I spend all summer watching the asters in my garden grow larger and larger, their long stems arching over their black-eyed Susan and coneflower neighbors. For most of this time they are in the way and boring to look at. But when they hit their stride in September, all is forgiven. With their purple and white flowers standing in contrast to the golds, reds, and oranges of fall foliage, this native perennial becomes the star of my autumn garden.
And, oh, how the insects love them. They bloom just in time: Asters are a food source for many living creatures at the point when they are preparing for the coming winter. And not just food for pollinators such as bees, butterflies, and wasps, but birds who come to eat the bugs, but who also eat aster seeds.
Asters flowers look like tiny daisies so it’s no surprise that they are in the daisy family. Most asters are lavender or purple, but they also come in white, pink, blue, and red. Most aster species are native to North America, and there are dozens of cultivars.
The botanical name of some asters has changed. Where before they were simply Aster, they are now Symphyotrichum. You may see it on plant tags, but no worries, they are still sold as asters, so you don’t have to pronounce such a mouthful!
Asters are not difficult to grow. Plant in early to mid-spring in well-drained soil. Full sun is best, though they’ll take light shade. Too much shade yields fewer flowers. Fertile soil makes them lanky and floppy, so you might want to contain them in their own bed away from heavier feeders. You can also keep asters smaller and bushier by pinching them back by a third to a half in June. Don’t pinch after the beginning of July or you’ll take off the flower buds.
Keep them watered until plants become established. Asters like moist, though not consistently waterlogged soil. Too little water yields fewer flowers. Two or three inches of mulch around the plants helps hold in moisture.
Taller varieties should be staked to keep them from flopping.
Unfortunately asters can get powdery mildew, which looks like gray dust on the foliage and diminishes its attractiveness, though overall it doesn’t much harm the plant. Plant asters in full sun in an area with good airflow and they’ll be less likely to get mildew.
Asters spread by seed and by rhizomes. Deadheading plants gets rid of the self-seeding problem, but it also takes away a food source for birds. Better to pull out seedlings in the spring than to deadhead.
Native Aster Species
New York aster (Symphyotrichum novi-belgii)
Also called Michaelmas daisy, this species can take more moisture than other asters. Native species can vary in color from a blue-purple to light lavender to white. Grows 3-4’ tall, though cultivar heights vary. Hardy in USDA Plant Hardiness Zones 4 to 8. ‘Climax’ has lavender-blue flowers, a long bloom period and excellent disease resistance. The hybrid, Aster x frikartii ‘Moench’ has large, upright lavender flowers and grows only 2’ tall.
New England aster (S. novae-angliae)
Taller than New York aster, with an upright habit and hairy leaves. Varieties vary in height from 3 to 6’. Hardy in Zones 3-8. Native plants have purple flowers. ‘Alma Potschke’ with pink flowers, has good mildew resistance. ‘Harrington’s Pink’ is a profuse bloomer with rosy-pink flowers. The cultivar ‘Purple Dome’ is covered in violet-purple flowers.
Bushy aster (S. dumosum)
This aster is smaller than the others (1 to 3’), and is more mildew and rust-resistant. It is native to the northeastern U.S. Hardy in Zones 4 to 8. The variety 'Wood's Pink' has bright pink flowers; ‘Wood’s Light Blue’, pale blue flowers.
Smooth aster (S. laeve)
Another aster with good mildew resistance, smooth aster stays at a manageable size: 2’ to 3’ tall and 2’ to 2 ½’ wide, so it doesn’t need staking. It’s hardy in Zones 4 to 8. The variety ‘Bluebird’ has violet-blue flowers.
Asters are larval host plants for pearl crescents, silvery checkerspot and painted lady butterflies, as well as nectar plants for the adults. Butterflies that are attracted to the nectar include Gulf fritillary, sulphurs, and monarchs.
Because they can get leggy and lose their lower leaves before they bloom, the taller asters should be planted towards the back of the border, where their bare lower stems can be covered by other plants.
Asters’ big, billowy form is a perfect counterpoint to ornamental grasses. Their colors complement sedums, black-eyed Susans, echinacea, hydrangeas, and other late summer bloomers. And of course, they are a natural pairing with goldenrod (Solidago). Every garden needs at least one aster. The pollinators agree.
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By The Davey Tree Expert Company
Photographs courtesy of The Davey Tree Expert Company
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