Amazing Asters

Asters are to monarchs what krill are to whales.GN-MPF Logo PDF_CMYK

By Scott Woodbury

For millennia monarchs and whales have honed migration routes over great distances and through historic feeding grounds in order to accomplish one basic thing: produce offspring. Monarch butterflies in the central United States followed a vast ribbon of tallgrass prairie and savanna full of asters that once stretched from Canada to Texas. Like ancient celestial clockwork, migration of adult monarchs commences with the first aster blossoms in August and ends in early October.

Unfortunately, original prairie and savanna today exists in scattered patches, in preserves, some land owned by private individuals, railroad corridors, and roadside edges. It’s hardly a monarch buffet because monarchs need lots of asters, much like whales need tons of krill. One does not exist without the other, which explains why whales and monarchs are in trouble. I wish we could make more krill, but we can make more asters. We can buy them and plant them at home. We can encourage their use in city parks and at churches. We can tell friends and neighbors this amazing monarch and aster story and about the natural history of the prairie and savanna. There are things we can still do to make our world better.

Aromatic aster with skipper sw

Aromatic aster with skipper

In late summer and fall, flowering asters brim with nectar, the sweet food that fuels monarch migration. True, there are other plants like goldenrod and blazingstar (close relatives to aster) that feed hungry monarchs, but none are as ubiquitous as asters. For better or worse, the genus name for most asters is now referred to scientifically as Symphyotrichum—so much for a modern progression toward more user-friendly devices.

First to bloom is purple aster (Symphyotrichum (Aster) patens) in late August when monarch migration begins. Clump-forming purple aster grows in dry prairies and savannas, so it is a good choice for landscaping in part shade and dry slopes. Next is southern prairie aster (Eurybia (Aster) hemispherica), a sun-loving prairie plant that slowly spreads into small colonies with large purple flowers. New England aster (Symphyotrichum novae-angliae) blooms in August and September, is tall, and a little weedy in gardens. Still it is one of the best aster species for butterflies. Ditto for its big-bro, the glossy-leaved aster (Symphyotrichum puniceum).

New England aster sw

New England aster

During peak migration, sky-blue aster (Symphyotrichum oolentangiense) and smooth aster (Symphyotrichum laeve)—both blue-flowering asters—are in bloom. Deadhead sky-blue aster because it spreads aggressively from seed. Smooth aster grows best on well-drained soils. I would welcome it to spread from seed if it could, but it is a shy performer when you don’t have rocky soil. Last year I observed eighteen monarchs on a small patch of willowleaf aster (Symphyotrichum praealtum) in my yard. I think society would do well to follow suit with a willowleaf aster in every park, church, and cemetery from Canada to Texas. Want less grass to mow? Plant a little patch of willowleaf aster. Yes, this is a suckering perennial that spreads quickly in full sun and poorly drained soil, but this aster forms dense, low-maintenance colonies that are easily kept in place in the middle of mowed grass.

At the tail-end of monarch migration, aromatic aster (Symphyotrichum oblongifolium), comes into bloom. Because there are few other plants blooming in October and early November, it is an insect magnet. Not so many monarchs, but plenty of skippers, moths, bees and wasps find their last taste of nectar there. Every lover of asters and garden insects should have one. It is low-growing, topping out at two to three feet, depending on soil fertility. They are mounded and make excellent perennial hedges.

willowleaf aster sw

Willowleaf aster

When I wrote that asters are ubiquitous, I meant that some of them show up everywhere. Commonly referred to as DWAs—short for “darn” white asters, because they are hard to tell apart—these plants are a nuisance in most gardens and farm fields. Their seeds spread on the wind, sprout everywhere, and rapidly grow into flowering plants in a single season. This group of asters is in part why north St. Louis has remarkably high bee diversity (160 plus species), greater than any other known Midwestern city according to Gerardo Camillo, biology professor at St. Louis University.

Of the 24 aster species, nine are white-flowering and not typically cultivated because they spread aggressively from seed. Of those nine, white heath aster (Symphyotrichum pilosum) is the most common and weedy. It has hairy stems and leaves with flowers that smell like butterscotch and is clump-forming. I weed out all but a few in the garden, leaving some because they smell so nice and are  awesome pollinator plants, especially for monarchs.

Urban decline is a mixed box of chocolates. The best chocolate lies in the resiliency of native asters and the insects they attract. Most cities have them, neighborhoods in transition. A hundred years ago they thrived with people. Today they thrive with wildlife and with your help with planting showy native asters, they can be beautiful as well.


Horticulturist Scott Woodbury is the Curator of the Whitmire Wildflower Garden at Shaw Nature Reserve in Gray Summit, MO, where he has worked with native plant propagation, design, and education for 25 years. He also is an advisor to the Missouri Prairie Foundation’s Grow Native! program.

Photos courtesy of Scott Woodbury.

 

 

 

 

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