Once exotic and rare, tropical hibiscus are now practically as common as petunias on northern patios. Along with cannas, palms and elephant ears, they can give any backyard the aura of an idyllic South Sea island – at least for the summer.
Thank modern propagation techniques for making tropical hibiscus plentiful, cheap and available at any garden center or discount chain store. Grown as a rounded shrub or trained to resemble a small tree, these plants are garden show-offs with silken blossoms in the shimmering hues of a tropical sunset.
Hibiscus reach their peak in late summer and early fall, so this month’s display should be nothing short of spectacular. But about the time you gather your last tomatoes, you’ll have a decision to make: Will you discard your hibiscus plants and start over next year, or will you try wintering them over indoors so they might live to spend another summer under your care?
It may partly depend on whether you have a suitable spot, ideally a sunny, cool (60 to 65 degree) room where plants can be positioned away from direct heat. If you want to save your tropical beauties, here’s how to do it:
Bring plants indoors when night temperatures drop below 50 degrees. Stop fertilizing and water less frequently, but try to boost humidity by misting often, running a humidifier or standing pots on trays of dampened gravel.
To foil common pests in dry, heated interiors – chiefly spider mites and white flies -- give your plants an occasional shower. Cover the soil surface with plastic wrap or aluminum foil, stand pots in the tub and sprinkle them with tepid water for five or 10 minutes.
In late winter, replace the top two inches of soil with a fresh potting mix that includes some slow-release fertilizer. Don’t repot unless roots are protruding from drainage holes in the bottom of your container.
In late February or early March, new buds will start to swell. Prune now, before rapid growth begins, to remove weak branches and maintain a compact shape.
Once night temperatures are above 55 degrees, acclimate your hibiscus to outdoor conditions. Put the plant in a shady, protected spot and gradually increase sun exposure over a week or 10 days.
When new growth appears, feed periodically with an all-purpose fertilizer. Water faithfully, but allow the soil surface to dry between dousings. Don’t use saucers under pots since hibiscus require good drainage.
Hibiscus kept indoors won’t bloom through the winter; the goal is to keep the plant alive and healthy. Even during the summer, hibiscus flowers last only a day – on the plant or cut, in water or not.
One way around the indoor-outdoor shuffle is to opt for hardy relatives of the tropical hibiscus. These are hybrids of the native rose mallow, Hibiscus moscheutos, and are still relatively unfamiliar despite their virtues. Hardy in climates as harsh as Minnesota’s, the moscheutos hybrids bear huge, disk-shaped flowers, eight to 12 inches across, in a color range from white through pink to dark red.
The Fleming Brothers of Lincoln, Nebraska famously spent 50 years producing varieties like ‘Kopper King’ with copper-red foliage and white flowers, the purple ‘Plum Crazy,’ and ‘Old Yella,’ the first yellow cultivar. More popular still are newer, compact types including the ‘Disco Belle,’ ‘Luna’ and ‘Splash’ series, which grow just two to three feet tall.
These smaller forms are suitable for containers, although they must go into the ground by Labor Day to adequately prepare for winter. Once frost kills the upper growth, plants can be cut back. Leave stems eight to 10 inches tall so you will know where plants are and can avoid disturbing them before new shoots appear in late May or early June.
Hardy hibiscus are drought-resistant once established but are adaptable and can even grow in damp or soggy soils. Like the tropical kinds, they want full sun (at least six hours) and regular watering. Two or three doses of all-purpose fertilizer each season will keep them happy.
Flowering begins in mid to late summer and continues until frost – a boon in the late-season garden. They combine well with other hardy perennials like daylilies, ornamental grasses and Russian sage and are nearly as care-free. Because they emerge so late, these plants are good companions for small, early spring bulbs that bloom before the new hibiscus foliage appears.
One possible downside: hardy hibiscus flowers might serve as a whimsical hat, but are far too large to tuck Gauguin-style behind one ear. If you try this romantic look with your tropical blossoms, do as the Pacific islanders do – it’s the right ear if you’re available and looking, the left if you’re already spoken for.
Mail-order suppliers of tropical hibiscus include Hidden Valley Hibiscus and Logee’s Greenhouses. Hardy types are available from Nature Hills Nursery and the Sooner Plant Farm, which specializes in Fleming hybrids.