Ruellia spp.
ruellias
Tropical and subtropical Americas, Africa, and Asia
Overview
Ruellia spp. is a genus of roughly 150 to 300 species of perennials and soft shrubs in the family Acanthaceae, most numerous in the tropical and subtropical Americas and known as ruellias or wild petunias, though they are unrelated to true petunias. Plants range from low, spreading perennials 6 inches (15 cm) tall to upright stems and shrubs reaching 6 feet (1.8 m). The leaves are simple and opposite, often dark green and sometimes flushed with purple. The funnel-shaped, five-lobed flowers open in blue, purple, pink, red, and white, each bloom lasting a single day before dropping cleanly, with new flowers following over a long season from spring to autumn. Many species set seed in capsules that fling the seeds outward when ripe. The widely sold Mexican petunia, R. simplex, self-sows freely and is regulated as invasive in Florida and other warm regions, while native species such as R. humilis stay in tidier clumps.
Native Range
Ruellia spp. is centered on the warm regions of the Americas, with additional species in Africa and Asia. North American natives such as R. humilis and R. caroliniensis grow in prairies, open woods, and roadsides across the central and eastern United States.Suggested Uses
Ruellias are grown in borders, mass plantings, rain gardens, and containers for their long bloom and tolerance of heat, with native species used in prairie and pollinator plantings. They are spaced 12 to 18 inches (30 to 45 cm) apart, with vigorous types confined where they cannot spread into wild areas. The flowers draw butterflies, bees, and hummingbirds through the season.How to Identify
Appearance
Size & Dimensions
Height6" - 6'
Width/Spread1' - 3'
Reaches mature size in approximately 1 years
Bloom Information
Most Ruellia spp. bloom over a long warm season, from late spring until frost in mild climates. Each flower opens for a single day and drops by evening, but plants produce a steady succession of new buds. In frost-free regions some species flower nearly year-round.
Detailed Descriptions
Flower Description
blue, purple, pink, red, or whiteFoliage Description
green, often dark green or purple-tingedGrowing Conditions
Sun Requirements
Requires 6-8 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Most Ruellia spp. grow in full sun to part shade on average to moist soil at pH 5.5 to 7.5 and tolerate heat, humidity, and short droughts once established. The tender species are hardy in USDA zones 8 and warmer and may die back to the roots after frost, returning in spring. Water during dry spells for steady bloom, though established plants withstand neglect. The vigorous species, especially Mexican petunia, spread by seed and runner and can colonize beds and wet ground, so seedlings are removed before they establish. Few pests affect the genus. Cutting plants back hard in spring keeps them compact.Pruning
Cut Ruellia spp. back hard in early spring to remove frost-damaged stems and renew compact growth. Shearing through summer limits seeding and keeps spreading types in bounds. Pull or hoe stray seedlings of the invasive species as they appear.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
early spring
Container Growing
✓ Suitable for container growing
Minimum container size: 2 gallons