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Ask Dayle

9/5/2013 - West Side Leader
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By Dayle Davis

Pictured is hardy hibiscus that produces dinner-plate-sized blossoms and can safely winter over outdoors.
Photo: Dayle Davis
Q: I have a hibiscus tree whose leaves are turning yellow. It was healthy when it was inside, and I’ve had it for about three years. I didn’t place it outside this year until the weather got warmer, about the second week of June. Since then, the leaves are turning yellow and it hasn’t bloomed once. There are a lot of buds on it now, however. I keep it watered and it is in a mostly sunny spot in my yard. Can you tell me what’s wrong with it?

A: There are hardy hibiscus, which will winter over safely planted in the garden, and tropical hibiscus, which must be treated as a houseplant. Since you keep your hibiscus indoors until warm weather, I assume your plant is a potted tropical hibiscus. Tropical hibiscus are wonderful plants that provide summer-long blossoms for the backyard deck or patio. Being tropical means that the plant will not withstand frost or winter weather in Northeast Ohio.

It’s not unusual for hibiscus leaves to turn yellow and drop from the plant. This happens for any number of reasons and is a sign of stress.

For example, if you’ve watered your plant too little or too much, it will drop its leaves. Strive for soil that is moist and well draining but not soggy.

Perhaps the climate is not to the plant’s liking. On severely hot or windy days, the plant might need more water than you gave it; if the weather is chilly and cold, the plant may yellow and drop some leaves.

Hibiscus that are kept indoors normally react with yellowing leaves if they are suddenly thrust into full sunlight conditions. Too little light also will cause leaf drop. Try to moderate the amount of light your plant receives each day.

An infestation of spider mites could be the culprit, as well. These tiny spiders suck the juices from the underside of leaves, which will first manifest as a mottling of the leaves, which begin to look sooty and unhealthy. As the mite infestation takes hold, there will be small spider webs under the leaves and at the ends of stems. Finally, leaves will yellow and fall off the plant — sometimes the entire plant will be denuded. Stay vigilant about your insect patrol.

To safely bring your plant back indoors for the winter, it will have to be acclimated first, before bringing indoors. In other words, tropicals and houseplants that are not winter hardy need a period of transition before over-wintering inside in a heated environment. To begin, do not fertilize after mid-August. In early September, move your potted hibiscus into the shade to help to keep the soil and root ball cool and moist. In about 10-12 days, cut back the hibiscus by approximately two-thirds and repot the plant. Keep the newly potted plant in its shady spot outdoors for another 10 days before bringing inside. If there is any chance at all of a frost, bring the plant onto a covered porch or into a garage or other unheated covered space for protection. A hard frost will completely kill the plant.

Once inside, place the pot where it will receive bright indirect light, not sun and not so close to a window that the plant can feel cold through the glass. Water just enough to keep the soil barely moist through the winter. Begin fertilizer in early spring and increase watering just a bit, but do not waterlog the soil. Fertilize at about half the recommended strength. Use an all purpose fertilizer such as 10-10-10, although some gardeners prefer the results they receive from a fertilizer ratio of 7-2-7.

In spring, reverse the acclimation process to safely return your plant to the outdoors.

After all chance of frost is past, place the hibiscus outdoors in the shade for a few days. After that, place the container in the sunlight for a short while, increasing the amount of time each day until the plant has reached the full amount of time it normally spends in the summer sun.

Once it is re-acclimated to the outdoors, check to see if your hibiscus needs to be repotted. Do not repot at the same time it is being re-acclimated. The plant may go into shock and not recover.

Prune to shape the plant and manage its size to invigorate an older plant and to remove diseased or dead wood. For best results, do not prune in spring until all chance of frost is past. If your plant is somehow damaged by frost, wait until you see new active growth and prune back to that level where there is viable undamaged wood. But again, wait until all danger of frost is past to accomplish this pruning.

To prune correctly, make a sharp clean cut on a downward angle just above the tiny node or bump-like protrusion that you can detect growing at the junction of leaf and stem. This node activates and begins to grow after pruning. Pruning invigorates the hibiscus and encourages budding.

For more information, call The Ohio State University Summit County Extension Hotline Tuesdays from 9 a.m. to noon at 330-928-4769, ext. 3, and Request Fact Sheet HYG-3068-96, “Diagnosing Problems on Indoor Plants.”

Please note fact sheets are sent out free; there is a fee for bulletins. Many bulletins are available online at ohioline.osu.edu and can be printed from home or accessed at the public library.

Dayle Davis is a freelance writer and avid perennial gardener, with a B.A. in communications and course work in botany, geology and wildflowers. Davis is a master gardener emeritus under The Ohio State University’s Horticultural Extension. Readers can send in questions regarding lawn and garden issues, which could be featured in a future edition, as well as about the OSU Master Gardener program. Questions can be emailed to kcollins@akron.com, faxed to 330-665-9590 or sent to Leader Publications, 3075 Smith Road, Suite 204, Akron, OH 44333. Please do not send any leaves, seeds or other organic material. Inquiries about area garden clubs or groups should be sent directly to the particular organization in question.

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