In the Garden:
The flowers of 'Bluebird' smooth aster and 'Fireworks' goldenrod mirror the colors of fall sunshine and a cloudless autumn sky.
Asters -- Love 'Em and Leave 'Em
A few weeks ago, as I was taking a walk through a old field on a beautiful, blue-sky fall day, I came upon an amazing sight. In among the tawny grasses and sunny sprays of goldenrod rose the pinks and purples of wild New England asters. And on one plant were clustered at least half a dozen monarch butterflies, busy fortifying themselves on the blossoms for their long migration to come. The vivid orange and black of the butterfly wings against the bright purple flowers was an arresting sight.
Which reminded me why I love asters and always include them in my garden. But I have a love/hate relationship with these plants, and I frequently find myself wondering why I continue to cultivate them -- or at least some of them. For while the flowers of asters are lovely, the plants (or at least the plants as I grow them) are often considerably less so. 'Alma Potschke', a New England aster cultivar that went to finishing school in Europe, displays its cheerful cherry-red blossoms beginning in mid-September in my garden. But it also displays its raggedy "bare knees" by the time it comes into bloom -- not a big deal in a wild setting, but not so appealing in a more manicured garden setting.
The lower-growing New York aster and its hybrids seem to be especially susceptible to powdery mildew. I used to grow 'Professor Kippenburg' with its lovely, light lavender blossoms. It was like the little girl with the curl in the old nursery rhyme. When it was good it was very, very good -- but too often it was just a mass of mildewed leaves. Eventually I consigned it to the compost pile. According to research done at the University of Vermont, regular sprays of horticultural oil beginning in late June are effective at combating mildew on asters, but that's too much work for me!
I have to point out that, botanically, most of my asters aren't even asters anymore. Those pesky taxonomists have been at work changing names again, and now, botanically speaking, the genus Aster is correct only for Old World species. So my tall New England asters have become Symphyotrichum novae-angliae and my New York asters, also called Michaelmas daisies, are S. novi-belgii. Plant catalogs and references may be updated or use the older, more familiar names.
But as I said, it's a love/hate relationship, and there are asters to love as well. I have had good luck with the New England aster 'Purple Dome'. This cultivar reaches only about 18 inches tall, short for this species, and seems to do a better job of hanging on to its lower foliage. The large flowers are a stunning deep purple and continue into late fall. When I have grown it under somewhat trying conditions of poor, dry soil, it has suffered from lacebugs, the insect most likely to trouble asters in our region. But these sucking insects are not usually a problem when I've grown it in a less hot and dry location. For severe lacebug infestations, insecticidal soap, neem, or spinosad sprays are effective, low-toxicity controls.
One of my favorite asters is 'Bluebird' smooth aster (formerly Aster laevis, now Symphyotrichum laeve). Coming into bloom toward the end of September in my garden, this aptly named cultivar has small, deep sky-blue flowers in profusion on a self-supporting plant that gets 3-4 feet tall and whose foliage is never marred by insects or disease. It makes an eye-catching sight blooming alongside the yellow sprays of 'Fireworks' goldenrod (Solidago rugosa) in my fall garden.
An earlier bloomer that I adore is Frikart's aster (Aster x frikartii). I grow the cultivar 'Wonder of Staffa', which is similar to, but a little taller than the other widely available cultivar, 'Monch'. Listed as growing 2-3 feet tall, it's on the shorter end in my garden, where its soft lavender flowers that begin to open in late July look lovely with 'Star Gazer' lilies and soft yellow daylilies in August and continue until mid-fall, where they accent mums and the tiny white flowers and purple-tinged foliage of Eupatorium rugosum 'Chocolate'. While Frikart's aster is listed as hardy only to Zone 5, mine has done fine with no special protection (other than waiting until spring to cut it back) in Zone 4 for many years. Mine has also been free from insect or disease problems.
And finally, I've come to love the low-growing 'Woods' aster (Symphyotrichum dumosum). Available in purple, blue, or pink cultivars, this diminutive aster is usually problem-free, reaching a mere 8-12 inches tall and spreading to form a carpet of color in the late-season garden. I've planted 'Woods Purple' near the late-blooming Allium thunbergii 'Ozawa', where its purple flowers with yellow centers provide a nice contrast to the spiky foliage and rosy flowers of the ornamental onion.
All of these asters will do best in full sun and in a spot with good air circulation. Most perform best if divided in spring every two to three years. Pinching or cutting back in early summer can help reduce the need for staking tall varieties. Rich, moist, well-drained soil that is high in organic matter will keep them happiest -- and if I gave all my asters such ideal conditions, I'd probably only have a love/love relationship with them!
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