Powdery Alligator-flag

Linger for a few minutes beside the South Lawn pond in the Historic Gardens or the Virtue Peace Pond adjacent to the Doris Duke Center, and you’ll be impressed by the number of bumblebees, carpenter bees and dragonflies visiting the powdery alligator- flag (Thalia dealbata) for a quick meal or a perch. With its long, swaying stalks and bright purple flowers, this plant stands out even at a distance, waving in the wind just like a flag on a flagpole—fortunately, no alligator required.  

Powdery alligator-flag is named for the white water-repellant coating on its leaves and stems, which helps keep it from drowning during periods of high water. It is also known as the hardy canna for its superficial resemblance to the true cannas (Canna spp.), a group of showy herbaceous perennials with a similar appearance (canna is Latin for “reed”). It’s a member of the Marantaceae, or arrowroot family, a group of mostly tropical American species known as “prayer-plants.” True to its names, powdery alligator-flag raises and lowers its leaves with the sun as if in prayer, or as a flag would be raised and lowered at dawn and dusk each day.

Native to southern and central North America, powdery alligator flag grows in water up to 18 inches deep, preferably in rich, loamy soils in full sun. The plants primarily reproduce by creeping rhizomes, quickly forming dense colonies that help prevent shoreline erosion and filter toxins and sediments to improve water quality. They are also important wildlife plants—in addition to supporting bumblebees, butterflies, other native insects, and even hummingbirds, with the nectar from their flowers, their dark brown seeds are eaten by ducks in the fall during migration.  

For a plant with such a tropical look, powdery alligator-flag is impressively hardy, capable of surviving below-freezing temperatures if the roots are kept immersed in 1.5 to 2 feet of water. Even if the water freezes, it won’t be harmed, as any ice will only form on the surface and serve as an insulating barrier to the fluctuating temperatures. This allows for the plant to be grown as an ornamental far outside its original range, preferably in plastic tubs to keep it from naturalizing.