By Alice Marty/contributing writer
Q: Recently our garden club had quite a discussion about the hardiness of hibiscus in the Mobile area. I say they are not, but several members thought otherwise. Perhaps you could settle our disagreement.
A: Well, how about a hardy hibiscus? Yes, some hibiscuses are hardy in Alabama. Local gardeners have long loved the tropical hibiscus, hibiscus rosa-sinensis, seen commonly in the landscapes of south and central Florida. These evergreen shrubs with dark, glossy leaves and large, flamboyant flowers in shades of red, gold, orange, yellow, pink and white are popular in pots and in the ground. But, as almost every winter reaffirms, the tropical hibiscus is not reliably hardy when planted in the ground in zone 8b.
Unlike their tropical counterparts, hardy hibiscus, botanically known as hibiscus moscheutos, is more cold-hardy, vigorous and long lasting. They can grow quickly up to 8 feet tall and 4-6 feet wide. They are close relatives of the tropical hibiscus but have larger flowers. The blooms, measuring 6-12 inches across, are impressive, to say the least. Your neighbors’ heads will turn when they see these giant flowers. Strangers may stop and ask you to identify the huge blooms. William. C. Welch, professor of horticulture at Texas A&M University, calls these plants “giant rose mallow,” and explains that they “have the largest flowers of any cultivated perennial.”
These plants are native to marshy areas of North America. Being herbaceous perennials, they lose their leaves and the branches die back with the coming of winter, then resprout from the ground the following spring. They are root-hardy to zone 4 with some protection.
For years, the only hardy hibiscus colors available were white, pink and red, but over the last decade plant breeders have provided new colors and combinations. Mauve, hot pink and purple combinations with ruffled edges and overlapping petals can be found. Hardy hibiscus flowers, though tough, look delicate, resembling crinkly crepe paper. Each exotic bloom typically lasts only one day, but many open each day over a long blooming season until frost cuts them down. The blooms are also a magnet for hummingbirds and butterflies.
The new hybrid varieties sport foliage varying in color from bright green to burgundy and almost black. The “too large” size has also been addressed. Plant size has been scaled down to the 2-to-3-foot range, making them ideal for pots. “Indeterminate” is a term many have heard regarding tomatoes, and that trait has been bred into newer hibiscus varieties, meaning more blooms from top to bottom of each stem, not just at the tips.
A hibiscus needs a minimum of six hours of sun each day. It can be afternoon sun if supplemental water is supplied the first year. Remember, they were marsh plants at one time, yet a well-draining area works best. After being in the ground a couple of years, they can tolerate dry or moist conditions.
They are not particular about soil and will grow in most areas with a little water-soluble fertilizer added. Of course, improving the planting site with aged compost will insure better growth. Hibiscus work well planted as specimens or interplanted with perennials. Staking should not be needed except for the first year. If you want to encourage better branching just pinch them back lightly early in the growing season.
When plants begin to go dormant, cut old stems back to 3-6 inches above ground level. An important thing to keep in mind: Hardy hibiscus is very late to emerge in the spring. Be patient! They make up for their late start with rapid growth and should be blooming May through October.
The major insect pest of hardy hibiscus is the caterpillar-like larva of the hibiscus sawfly, atomacera decepta. Several of these larvae often feed on the same leaf or plant and can quickly defoliate the entire plant. The least toxic way to eliminate the sawfly larvae is by picking them off; find them on the underside of the leaves. Other pests include whiteflies, mealy bugs, grasshoppers and spider mites. The primary diseases are various leaf spots caused by cladosporium, cercospora, phyllosticta and other fungi.
Check with your local Alabama County Extension Office Master Gardener Home Garden Helpline, 877-252-4769, before using pesticide or fungicide. We can help you decide on the best course of action for the most satisfactory and safest results. Refer also to this publication: https://tinyurl.com/ya2d5nax
You are invited to these upcoming gardening events
What: Roses for the Gulf Coast
When: Wednesday, June 28, 10:30-11:30 a.m.
Where: Bellingrath Gardens & Home, 12401 Bellingrath Gardens Road, Theodore
Admission: Fees apply; call 251-973-2217 for more information.
What: Mobile Master Gardeners Monthly Meeting
When: Thursday, Aug. 3, 10:30-11:45 a.m.
Where: Jon Archer Center, 1070 Schillinger Road N., Mobile
Topic: Favorite Plants for Mobile Gardens, Mobile Master Gardeners
Master Gardener Helpline: 1-877-252-4769, or send your gardening questions to [email protected]