By Debra Knapke
Autumn is the time of golden, scarlet, and maroon leaves and shortened days. It is the time for picking apples and harvesting vegetables. We watch our gardens slowly decline, and yet there is one perennial that says “Wait, my time is now!” Enter the asters, the late summer to fall-blooming plants so loved by bees and butterflies.
We often overlook the flowers of autumn as we fill out our gardens with spring and summer blooms. Many of us buy plants in April, May and June when the spring and summer flowering plants proudly show their colors. But we overlook the asters which are just emerging: green leaves and no flowers.
Asters are not difficult to grow. Here are a few cultivation and maintenance guidelines:
- Asters prefer full sun, 6+ hours of light; most tolerate part sun, four to five hours of light.
- Most asters are drought-tolerant if you keep the soil moist during the first year in the garden.
- Asters love compost, but excessive fertilization will cause them to grow quickly and ungainly; an aster lying on the ground is not attractive!
- The taller asters should be cut back by 1/3 in early to mid-June to promote stronger stems and to avoid the need for staking.
- Asters are best divided in the spring.
It’s not too late to add these late bloomers to your garden, but don’t wait too long. After late August, asters may not have enough time to grow their roots into the soil and acclimate to your garden before winter arrives. If you miss the planting window this year, buy the green, leafy aster next spring.
Here are some species that are native to most of the Midwest. Many of the cultivars listed have been selected for their compact habits and richly colored flowers.
- Aromatic aster (Symphyotrichum oblongifolium) – has aromatic foliage; height 18-36”, width 12-18”; blooms Sept. to Oct.; sky blue to lavender-blue flowers; Look for: ‘October Skies’ (compact: ht. 18”); ‘Raydon’s Favorite’
- Blue wood aster (Symphyotrichum cordifolium) – height 2-4’, width 2-3’; performs best in part sun, but tolerates sun to shady conditions, blooms Aug. to Sept.; small light blue flowers
- Heath aster (Symphyotrichum ericoides) – height 1-2’, width 12-18”; blooms Aug. to Oct.; white to light pink flowers; look for ‘Pink Cloud’ ‘Snow Flurry’: both are more compact selections
- New England aster (Symphyotrichum novae-angliae) – height 3-6’, width 2-3’; blooms Sept. to October; light lavender or pink to deep purple or pink flowers; if the soils dries out, this species will lose the lower leaves on their stems; look for: ‘Purple Dome’ (compact: 24-30” tall) ‘Vibrant Dome’ (compact: 18-24” tall) ‘September Ruby’
- Smooth aster (Symphyotrichum laeve) – height 2-4’, width 18-24”; blooms Sept. to Oct.; striking blue-violet flowers; look for: ‘Bluebird’
- White wood aster (Eurybia divaricata) – the exception: prefers part sun to full shade; height 12”, width 18-24”; bloom Aug. to Sept.; white flowers; ‘Eastern Star’ is a more compact selection
Side Note: The Aster Name
Not only do our native asters suffer because they lack early flowers, but they have been separated into new genera with difficult names. One of my horticulturist friends calls it the “aster disaster”. If a garden center has arranged the perennials by their botanical names, the asters will be spread across several locations on the nursery shelves. Fortunately, in most garden centers, asters still hold a place at the beginning of the alphabet instead of being scattered throughout the benches. For those who are interested the new botanical names are listed with the common names.