Wildflowers have long presented a quandary for gardeners. Their natural purity is sometimes too pure. The stems are weak, the flowers are small and fleeting, and the plants often melt away with excessive coddling.

Enter plant hybridizers, patient and ever ready to fix weaknesses and to appeal to the gardener’s lust for showier flowers in new colors.

One sun-loving prairie plant you might think needs little of all that breeder’s attention would be the purple coneflower Echinacea purpurea. With its robust, daisylike blooms of pink-purple petals and orange centers, or discs, it provides a great show for a month or more beginning in mid-June. In July, the discs elongate into cones.

The coneflower aligns itself perfectly with modern gardening sensibilities: It is native, tough and long-blooming, and it sustains butterflies and bees. By late summer, the seed heads draw goldfinches. It stays decorative even in its faded state.

What’s the catch?

Coneflowers are not long-lived perennials. They can peter out after two or three years, especially in beds where they don’t get the drainage they need. Excessive mulches, heavy clay soil and irrigation systems work against them.

A few years ago, breeders discovered they could cross the purple coneflower with other coneflower species and produce hybrids in alluring colors: highly saturated pastel shades of raspberry, orange, lemon or apricot. Gardeners went mad for them, but most of these hybrids gave up the ghost even faster than their wild cousins.

Still, the new varieties come thick and fast. Some seek to address the longevity issue, others are compact for small gardens, and some lose the daisy in favor of a pompon of double flowers. The unnatural but enticing flower colors continue.

Some of these new varieties have petals that spread horizontally. In others, they grow downward, and these reflexed petals bestow a different but agreeable characteristic to the flower.

In light of this, the horticulturists at the Mt. Cuba Center botanical garden near Wilmington, Del., decided to revisit the coneflower with a rigorous, three-year trial of Echinacea that ended last year. They evaluated 75 varieties, hybrids and species, assessing such traits as length and abundance of bloom, general vigor and foliage ornament.

The coneflower trial updated another evaluation held more than a decade earlier. Two varieties that fared well the first time around were winners again: a compact, free-flowering variety named Pica Bella and a white-flowering version named Fragrant Angel, with big blooms. Pica Bella was the highest-scoring in both trials, which is remarkable, given the flood of new varieties over the past decade.

“It held up against all this new breeding,” said Sam Hoadley, manager of horticultural research. In addition, both Pica Bella and Fragrant Angel were among five of the top dozen that also rated as top pollinator attracters. The others were Glowing Dream, with luminous tropical pink blooms; Postman, with showy dark cones and petals that age from crimson to watermelon pink; and Sensation Pink, with neon pink blooms, dark stems and a desirable compact habit. Coneflowers planted in rich soil can grow four to five feet and begin to flop.

Several of the intensely colored coneflowers also ranked highly, including the low-growing, coral red Santa Fe; the raspberry pink Raspberry; and the red-orange Intense Orange, the last two from a series named Kismet. When I visited Mt. Cuba in September, I found this variety growing happily and to great effect in a container.

The oddest variety, and also a top scorer, was Snow Cone, whose white, deeply reflexed blooms are small for a coneflower, but massed in a profusion that masks the foliage. At little more than two feet tall, Snow Cone would work in a container or at the front of a border, the evaluators say.

As for gauging the true perennial nature of coneflowers, 13 percent of the varieties didn’t make the three years, and most of those died after just one season. One stumbling block was the prevalence of a disease named aster yellows, which killed almost a quarter of all the plants in the trial and interfered with the long-term evaluation. Hoadley said the trial garden was probably unusually prone to the disease because of the concentration of aster-family plants grown there over a long period, including coneflowers.

My own taste doesn’t run to the fancy-colored coneflowers; I like my purple coneflowers close to the species form — I grew Magnus for years, a reliable performer — and let the seedlings perpetuate the display.

I also like two other species, but they are even fussier about having lean and free-draining soil. One is the Tennessee purple coneflower (Echinacea tennesseensis), whose pale pink petals radiate but do not overlap. The other is the pale purple coneflower (E. pallida), whose long, ribbonlike petals hang down. A variety named Hula Dancer outperformed the species in Hoadley’s trial.

The trial also confirmed what gardeners already sort of know: Double-flowered blooms are of little value to bees, butterflies and other desired pollinators. The flower structures have mutated to a point where the rewards of pollen and nectar are reduced or absent.

“It’s good to have those suspicions confirmed with real observations,” Hoadley said.

Tip of the Week

Birdhouses should be examined before nesting season to ensure they are secure, clean and free of mice nests. Entrance holes enlarged by undesirable species can be fixed using metal plates sized for smaller birds, such as wrens and chickadees.

— Adrian Higgins

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