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Gardening: Hardy Hibiscus

As the vivid colors of early summer fade, native hardy hibiscus makes an appearance in dramatic style.
Martha Stewart Living, July 2011

Hibiscus seems exotic. We think of India or Mexico, of sarong-clad Hawaiians with a single blossom tucked behind the appropriate ear. Yet some of the most spectacular hibiscus are native to temperate North America, where they bloom happily and easily in summer gardens as far north as Zone 4. They appear late in the season, after midsummer. Each bud lasts only a day, but there are many, which means that hibiscus can flower for weeks when few other perennials are in bloom.

Hibiscus moscheutos (swamp rose mallow) grows wild near ponds, salt marshes, and upland wetlands from Massachusetts to Wisconsin, Florida to Texas. You may come upon the huge, simple flowers -- clear pink or white -- swaying on six-foot stems among reeds or grasses. Wherever they grow becomes a wonderland.

These wild hibiscus and their cultivated cousins are surprisingly adaptable to gardens. Given a wet locale, they will be grateful. But even without one, they will bloom with regular watering and some compost. They love full sun but can manage in partial shade, especially if that shade comes in the afternoon.

Most hardy hibiscus hybrids found in garden centers stay close in form and color to their splendid native progenitors. They grow from four to eight feet tall; their flowers open six to 12 inches across. The plants look most harmonious when arranged in ways that echo their natural habitats: grouped in clumps of two or three, and allowed to tower in the back of a border amid tall grasses or billowy shrubs.

The tallest stems will sometimes topple, especially in shade. Keep them upright with a couple of stout bamboo sticks and twine wrapped around them as the stalks develop. Some varieties have been selected for shorter stems -- four to five feet, which can save staking and be helpful in smaller spaces. 'Lady Baltimore' is one of these, with flowers in a lovely pink. Others include the red 'Lord Baltimore' and 'Blue River II,' which blooms an unexpected brilliant white. Just watch out for the plant breeders' extremes: Twelve-inch flowers on two-foot stems, for instance, can have trouble supporting their own weight.

Hibiscus usually dies right down to the ground over winter. First shoots return in late spring, so mark them well, or leave part of their woody stems uncut so that you know where to expect them. Gardeners in colder places can enjoy hibiscus as annuals if they plant them from pots. Those at the other end of the range, in Zones 6 to 11, can grow the vivid native scarlet swamp mallow, Hibiscus coccineus.

Bees and other pollinators love hibiscus. But so do Japanese beetles. Look for their shiny backs, and pick them off in the early mornings if holes appear in leaves or buds.

Your efforts will be rewarded when, suddenly, those big buds open wide. Fresh petals of pink, white, or red will flutter against the deep blue of August and September skies, and summer will be reborn.

Great Late Bloomers

Hibiscus thrive in temperate gardens and wild marshes, some soaring above seven feet, others standing at more modest heights.

1-3. Hibiscus moscheutos is the native swamp rose mallow; its pink, white, and red flowers grow on four- to seven-foot stems.

4. The large warm-pink flowers of 'Lady Baltimore' have red eyes and usually appear on easy-to-manage four-foot stems.

5. 'Blue River II' has pure-white, crinkly flowers and blue-green leaves.

6. A compact plant, 'Fantasia' produces lavender flowers that have deeper eyes.

7. 'Sweet Caroline' has rose-pink, ruffled petals and grows four to five feet tall.

8. H. coccineus is a Southern native that will grow in Zones 6 to 11; it can reach heights of 10 feet with delicate-looking blooms.

9. 'Fireball' produces some of the biggest and boldest flowers in the garden -- 12 inches across and deep red -- on five-foot stems.

In Living Color

Each brilliant bud lasts only a day, but there are so many that hibiscus can flower for weeks.The flowers look their best growing in loose clumps, as they do in nature. Special thanks to the New York Botanical Garden (nybg.org). Hardy hibiscus are available at Wayside Gardens (waysidegardens.com) and Plant Delights nursery at Juniper Level Botanic Gardens (plantdelights.com).