Green Thumb – Beautiful Hibiscus

Posted: August 14, 2019

I need a bumper sticker with this phrase: “I brake for hibiscus.” I saw a plant last summer with flowers so big they looked like pink dinner plates hanging on a bush. Who could drive by without stopping to look?

If you’ve never seen flowers this big, you might think it’s a tall-tale, but some hibiscus can produce eye-popping flowers 12 inches across. Regardless of their flower size, all hibiscus varieties have beautiful though fleeting flowers that usually last a day. They make up for it with constant blooming that attracts butterflies and hummingbirds.

There are three types of hibiscus you can grow.

The Tropical Form

The tropicals are the flowers you see on Hawaiian shirts, sometimes called “exotic” or “fancy.” They have a long bloom season and shed just a few leaves at a time. In our area they should be grown in pots and brought indoors when temperatures drop below 50. A freeze below 25 degrees will kill them.

The flowers are typically 4-6 inches across in shades of yellow, orange, red, pink, or multicolor, and can be as large as 8-12 inches. Many have an eye of contrasting color and some have ruffled petals. The leaves are a beautiful glossy green.

For the best flowering they prefer about six hours of sun, but will grow in partial shade. Give them lots of water in warm weather, but less when the weather cools.

When you bring them indoors prune them back as much as a third and spray them with an insecticidal soap because they are prone to whiteflies. Place them in a window with as much sun as possible. They will drop leaves, but will develop new growth as they adjust to the move. Take care near the flowers because they have prominent pollen structures that can stain.

The Perennial Form

The perennial hibiscus, known as “Rose Mallow,” has large flowers and leaves. There are two types. The “determinate” varieties grow to full height and then have flowers at the tips of the stems. The “indeterminate” have flowers up and down the stems, producing more flowers for a longer time.

Perennial hibiscus stems die to the ground each year and are one of the last plants to wake up in the spring. Before new growth appears at the base of the plants, prune out the dead woody stems. Mulch them the first winter, but remove the mulch before new growth starts.

These plants like lots of water, full sun and hot, humid weather for the best colors and most flowers. Don’t let them wilt or they might drop their flower buds. Once they start to grow, apply a balanced slow release plant food to the surrounding soil. Then give them water soluble plant food in early summer just as flower buds begin to form.

Once they start growing in the spring, they will gain about an inch a day. Blooming starts in mid-summer. The flowers are white, rose, pink or red, often with a dark center. This plant can reach six feet tall and wide. The dwarf varieties grow three feet tall.

The Shrub Form

The shrub form of hardy hibiscus is called “Rose of Sharon.” They have woody stems. The abundant 3-4 inch flowers can be single or double in shades of pink, purple, or white with contrasting eye. They bloom along the stems from midsummer to fall.

Plant them in average, well-drained soil and in full sun, for best flowering. Most varieties can reach 12 feet and spread 6 to 10 feet. To keep them smaller, prune them in spring. The dwarf series grow 3-4 feet tall. Rose of Sharon typically grows in a multi-stemmed vase shape. They look good as a screen, or as a feature. Keep them well-watered going into winter.

If you do select one of the varieties with flowers the size of a dinner plate, think twice about growing it in your front yard. Its beauty might cause a traffic jam.

 

Janice M. Weber – University of Illinois Extension, DeKalb County Master Gardener

 

GOT A GARDENING QUESTION?

Submit your questions to connections@dekalbfarmbureau.org. or call the University of Illinois Extension Horticulture Help Desk at 815-758-8194. The Desk is open for questions now to mid-October from 9 a.m. – Noon.


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