Ruellia simplex (formerly known as Ruellia brittoniana), or Mexican Petunia, is a perennial with blue to purple (rarely, pink or white) flowers. They are considered invasive in parts of Florida (and by gardeners who are forced to butcher the ever-enlarging clumps). They are difficult to eradicate once established.
Ruellia (pronounced roo-EL-ee-yuh) is perennial in zones 7 through 10. The narrow plants reach heights of about three feet, with strong stems and long, narrow leaves. Shorter forms are available. ‘Katie’ is a dwarf cultivar (8 inches or less). They prefer moist soil and full sun, but will survive in much tougher locations. These Mexican natives tolerate heat and humidity, and bloom non-stop from mid-spring through fall. Each bloom lasts only one day, but there are many of them. The five-petaled flowers resemble Petunia, Browallia, or Azalea. Flowering is reduced when plants become congested. Lift clumps, divide and replant smaller sections and add fertilizer. Flowering will return to prior levels. Spent blooms produce small seed pods that explode when ripe, spreading seeds over a wide area. ‘Mayan Purple,’ ‘Purple Showers,’ and ‘Mayan White’ are sterile forms; Plants also spread by underground rhizomes, and are easy to propagate from stem cuttings. Remove winter-killed stems to ground level. A light mulch in zone 7 gives longevity insurance in harsh winters.
Ruellia are rarely bothered by insects or diseases, and deer pass them by. Butterflies and hummingbirds visit the flowers. Mexican Petunia’s tolerance for tough conditions and their long flowering period make them a preferred plant for new gardeners. Just keep those invasive tendencies in mind…
A close view of Ruellia flowers
A clump of Mexican Petunia in bloom