Name: Ruellia caroliniensis
Wild petunia, Carolina ruellia
Zones 7/8 to 10
12 to 18 inches
Indeterminate; clump forming
Cottage-garden borders; meadow and wildflower gardens; lawn conversion projects
Lavender-blue flowers late spring to early fall on sturdy stems; heat, drought and salt tolerant; low-maintenance; easy to propagate
Funny how things work out. Ruellia caroliniensis arrived at my coastal North Carolina home a decade ago in three 2½-inch pots from Woodlanders Nursery in Aiken, S.C. Subsequently, I spent hours every summer unsuccessfully trying to keep it contained in the border and out of the lawn. Then last spring, Oak Island's budget-busting sewer installation went operational, meaning I could no longer afford to water my grass. As a consequence, the stalwart green foliage brandished on sturdy heat-, salt- and drought-defying stems sprinkled with cheerful little lavender-blue blossoms became welcome - nay, encouraged - to spread wherever it wanted.
The genus Ruellia is named for Jean de la Ruelle (1474-1537), personal botanist and physician to France's François I. Although "petunia" figures in the common names of most of the 150 or so species and their flowers bear some rudimentary resemblance to one another, ruellias are not petunias: they belong to the acanthus family.
Highly adaptable, Carolina ruellia prefers full sun to light shade and well-drained soil, but pretty much tolerates whatever environment it finds itself in, making R. caroliniensis a natural for managed wildflower gardens and meadows, cottage-type borders, and lawn conversion, diversification and naturalization projects. It's not so good for formal designs because, like all the Acanthaceae, its seed capsules explode, spewing seeds to impressive distances from the mother plant.
Today's time-restricted gardeners can't ask for a more easygoing plant. Emerging from dormancy as early as February here in southeastern North Carolina, the first 1-inch-wide blooms open around the end of April. Individual flowers last only one day, but their production continues steadily, although seldom prolifically, into October. In shady locations, growth is leggier and bloom sparser. As for maintenance, all you need do is cut down the dead stalks (or not) once they go grey and crunchy. Fertilize only if you wish to encourage rampant tendencies.
Propagation by seed is a breeze: in fact, some deriders of the species say it self-sows with too much abandon (to which I can testify, from the days when I strove for a perfectly monocultured lawn). Still, Ruellia caroliniensis plays well with its neighbors. In my yard, it has shared about 5 square feet with a clump of Iris tectorum for 10 years without apparent detriment to either.
Photos courtesy of Kathy Fitzgerald
Nor did wild petunia harm the centipedegrass it seeded itself into. It stayed at about the same height as the lawn - 2 to 3 inches - and tolerated mowing very well, despite curtailed flower production.
The pleasantly mid-green colored foliage is ovate to lanceolate and slightly hairy on the reverse. Pubescent stems never require staking, even in the dreadful heat and humidity of southeastern summers.
Native to the southeastern half of the United States (New Jersey to Florida, southern Pennsylvania to Nebraska), Carolina ruellia is reliably hardy in Zones 7/8 to 10. While similar to R. humilis (short ruellia), R. caroliniensis' leaves have petioles, and its stalks are longer. Not that it matters; I've yet to see either commonly available in the trade. Funny how things work out.
Fitzgeralds Gardening, Oak Island, N.C.