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Late Summer's Perennial Spectacular

By Adrian Higgins
Thursday, August 27, 2009

As unpleasantly hot and humid as Washington can be in August, there are moments in the garden when it's actually quite agreeable. Find a breezy spot in the shade and take in the late-season lushness.

Tropical plants such as the various elephant ears and cannas are large and bold by now, and the ornamental grasses have not only reached their full girth but are in vibrant flower, bar the late-season miscanthus varieties. The most valuable components of the late-summer garden, however, are the perennials in bloom. Many of them are big plants, and they want to party.

Everyone knows the annual sunflower, but the related perennial sunflower is the one for grown-ups. Every sunny garden should have at least one, for there are several species and varieties. They grow to about eight feet, are freely branched and generous in bloom, and can flop a little. This adds to their charm.

I like the varieties of swamp sunflower (Helianthus angustifolia) that are more softly yellow than the norm. Lemon Queen is widely admired by serious gardeners for its clean creamy yellow petals around a central disk fluffed up by its tiny pollen-bearing anthers. Another great variety is Mellow Yellow, a little more buttery and with wine-colored stems. As their name suggests, swamp sunflowers like abundant moisture (and occasional feeding), but if you pamper them too much they will spread more than you want. The remedy is to grub out the babies.

Another agreeably lanky species is the hairy sunflower, Helianthus hirsutus, with daisies that are golden yellow. Bill McLaughlin of the U.S. Botanic Garden likes the dark-eye sunflower (Helianthus atrorubens), which is just starting its season. It is a shorter perennial, no taller than six feet, with rough leaves and a distinctive daisy, a strong yellow surrounding a red-brown center. "It really pops in a garden," he said, "it pairs well with Vernonia angustifolia." That plant is better known as ironweed, which is an attractive, violet-colored tall flowering native plant that can spread when happy. I await with excitement the mail order arrival of a shorter ironweed variety named Iron Butterfly, which is quite different in its feathery foliage and branching habit.

Speaking of feathery foliage, but on a much larger scale, the willow-leaf sunflower is a lax, sprawling plant whose buds are just swelling. In a couple of weeks, dozens of golden yellow flowers will illuminate the wispy stalks.

The giant coneflower, Rudbeckia maxima, is on the wane now, but another big coneflower still looks fabulous. The variety of Rudbeckia subtomentosa called Henry Eilers has tubular petals (quilled rays in garden-speak) that radiate from a central dark-brown disk. It is a most handsome coneflower, rising to six feet.

The goldenrod brightens the meadows of August, though the wildflower is too tall for most gardens, and it spreads. Many improved and better-behaved varieties are available, notably Fireworks, Crown of Rays and Golden Fleece.

The king of the August border is the common mallow, festooned with impossibly oversize blooms, some approaching a foot across. I saw the old variety Lord Baltimore the other day, a plant that had grown to eight feet with more than two dozen thick stalks emerging from its crown. It was full of ruffled, crimson red flowers playing in the breeze and crowded with many more buds, promising a display well into September.

The swamp mallow, Hibiscus coccineus, is dainty by comparison; the red petals don't overlap and so create wonderfully conspicuous stars about four inches across.

At the Botanic Garden, I came across a white form of this that was one of those plants you just had to have. It was tall, to nine feet, but upright and loaded with creamy white blossoms with a hint of green. The blooms, held aloft, are backlit and magical. It is sometimes rare at this point of the summer to find perennials that still look fresh, but here is a plant that not only is clean but also has stems with a bluish cast to them. As McLaughlin points out, "the whole effect is cool" in a sweltering month. He grew it from seed, but it may be identical to one in the nursery trade called Summer Snow.

If you haven't the space for sprawling giants, smaller but highly attractive perennials offer a lot in late summer. One of the cutest native plants is the American senna, an herbaceous legume that grows to about four feet and is covered in clusters of yellow pealike flowers against which the conspicuously black anthers form a speckling. "It's a great, statuesque plant typically from wetter areas," said McLaughlin, "but [is] deep rooted and can take incredible dryness."

I also came across a diminutive Joe Pye weed species named Eupatorium dubium. It grows to just four feet and is smothered in mauve flower heads on upright stems. It looked neither ragged nor ready to give up blooming, which is saying something in late August. It is found in the Botanic Garden's National Garden, along with a wild sea holly species that is just dazzling. Eryngium aquaticum holds aloft clusters of spherical flower heads that are silvery white with blue tints. Plant enough of them to have an effect: The stand at the National Garden forms a ribbon about 12 feet long and 8 feet across. It dances in the hot winds of high summer.

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