Southern 'Swamp Thing' Goes National
Master gardener Maureen Gilmer shares her expertise on the elegant cold-hardy bloomer, Luna.
Rose Mallow casts her pearls before swine. When given a choice, she'd rather dwell in the mud of a mosquito-infested swamp than anywhere else. She is a native of the South, with its marshes and bayous, the ornamental cousin of cotton and okra.
The species, Hibiscus moscheutos, has long been a part of southern gardens. Some call her "dinner plate" due to the sheer size of her blossoms. A tolerance of saturated soils has made her invaluable to low-lying gardens or those with very poor drainage.
This is a marginal plant, found in the wild at the edges of ponds, swamps and rivers where the water levels fluctuate. This understanding is key to courting rose mallow's seemingly fickle behavior; she will tolerate both wet and dry conditions, but if too dry she may not appear as lush or vigorous.
These perennials are often confused with the Confederate rose, Hibiscus mutabilis. Despite a common name tied to the Civil War era, this mallow is actually a native of China. Both species share the same genus and look similar, but it is their cold hardiness that divides them. Confederate Hibiscus mutabilis is cold hardy to USDA Zone 7, which sets its most extreme limit at 10 to 0 degrees F.
The American Hibiscus moscheutos is sometimes called hardy hibiscus because it is far more tolerant of winter cold. Plants die back for winter but remain root hardy to Zone 5, or at its limit, to -20 degrees F. This is proven by its huge natural range across the eastern states from Massachusetts to Michigan, and south to Texas and Florida.
The plants begin sprouting unusually late in spring, but compensate for their tardiness with rapid growth. Once the soil warms, a good-size root crown will develop amazing proportions in a single season. You can expect them to bloom continuously from mid-July on, slowing with the cooling of autumn nights. They cease altogether when the first frost cuts them down.
Somewhere along the line, the native mallows fell out of style in contemporary gardens. Often the desirability of a new and exotic plant during the 19th century caused gardeners to abandon the old stand-bys in favor of something new. But devoted mallow breeders were not asleep at the switch; their efforts to develop this native into a real dinner-plate showgirl continued unabated, and it has certainly paid off.
The breeders at Pan American Seed have come up with a truly new and improved dinner plate mallow. Dubbed "Luna," this incredible group has transformed the native swamp thing into a Vegas showgirl. These heat-lovers grow to about two feet tall and wide, with dense branching to make a more garden-tidy cultivar than its native ancestor.
'Blush Luna' hibiscus debuted this year, and she is exquisite. Fast-growing disease-free plants produce massive flowers to seven inches in diameter. The color is white suffused with clouds of luscious pink. They may appear delicate, but these plants thrive in the worst heat of late summer. This plant offers welcome color and interest in a flower-scant time of year.
While mallows are most often treated as large bushy plants, Luna is shorter in stature to better suit massed bedding applications. She remains ideal for perennial borders, as hedging and in pots. In the first year, be sure to provide plenty of water to encourage root development. These plants are heavy feeders so keep current on your fertilizer applications. Double up on feeding if blooming ebbs or foliage begins to show yellow.
It is surprising that a native wildflower has evolved into an elegant cold-hardy bloomer. This species is a chameleon that began life as a mud-dwelling swamp thing and has just graduated charm school. Luna is ready to bring her own brand of irresistible southern charm to gardens coast to coast.
(Maureen Gilmer is a horticulturist and host of Weekend Gardening on DIY-Do It Yourself Network. E-mail her at email@example.com. For more information, visit: www.moplants.com or www.DIYNetwork.com. Distributed by Scripps Howard News Service.)