September brings the end of the flowering season as fall arrives in native plant gardens. A few flowers may linger into October, but this month is a good time to harvest mature seeds on summer-blooming species. Other tasks include weeding, trimming, and noting changes to make the coming year. We are preparing for our annual Native Gardening Conference, to be held on September 18. The garden is featured in tours and several workshops. Conference registration is full.
My least favorite part of the fall garden transition is saying goodbye to the student garden assistants as they return to school. Kymberly and Emma have learned many native plants, documented bumble bees, hauled many loads of weeds, put up with heat and chiggers, spotted interesting insects and birds, enjoyed working with our garden volunteers, and more. Thank you, Kymberly and Emma!
Throughout August and September, warm-season grasses and members of the sunflower family (Asteraceae) are abundant in our prairie and rain (wetland) gardens. Some shade-tolerant species of the sunflower family, such as Short’s aster (Symphyotrichum shortii) and elm-leaved goldenrod (Solidago ulmifolia) are still blooming in savannas and woodlands. New England aster (Symphyotrichum novae-angliae) is common in dry to wet-mesic sites with full sun. A tall plant, it continues to bloom and set seed through September and October. The flower color can vary from pale pink to dark red-purple to purple. It is one of the last asters in bloom throughout September.
Many grasses, asters, and goldenrods have wind-dispersed seeds. This explains their success in spreading throughout the garden. Some, like Canada goldenrod (Solidago canadensis) and flat-topped aster (Doellingeria umbellata), also have extensive rhizomes (underground stems growing horizontally), allowing them to spread vegetatively.
The latest blooming asters begin flowering in September. They are found in our lime prairie, parking circle, sand prairie, dry-mesic prairie, and mesic prairie gardens. The aromatic aster (Symphyotrichum oblongifolium) is highly branched, and about 1 to 2 feet tall. It has small, narrow, alternate leaves and flower buds bearing tiny glands that give rise to the distinctive scent of the plant. The flower heads are purple, relatively large (1 inch in diameter), with more than 20 ray flowers on each head. It requires open sites where it will not experience competition. The root system is fibrous and rhizomatous; each plant can expand, covering more area. It is a late-season nectar source for bees and butterflies, and a larval host of butterflies and moths.
Heath aster (Symphyotrichum ericoides) is another rhizomatous plant, which also spreads readily by seed. It grows to 2 feet tall, has small linear leaves and small tightly clustered white flower heads (less than a half-inch in diameter). It grows well in full sun in dry conditions and withstands drought. A wide variety of bees, flies, and wasps visit the flowers, and the leaves and stems provide food for lace bugs, plant bugs, and aphids, as well as larvae of several moth species.
Silky aster (Symphyotrichum sericeum) is the shortest aster in this group, growing to only 6 to 18 inches tall. It thrives in open sites and is drought tolerant. The stems are wiry, and the leaves are oblong to elliptical and covered with soft hairs. The lavender-to-purple flower heads are showy, with 10 to 22 ray flowers on each. The flower heads are one inch across and attract bees, flies, and small butterflies. The foliage is eaten by larvae of many species and by other adult insects.
These three asters would be suitable for rock or gravel gardens and dry exposed sites, where they can avoid competition and disperse seed onto bare soil. They are beautiful, relatively small, attractive, and ecologically valuable late in the growing season.
—Susan Carpenter, Native Plant Garden curator