medium to dry sites. The leaves are small and thin and, given its leggy nature, underplanting with sedge or a thicker native groundcover might be ideal.
Aromatic Aster (Symphyotrichum oblongifolium)
Asters are absolutely critical to late-season and migrating pollinators, which is why having a succession of them is so important. Some years, I see a few straggling pollinators coming by after a hard frost or two, and aromatic aster keeps the blooms coming once the warm afternoon sun hits the garden. This is a tough, slowly spreading, shrublike aster that reaches 2 feet tall and 3 feet wide when moisture is ample, slightly smaller when it’s not. Aromatic aster tolerates drought and prefers full sun and medium to well-drained soils. The flower color ranges from magenta to violet blue, while the seeds hold on most of the winter, entertaining humans and feeding wildlife.
Big Leaf Aster (Eurybia macrophylla)
This might be the groundcover you’re looking for in a shady to part-shade site around leggy calico aster. The oversized leaves tend to reach no more than about a foot tall. In late summer, the flower stalks go another foot beyond that but with a smaller number of white blooms than other asters on this list. It will bloom in late summer, probably just before calico aster, and in a loamy soil it will spread moderately by rhizomes (lesser so in clay). If you have a shady area you don’t know what to do with, let this aster do its thing.
Now that fall is here, stop to take a deeper look at the massive variety of aster-ish asters North America provides—your garden and the pollinators coming through will be the richer for it.
This article by Benjamin Vogt originally appeared in the September/October 2019 issue of Northern Gardener. He is the author of A New Garden Ethic (New Society Publishers, 2017) and a garden designer in Lincoln, Neb.