In the world of garden shrubs, the rose of Sharon has a lot going against it. The leaves are drab with no fall color; the bush is twiggy, stiff and ungainly; and the light-gray bark is simply dull. But the rose of Sharon has one redeeming quality: In mid- to late summer, it has something few other garden shrubs can produce: blossoms.
We speak not of the demure, pearly blooms of the mock orange or spirea, but brassy saucers surrounding a central spike of pollen. Think of it as a satellite TV dish for the fairies.
It is this flower ornament in the dog days of summer that elevates the plant. Among trees and shrubs, there isn’t much else in flower in August — a month when certain perennials and, especially, ornamental grasses come to the fore. If you discount roses, the gardener is scrounging for action from trees and shrubs and turns to crape myrtles, the Japanese pagoda tree or the PeeGee hydrangea.
Overshadowed by an ever-expanding palette of crape myrtles, the tired old rose of Sharon seemed to have vanished from view, or at least the gardener’s consciousness, but, lo, its star is ascendant once more.
For reasons more to do with serendipity than a grand plan, the rose of Sharon is in the midst of its most comprehensive makeover in years, maybe ever. The resulting varieties are coming closer to creating a shrub that can be integrated into the garden as worthy ornamentals and not just because they plug a flowering hole.
Breeders in Europe and South Korea are developing versions with better flower colors and forms, and plant shapes that are smaller and generally less awkward.
“They aren’t always the most easy plants to use in the landscape; to have a more rounded, denser habit is something we look for,” said Stacey Hirvela, of Spring Meadow Nursery in Grand Haven, Mich. The wholesale company develops and distributes shrub varieties under the Proven Winners brand.
Rose of Sharon blooms are redolent of the tropical hibiscus plants found growing in patio and balcony pots, and to the plate-size blooms of the native rose mallow. All belong to the genus Hibiscus. Botanically, the rose of Sharon is Hibiscus syriacus.
Another one of its faults is its prodigious seeding: You will find old specimens — they are hardy and live as long as lilacs — with dozens of seedlings growing at their feet. The fastidious gardener would remove the blooms as they faded to prevent seed set. This chore, if it was ever popular in Washington in the heat of August, is no longer a favorite pastime.
Several years ago, a series of new varieties from the U.S. National Arboretum revived the shrub’s fortunes. The first, named Diana and producing white flowers, was released in 1970 and was followed in the 1980s by Aphrodite (pink with red eye spot), Helene (white with red eye spot) and Minerva (lavender with red eye spot). The flowers were large and durable, and because they were sterile, or nearly so, the shrubs just kept blooming for weeks. (Plants typically stop growing new flowers when fertilized.) This sterility also solved the problem of the self-sowing of seeds. Aphrodite, the largest of the group at nine feet high, has become the most widely used, in my experience.
Blue is a choice color in this plant, and the standard variety for this was Blue Bird. I always thought this a valuable plant in the back of a border, where its ugly ankles and twiggy habit could be disguised until it took the stage in midsummer. But I haven’t grown it, and I read that it has problems beyond seeding: It’s open in habit and has a short season of bloom. It has been superseded by Blue Satin, a stronger color and a better grower. I recently saw a 10-year-old specimen that had reached 15 feet.
Blue Satin sets seed, however, and has been upstaged by a seedless version named Azurri Blue Satin. It is one of several Satin varieties developed in the United States by Spring Meadow as a line of large, single and sterile or near-sterile shrubs. The group also features Blush Satin, white blush; Rose Satin, pink; Ruffled Satin, pink with a burgundy eye; Orchid Pink; lavender-pink with a prominent red eye; and Violet Satin, violet with a red eye.
One of today’s most interesting breeding programs can be found on a six-acre farm in the east of England where a retired Cambridge University professor named Roderick Woods has been working his magic. In his academic incarnation, Woods was an expert on human physiology and developed protective clothing for hazardous occupations, but his fascination with the rose of Sharon has abided since his childhood in the 1950s, when his parents grew them.
As a breeder, he has been working on improving the size and color of the flowers — they are traditionally muddy and age to a gray — and he has raised 18,000 seedlings to flowering age since 1980. The vast majority are discarded in the quest for a better rose of Sharon. While trying to develop a stronger single pink from seed sent from Japan, he found seedlings that were slightly double — they’re known as anemone-flowered — and from this came the Chiffon line, now gaining traction in U.S. gardens. The series features Pink Chiffon, White Chiffon, Lavender Chiffon and Blue Chiffon. The last was the hardest to develop because of the recessive nature of blue-flowered genes, but the wait looks worth it, with large blue flowers at eye level in late summer.
Woods seems even more excited about a line of new single-flowered types in pink, white, deep purple, dark red-purple and light red. “The flowers are 50 percent bigger than others and open perfectly flat with overlapping petals, so the flower power is better than anything else on the market,” he said. They are being trialed in Europe, but their appearance here may be harder to achieve because of new restrictions on hibiscus importation to safeguard citrus growers against a pest risk.
One other drawback to rose of Sharon is the sheer size of the shrub. This is not a plant for a small urban garden. However, in Korea, a breeder named Kyung-Ku Shim has developed dwarf varieties named Lil’ Kim. Three are available in the United States, in red, violet and white. Beyond their size — at three to four feet, they are less than half the size of a regular shrub — the dwarf varieties have a more pleasing leaf texture and overall habit.
“These varieties have very small leaves and really dense bud set, so instead of looking at a mass of foliage all season, they have a more elegant habit,” Hirvela said. They are also sold under Proven Winners’ ColorChoice brand and have wide distribution in independent garden centers known for their range of woody plants.
Another innovation is a variety named Purple Pillar, developed in the Netherlands. It has semi-double flowers, pink-purple with extended red eyes, and although it grows as tall as a regular rose of Sharon, it gets just three feet wide. Because I have a young plant, I haven’t seen it in its glory, but I think this would be a good vertical accent in a border of seasonal highlights.
Another developer and grower of new varieties, Bailey Nurseries in Newport, Minn., has introduced four semi-double flowered varieties — Tahiti, Fiji, Hawaii and Bali — with a size and intensity that suggest tropical blooms. This year it introduced the first in a series of French-bred plants that are fully double in bloom, as frilly as a carnation. The first is French Cabaret Blush, which is soft pink and white.
The rose of Sharon likes heat and sun, another reason it’s so valuable in summer, and will take dry conditions once established but will benefit from some moisture. It’s also deer-resistant. Woods recommends cutting the shrubs back hard every six years or so, to reinvigorate the flowering.
Debbie Lonnee, of Bailey, sums up the appeal of this shrub and why it’s time to embrace it again: “It’s a super summer-blooming plant with a lot of appeal,” she said. And it stays that way until September, bridging that awkward dead time in the garden known in horticultural terminology as August.