The diverse world of the Hibiscus

The word diversity can mean a lot of things in the world of plants, especially when we talk about diversity within a genus. Plants are grouped taxonomically based on their shared characteristics, so plants within the same genus by definition are similar in many regards. They may differ in mature size or flower color, but for the most part their parts look the same, and they generally like the same soil conditions and sun exposure.

Hibiscus, for example, is a genus where the shape of the flower is incredibly consistent throughout the most prominent species within the genus (though color and size may fluctuate) as it leaf shape (again, size and color fluctuate). However, I consider the genus to be fairly diverse because of the range of cold hardiness and growth habits within the genus.

Here at the Pitt County Arboretum, we have Hibiscus syriacus, also known as Rose of Sharon, which is a medium sized shrub; Hibiscus coccineus, also called Swamp Hibiscus or Texas Star, a cold hardy perennial that dies back to the ground each winter; Hibiscus sabdariffa, also called Rozelle, a borderline hardy herbaceous plant that is normally treated like an annual in our area; and Hibiscus rosa-sinensis, a tropical hibiscus, a cold sensitive flowering shrub that we grow in pots and bring indoors to overwinter.

Of these, it is the Rose of Sharon that has my attention at the moment, as there are two growing here at the Arboretum in full bloom, one white with red centers, and the other bright pink with a darker pink center. I also have two blooming in my yard at home – the same white and red flowering type along my driveway, and a double blooming purple-pink type in the backyard. Individual flowers of Rose of Sharon (and many other Hibiscus) may last for only a day, but new blooms appear continuously over several weeks, creating a prolonged but dynamic floral display. Single flowers are wide bell-shaped, five petaled blossoms, with a prominent fused stamen and pistil poking out through the center.

Top: Double-blooming Rose of Sharon shrub. These can grow up to 8-12 feet tall, with a spread of 6-10 feet. Left: Close-up of a single, 5-petaled white flower   with  a  vivid   red   center   and 

prominent fused stamen and pistil. Right: Single, five-petaled pink Rose of Sharon flower, also with a deep red center.

Rose of Sharon is a multi-trunked shrub that grows to a height of 8-12’ tall and a spread of about 6-10’. Shrubs can be pruned to grow as a single trunk tree, if desired, with some effort. It grows in sun to part shade, though it will flower best in full sun. It tolerates a wide range of soil types and pH levels, and thrives to some extent on neglect, making it an easy plant to grow. It will struggle in extremely wet or dry soils, but will do well in nearly anything in between.

Though not a native shrub, Rose of Sharon has long been a familiar part of gardens in the Southern and Eastern United States. It can be a bit weedy, and is considered by a few states (Kentucky and Virginia) to be invasive, though North Carolina does not classify it as such. Pollinators, including butterflies, hummingbirds, and a number of bee species, enjoy foraging on its blooms.

Matthew Stevens is the County Extension Director and Horticulture Agent for North Carolina Cooperative Extension’s Pitt County Center. If you have questions about this article or gardening in general, please contact the Pitt County Extension Master Gardener Infoline at 252-902-1705.