Few perennials are as flamboyant as hibiscus. Their flowers can be up to 10 inches wide or larger, which is inconceivable for something that’s not tropical. Hibiscuses have been in gardens for a long time, but with all the recent enhancements in flower colors and sizes, foliage shapes and hues, and compact habits, they’re not the same as grandma’s plants anymore. Although I think they’re fun and the perfect antidote to fussy landscapes, my impression is that people either love them or hate them. The gigantic flowers are exotic and charismatic to some, while others find them too big and garish.

Their size isn’t the only thing that’s not subtle. They put their sex right in your face: The male and female reproductive parts are held on long bottle brushes that protrude from the centers of the flowers with a bright red bull’s-eye marking the base of the column. Many older selections are more plant than flower, but newer cultivars have been bred to be indeterminate. The result is more flowers from tip to toe and a longer bloom period, which is the case with the following favorites from our trial.

Hibiscus At a Glance

Hibiscus spp. and cvs.

USDA Hardiness Zones: 5 to 9

Conditions: Full sun to partial shade; moist, well-drained soil

Bloom time: Mid- to late summer through early to midfall

Propagation: From cuttings off new growth, from seeds, or by division in spring

Maintenance: A late-spring pinching can force plants to have a bushier habit

When ‘Cranberry Crush’ bloomed for the first time, I was immediately captivated by the boldness of its deep scarlet-red flowers—the color is so intense that the red eye is barely discernible at the center of the slightly cupped petals. Equally fun are the nearly black flower buds that swell like balloons before opening. The maplelike leaves start a shiny deep bronze but turn dark green with purple overtones later in the season. ‘Cranberry Crush’ received high marks for its great flower show, dense rounded habit, and reliability, but to be honest, the vivid flowers could be plunked on a stick and I’d still be crazy about this plant.

Objectivity is key to a fair trial, but it’s too easy to have favorites. Right now, it’s ‘Heartthrob’. The deep blood-red flowers with darker black-red eyes are irrepressibly seductive, while the whopping 9-inch flowers only heighten the allure. The oval-shaped leaves and stems are green at all times—it’s like there was no more color to spare! ‘Heartthrob’ makes a neat, compact bush about as tall as wide, which you’ll appreciate all summer but probably won’t give much thought to once the flowers pop.

Hibiscus Trial Results

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Caring for hibiscus

Keeping these plants healthy and happy doesn’t take much effort. Rusts, leaf spots, and stem and crown rots can be problems. Here are a few other things to note about their nature.

 

Flowers

The blooms—either flat or slightly cupped—have broad overlapping petals that may be puckered or ruffled, making them look a bit like crepe paper. The delicate petals are deeply etched with veins, which are sometimes a different color, and the red spot at the center varies in intensity. The flowers are fleeting. Each blooms for only one day, but flowers open in succession over many weeks.

 

Habit

Hibiscuses are bushy plants with shrub like proportions, ranging from a few feet to more than 7 feet tall. Whether taller than wide or as wide as tall, stems are typically strong enough to stay upright no matter the height.

 

Foliage

The classic leaf is broadly oval with a few shallow lobes, but many cultivars feature maplelike leaves (photo above), which are strongly lobed to deeply dissected. Leaves can be simply green or blushed with shades of purple, burgundy, or bronze. While these accents may fade quickly, some of the newest cultivars stay deep burgundy or purple all summer long. Leaf margins, veins, and petioles as well as stems often show some red to burgundy, too.

 

Pruning

Stems can be cut back in fall or spring; it’s best to leave some stubs to mark their location because hibiscuses emerge pretty late in the spring.

 

Deadheading

Since each flower lasts for just a day and is so large, deadheading might be crucial for neat freaks. In dry weather, the large flowers fall cleanly from the sometimes chartreuse calyxes. But if the flowers are wet when they drop, they turn mushy and stick to the leaves in an absolutely detestable way. I’ve certainly peeled my share of soggy flower carcasses off the leaves to improve the display.

 

Flea beetles

These tiny, shiny black insects can be easily overlooked until you notice little shot holes on the leaves. The damage is a minor cosmetic issue at best, but in severe cases, hungry flea beetles can turn a leaf into a sieve. Interestingly, the shot holes are less noticeable on purple or burgundy foliage than on green-leaved plants. Diatomaceous earth is a nontoxic way to help kill them off.

 

Japanese beetles

Japanese beetle damage was less prevalent on our hibiscuses, likely because local beetle populations have gone down in recent years. The damage can be considerable due to their voracious appetites, leaving behind skeletonized leaves and flowers. Handpicking is an effective, albeit gross, control option.

 

Sawfly

Hibiscus sawfly larvae can be an issue, too, and generally first appear on the underside of the leaf and begin feeding. In a couple of days, these caterpillar-looking creatures will turn the leaves of the hibiscus into skeletonized lace. Organic horticultural oils can help kill off some of the offenders.

 

Richard Hawke is plant trials manager at the Chicago Botanic Garden.

Photos, except where noted: Danielle Sherry; Carol Collins.

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Sources

Davidson Greenhouse & Nursery, Crawfordsville, IN; 877-723-6834; davidsongreenhouse.com

Garden Crossings, Zeeland, MI; 616-875-6355; gardencrossings.com

Plant Delights Nursery, Raleigh, NC; 919-772-4794; plantdelights.com