Tried And True

Now there's help in finding asters that last

NEVER MIND all the new coneflowers and rudbeckias. Asters remain the archetypal late-summer daisies. Sure, they flop and need dividing regularly, but they bloom over many weeks in glorious shades that play off all the colors of autumn. So when I heard that the Chicago Botanic Garden was doing a multi-year trial to determine the best asters, I called up Richard Hawke, their plant-evaluation manager, to learn the results.

The Chicago Botanic Garden has been evaluating plants for their garden-worthiness since 1985, and asters are the largest trial group ever. Hawke started out wondering why only a handful of asters are widely grown when so many species and cultivars are out there. So he gathered 150 kinds and planted them in circular beds. Similar flower colors are planted side-by-side to more easily judge the various shades. His team will watch the asters closely for five to six years (all perennial trials last at least four years). Now, halfway through, he's pretty sure he's got the answer: "There's just a handful that are really good."

"I struggle to make it as scientific as possible," he says of the judging. To this end, he's established 28 criteria that include flower size, growth habit, winter hardiness and disease resistance. Cultural adaptability is the most important of all, because the asters need to thrive in the display garden's windy, full-sun conditions. Since our summers are less muggy and our winters warmer than Chicago, you can figure that any aster that does well there will grow happily in Seattle.

Hawke has been disheartened by the floppiness and mildew that all too many of the asters exhibit. But he cautions against making up your mind about a plant too soon. "So often I learn more over the years" as the plant changes, he says. "The top performers sometimes aren't the ones I'd expect." He's jaded about all the new plants introduced every spring. "Who knows what we'll learn about their garden-worthiness in three or four years?" Although he's already vetted out more asters than anticipated, he still thinks many are adaptable plants that deserve better than being "relegated to roadside status."

I ask Hawke about my favorite watermelon-pink aster, 'Alma Potschke.' He agrees its hot-pink color puts on quite a show under autumn skies, but regretfully reports that Alma probably won't make the list for its sprawly ways and mildew-prone foliage. Three years into the trial, these asters have definitely made the cut:

• Hawke's favorite so far is A. tongolensis 'Wartburgstern,' which he deems "a phenomenal little plant." An early bloomer, it has rosettes of violet-blue flowers on sturdy stems, is a good cut flower, has an open growth habit and reaches only about a foot in height. No staking needed.

• A. ericoides prostratus 'Snow Flurry' is also a groundcover aster, with wiry dark stems and tiny white flowers perfect for cascading down a wall or hillside. "That thing is covered with flowers," marvels Hawke. I planted it in my old garden around the base of a eucalyptus, where it mounded up and bloomed profusely from July through frost.

• A. tataricus 'Jin-dai' is a more traditional-looking aster, with handsome, coarse foliage and a full habit. Its pretty lavender flowers are centered in yellow. Although it reaches 4 feet, it's so sturdy it doesn't need staking.

• A. oblongifolius 'Raydon's Favorite' has foliage with a fruity fragrance, grows 3 to 4 feet tall and wide, and is covered with dark lavender flowers. It looks like one of the traditional New England asters, so is right at home in a cottage garden or planted in drifts with other late-blooming perennials.

Valerie Easton is a Seattle freelance writer and contributing editor for Horticulture magazine. Her e-mail address is valeaston@comcast.net.