In the Garden: Hibiscus and Their Cousins

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By Charles Kidder

Hibiscus coccineus
Hibiscus coccineus

Where do marshmallows come from? From the candy factory, of course, but originally they were made from mucilage in the roots of a mallow plant that grows in marshes. Technology marches on, however, and the modern marshmallow confection contains no material from the marsh mallow plant. Mucilage in your food may sound less than appetizing, part of the reason that okra has a somewhat mixed reputation. Okra, mallows, cacao, cotton, and several other plant genera are all part of the large Mallow plant family, also known as the Malvaceae. If you’ve ever observed the flowers of either an okra or cotton plant, you may have noticed a resemblance to a familiar garden plant, the hibiscus.

Hibiscus is another one of those highly considerate plants with the same common and scientific names. Very convenient. The approximately 300 species hail from tropical and warm-temperate regions of the world, and in our area we can grow several herbaceous species and varieties, as well as one woody shrub.

The Rose of Sharon (H. syriacus) is our sole woody hibiscus and was formerly known as Althea syriacus, before some dedicated taxonomist decided it would be happier living as a hibiscus. Despite the “syriacus” epithet, it is not native to the Middle East, hailing instead from East Asia. Easy to grow, Rose of Sharon prefers full sun, but tolerates some shade; it accepts almost any moisture level except bone dry or soggy.

Depending on the variety, ROS can top out at 6’-12’ and be about 2/3 as wide.  The 2”-4” diameter flowers have the typical symmetrical hibiscus shape seen on Hawaiian shirts, a prominent central stamen, and range in color from white to pink, purple, bluish and various combinations of these.  Often the center of the flower has a darker-colored spot or blush.  The straight species has five-petal flowers, but there are double-flowered cultivars as well.

One issue with the Rose of Sharon: its tendency to seed around prolifically.  Much of the work done by plant breeders attempts to address this, so look for cultivars that are marked as either sterile or nearly so. Some of the early sterile varieties came from the U.S. National Arboretum and are sometimes known as the Greek Goddess series. ‘Diana’ has pure white flowers and waxy, dark green foliage; however, plant guru Michael Dirr reports that it is not a particularly vigorous grower and needs staking to keep it from splaying. ‘Minerva’ is more erect-growing and sports lavender flowers with traces of pink and a dark red central spot. It produces few, if any, viable seeds.

Rose of Sharon flowers for most of the summer, certainly a selling point. Unfortunately, when not in flower it’s essentially a somewhat raggedy green haystack, and when the leaves are off, an ungainly bunch of sticks. Sorry, we pull no punches here. Up in Zone 5 it’s a reasonable contender for garden space, but in the south it has to compete with crape myrtles for attention. (I’ve always thought that an allee or hedge alternating ROS with crape myrtle might be attractive.) But if you combine Rose of Sharon in a bed with other shrubs and perennials, it can be a nice addition to your property.  Just don’t plunk it in the middle of your lawn as a specimen.

If you don’t want to commit to the large size and underwhelming off-season presence of Rose of Sharon, consider the many perennial hibiscus. One of the more commonly grown species, Rose mallow (H. moscheutos) grows to about 3’-4’, with five-inch flowers in colors ranging from white to rose, pink and purple. There are several cultivars of this plant, many of which are probably some type of complex hybrid. ‘Cherry Cheesecake’ has creamy white petals, a central raspberry blotch, and pink veins. ‘Kopper King’ stands out for its coppery-red-purple leaves that showcase the white flowers. All of the rose mallows prefer abundant moisture, but tolerate average conditions. And again, in the spirit of total disclosure, the rose mallow does have some issues, particularly Japanese Beetles. They can reduce the foliage to lacy skeletons, so pick off the little rascals and squash them. Avoid sprays and other nastiness that will kill every other insect that happens by.

If you want to avoid the Japanese Beetle scourge, try planting scarlet rose mallow, H. coccineus. For some unknown reason, the beetles don’t chomp on this species.  (Hope I haven’t jinxed things here…) Native to the coastal plain of the southeast United States, this perennial can reach heights of seven feet once it gets established.  The foliage is sparse and cannabis-like, topped by 5” screaming-red flowers. If you prefer something more subtle, the cultivar ‘Swamp Angel’ has white flowers. Like the rose mallow, this species likes water but is okay with moderate moisture.

What if you want a hibiscus with yellow flowers? Your choice would be the sunset mallow, a.k.a. sunset hibiscus. It’s not really a hibiscus, following the scientific name change to Abelmoschus manihot, so “A rose by any other name…” A perennial or reseeding annual that reaches five feet in height, it’s actually in the same genus as okra. The leaves are reportedly tasty and highly nutritious.

And speaking of the edible parts of hibiscus, the tea that you might have encountered on store shelves comes from Hibiscus sabdariffa, a tropical plant grown widely in warmer climates. Even if you could grow it here, I doubt there would be time for the calyces to mature and be used for the tea.

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