(Author’s Note: The following article is excerpted from my upcoming book, The New England Gardener’s Year. The book is scheduled to be published as an e-book later this year (November) and in print version early next year (February). To see more photographs of the herbaceous perennials discussed in this article, visit the The New England Gardener’s Year Facebook page, http://www.facebook.com/negardener).
There are several herbaceous perennials that belong in the October garden. Some, like the heleniums, begin flowering as early as August and continue into autumn, while others wait until late September or early October to burst into bloom.
Smooth Blue Aster (Symphyotrichum laeve)
The smooth blue aster is a native fall-flowering plant throughout New England. It grows 2 to 3 feet tall with a central stem that produces a few flowering side shoots in its upper half. Each flowering stem produces panicles of numerous daisy-like flower heads, each about 1/2 to 1 1/4 inches across. Like most members of the sunflower family, each head has about 15 to 30 lavender or light blue-violet ray flowers surrounding a disk of yellow flowers. These tiny central flowers turn reddish yellow as they age.
The common name, smooth blue aster, reflects the lack of hairs on the stem and leaves. Gardeners interested in planting smooth blue aster should look for the cultivar ‘Bluebird’, and improvement over the species.
Flowering begins in late September in Zone 5 and lasts 3-4 weeks. During October, the small fruits, called achenes, develop with small tufts of light brown hair that aid in dispersal by the wind.
Smooth blue aster has many attractive qualities including adaptability to a variety of soil types, beautiful flowers, attractive foliage, and stems that remain erect during the blooming season. It performs best in full or partial sun, and mesic soils, typically fertile loam or clay loam. Plants withstand drought fairly well.
The flowers of smooth blue aster provide much needed nectar for monarch butterflies about to embark on their long flight. They also attract native bees, syrphid flies, and hoverflies. The caterpillars of the silvery checkerspot butterfly feed on the foliage, along with caterpillars of many moth species.
Swamp milkweed (Asclepias incarnata)
By October, caterpillars of the monarch butterfly are munching on the leaves of swamp milkweed as the first ripe seed capsules are splitting open to release their seeds to the wind. Silky hairs at the end of each seed form a parachute-like tuft that aids in dispersal.
Swamp milkweed is a tall plant with fragrant clusters of pink and light purple flowers. As its name implies, it prefers moist to wet soils and is ideal for planting in the rain garden or along the edge of a pond. Best grown in full sun, it tolerates heavy clay soils and is very deer-resistant.
Stonecrop (Hylotelephium spectabile)
Known by several common names, including showy stonecrop, showy orpine, ice plant, and butterfly stone crop, this plant (formerly named Sedum spectabile) is Asian in origin but has escaped cultivation to become naturalized in small areas of Connecticut and Massachusetts. It has an upright habit, reaching 18 inches in height and width with leaves that are bluish-green and semi-succulent. Clusters of pink flowers open in late summer and last until frost. A hybrid between this species and S. telephium led to the introduction of the very popular cultivar, ‘Autumn Joy’.
Stonecrops should be grown in full sun and well-drained, neutral to slightly alkaline soil that has been amended with plenty of compost. Divide the clumps every 3 or 4 years. Plants often flop late in the season and may need staking.
Beautiful in the October border, stonecrop is very popular among bees as a source of late-season nectar.
Sneezeweed (Helenium autumnale)
Helenium autumnale, common sneezeweed or dog-tooth daisy, occurs in wet meadows, thickets, swamps, and river margins throughout New England. Garden forms of this species also show a preference for damp conditions, although they will tolerate all but the driest of soils. They can be grown on heavy clay that is annually amended with compost.
Cultivated forms of Helenium autumnale can be found in a wide array of rich colors from pale yellow to deep red and bronze.
Giant Sunflower (Helianthus giganteus)
Native throughout New England, the giant sunflower lives up to its name, reaching 12 feet in height when grown in rich garden soil. Without sturdy staking you will go to the garden the morning after an October storm and find some of its tall stems lying on the ground. Not a candidate for the perennial border, it is better suited to stand alone at pond’s edge or where woods and clearing meet.
Giant sunflower is not particular about soil type, growing well in sandy, loamy, or clayey soils as long as they are well-drained. It is cold hardy to USDA Zone 4.
The flower heads are borne on numerous leafy branches in the top third of the main stem, each head measuring 2 to 3 inches across. The first heads appear in late September, but the main show is reserved until October.
Given its size and tendency to be flattened by wind, what gardener would grow this mammoth plant? Anyone interested in attracting wildlife, for sure. The nectar and pollen of the flower heads attract bumblebees, hoverflies, butterflies, and other pollinators. Other insects feed on the foliage and stalks, including numerous species of beetles as well as caterpillars of the silvery checkerspot and painted lady butterflies. The seeds are eaten by mourning doves, white-winged crossbills, goldfinches, black-capped chickadees, white-breasted nuthatches, tufted titmice, and various sparrows.