Perennial hibiscus (Hibiscus moscheutos) left, Chinese hibiscus (Hibiscus rosa-sinensis) middle, rose of sharon (Hibiscus syriacus) right. Photo: http://www.plant-world-seeds, http://www.amazon.ca & http://www.villagenurseries.com
I receive a lot of gardening questions and a surprising number concern hibiscus. Either a lot of people are growing hibiscuses or a lot of people are having trouble with them!
The problem is, I can’t answer a question about a hibiscus plant without knowing which hibiscus you’re referring to. So, it would help me (and you) to know which hibiscus you are growing.
Yet, to many gardeners, a hibiscus is a hibiscus, period. How complicated can it be?
Very complicated, actually.
Three Out of Hundreds
There are actually hundreds of species of Hibiscus found all over the world, including annuals, perennials, shrubs and—yes!—even trees! Some are grown as ornamentals, others for their edible flowers and fruits and even some for their fibres! All, of course, are in the mallow family (Malvaceae) and their flowers look a lot like mallow blooms, but bigger.
However, when most people refer to hibiscuses, they have one of three species in mind, all, initially, with similar flowers: large and disc-shaped with 5 broad petals and a striking central column composed of anthers surrounding an even longer style. All come in various colors and can be simple, semi-double or double and most have flowers that last but a day, sometimes two, but, of course, all bloom repeatedly.
Let’s look at all three.
Perennial Hibiscus, Hardy Hibiscus, Rose Mallow or Swamp Rose Mallow (H. moscheutos)
This hibiscus is a herbaceous perennial and is hardy from USDA hardiness zones 5 to 9, even zone 4 with a little winter protection. It can be very tall (up to 15 feet/4.5 m!), but modern cultivars are usually in the 3 to 7-foot range (1 to 2 m). Its stems are quite woody for a perennial and need to be cut back in spring.
Perennial hibiscus starts its growth cycle very late in the spring, often a full month after other perennials have started to sprout, but then grows quickly. It produces huge flower buds that open into giant flowers, often said to be dinner-plate size and that’s scarcely an exaggeration: some are 9 inches (25 cm) in diameter, by far the largest flower of any perennial. They come in a wide range of shades, from white to pink, red and purple, often with a red eye.
It can be a very late and brief bloomer colder climates, but has long blooming period, from July to September, in milder ones.
Its leaves are quite variable and can be broadly ovate to lanceolate, even heart-shaped, and sometimes bear 3 to 5 shallow lobes. Curiously, the shape can vary on the same plant. They are usually medium green (some cultivars have bronze foliage).
It’s the only one of the three commonly grown from seed.
Rose of Sharon, Shrub Althea and Shrubby Hibiscus (H. syriacus)
This hibiscus is a shrub adapted to temperate climates: USDA hardiness zones 5 to 8, even 4 with winter protection. It reaches 7–13 feet (2–4 m) in height and branches abundantly.
It has the smallest flowers of the three, but still, they are about 1½ to 4 inches (4 to 10 cm) in diameter and very showy. They come in white, pink, red and “blue” (blue-violet), often with a red or purple eye. It also has the smallest leaves of the three, with three distinct lobes.
Chinese Hibiscus, Tropical Hibiscus or China Rose (H. rosa-sinensis)
Of unknown origin, this plant is a tropical shrub and is only grown outdoors year-round in tropical or subtropical climates (USDA hardiness zones 9 to 11). That said, it is also widely available in temperate climates as a houseplant and patio plant.
Chinese hibiscus can be anything from 1 to 12 feet in height (30 cm to 4 m) and has woody branches. The flowers, usually about 3 to 8 inches (7.5 to 20 cm) in diameter, come in a wide range of colors: red, pink, white, yellow, peach, orange or purple.
It can flower all year long, although generally mostly heavily in spring and summer when grown as a container plant or houseplant. Leaves are dark green (sometimes variegated) and ovate with toothed edges.
Obviously, since it’s a tropical plant, it tolerates no frost.
So, three hibiscuses, all with far too many common names: one a perennial (H. moscheutos), one a temperate shrub (H. syriacus) and one a tropical shrub used as a houseplant or patio plant (H. rosa-sinensis). Give all of them full sun, never let them dry out completely, fertilize occasionally and apply whatever special conditions they need to get them through the winter. But you do need to know which is which if you’re going to succeed with them … or if you want to ask questions about them.