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Growing Together: Make hibiscus feel at home

I've got a riddle for you. Why is rhubarb pie like a tropical hibiscus plant? While you're pondering the answer, let's describe hibiscus. Most garden centers sell hybrid hibiscus having large showy blossoms of pink, rose, orange or yellow growing...

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Hibiscus' native habitat provides clues to their preferred care. David Samson / The Forum

I've got a riddle for you. Why is rhubarb pie like a tropical hibiscus plant? While you're pondering the answer, let's describe hibiscus. Most garden centers sell hybrid hibiscus having large showy blossoms of pink, rose, orange or yellow growing as small single-trunk trees or multi-branched bushy plants. Although hibiscus belongs to a large family including cotton and okra, the object of today's attention is the large-flowered hybrid known as tropical hibiscus.

Give up on the riddle? Rhubarb and tropical hibiscus are alike because they both grow best if their native environments are duplicated by home gardeners. We can learn the secrets to their preferred care by examining their native homes.

Rhubarb, native to the cold-winter regions of Tibet and Mongolia, was taken west to Europe and eventually to America, where it established well most places, except for southern states. Rhubarb requires cold winters like its native homeland.

Likewise, we can learn about hibiscus care from their native home in the tropics of Asia and Africa where there's no frost, year-round temperatures are warm and mild, and seasons are distinguished as rainy and less rainy, rather than warm and cold.

They won't survive winters outdoors in hardiness zones colder than 9 or 10. Even Louisiana is iffy. But we can make hibiscus think they live in the tropics by bringing them indoors for the winter.

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Care after purchase. Most hibiscus are sold in spring as potted plants ready for decks and patios. Although hibiscus like full sun, new plants should be gradually acclimated in filtered shade for 10 days to avoid burning leaves. If you're planning to bring them indoors for winter, hibiscus should be left in their pots instead of planting in flower beds or landscapes.

Watering. In their native tropics, hibiscus receive a plentiful, even supply of rain during the season of active growth. Home gardeners can duplicate this by careful attention to watering, usually once per day. Apply enough so excess runs out the bottom drainage holes. Hibiscus shouldn't be allowed to dry out extensively or their overall health and flowering will suffer. Dryness in the tropics signals the end of the season of active growth.

Fertilizing. Tropical soils are rich and fertile, allowing hibiscus to feed heavily. Accommodate their appetite by fertilizing every two weeks during spring and summer. All-purpose Miracle Gro works fine. Hibiscus don't like the high phosphorous content of "blossom booster" fertilizers often recommended for other flowering plants.

What to do at summer's end. Tropical hibiscus are easily killed by frost. But hibiscus will think they're in the tropics if we bring them indoors for the winter, and then back outdoors next spring. Bring indoors before night temperatures fall consistently below 50 degrees to avoid chill injury.

First wash the foliage and stems with a generous spray from the water hose. This helps prevent aphids and spider mites from tagging along. Because these insects commonly cause problems for hibiscus indoors, it's wise to spray with insecticidal soap or neem oil after the foliage has been washed and dried. Spraying is easier outdoors.

Wintering hibiscus indoors. If the plant has become quite large over summer, prune to reduce size. Locate hibiscus in the sunniest indoor location possible, by patio doors, large windows or in a sunroom.

Short days and decreasing light levels will signal the plant to slow down. To encourage this natural rhythm, decrease watering frequency. This imitates the onset of the dry season in the tropics. Daily watering should gradually be replaced with weekly intervals. Fertilizing can be reduced to monthly feeding at half dose. Repotting should wait until late winter. Increasing pot size when the hibiscus is less active can make the plant flounder in too much soil, risking overwatering and root rot.

Leaves often turn yellow and drop. This is normal and they'll regrow when necessary. In the meantime, water sparingly. Don't push the plant to bloom indoors if it doesn't want to. It might need a rest. If it's growing and blooming, water accordingly.

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In late winter or early spring (February or March), lengthening days will signal the hibiscus to resume growth. This is the time to repot. Hibiscus enjoy being "potbound," and pot sizes between 10 and 14 inches in diameter are sufficient. Increase pot size only gradually, and scrape away a little of the old soil from the top and sides of rootball when repotting. Imitate the soil of the tropics by choosing a top quality potting mix high in peat moss. Prune away spindly winter growth to encourage fresh branching.

When night temperatures remain consistently above 50 degrees, hibiscus can be moved outdoors to a filtered sun location before exposing to full sun. And the cycle begins once more.

For owners of the increasingly popular tropical mandevilla and dipladenia plants, they can be overwintered just like hibiscus.

Don Kinzler, a lifelong gardener, worked as an NDSU Extension horticulturist and owned Kinzler's Greenhouse in Fargo. Tune in to his weekly radio segment from 11 to 11:30 a.m. Fridays on WDAY Radio 970. Readers can reach him at forumgrowingtogether@hotmail.com .

Related Topics: DON KINZLERGARDENING
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