Shrub
Desert ruellia
Ruellia peninsularis · Acanthaceae
Also called: Baja ruellia, Desert petunia
Desert ruellia (Ruellia peninsularis) is a low-water shrub well suited to Tucson and the low desert. It grows to 3-4 ft H x 4-5 ft W in full sun to partial shade, with a moderate to fast growth rate. Expect purple to violet-blue blooms spring through fall.
Desert ruellia at a glance
- Water use
- Low (established)
- Sun
- Full sun to partial shade; flowers best in full sun, appreciates some afternoon shade in hottest sites
- Mature size
- 3-4 ft H x 4-5 ft W
- Growth rate
- Moderate to fast
- Bloom
- Purple to violet-blue, Spring through fall (heaviest spring flush), with sporadic bloom in mild winters
- Cold hardiness
- Hardy to about 25-28 F; foliage damaged by hard frost but recovers in spring; USDA zones 9-11
- Soil
- Well-drained soil; tolerant of native desert and improved soils; not particular about pH
- Native range
- Baja California and Sonora, Mexico (not native to the U.S./Arizona)
- Best used as
- Mass plantings and informal hedges, Foundation and accent shrub, Pollinator gardens, Color in low-water landscapes, Median and commercial plantings
- Wildlife
- Flowers attract bees and butterflies; provides cover for small birds. Foliage is generally not browsed by rabbits or javelina.
- Toxicity
- Not known to be significantly toxic to humans or pets.
How to grow Desert ruellia in Tucson & the low desert
Watering
Water deeply but infrequently once established, roughly every 2-3 weeks in summer and monthly or less in winter; tolerates more water with more lush growth and bloom.
Fertilizer & nutrients
Generally not needed in reasonable soils; a single light application of balanced or slow-release fertilizer in spring can boost growth and flowering if desired.
Pruning & care
Has a naturally rounded form; avoid shearing. Cut back hard in late winter/early spring to remove frost damage and rejuvenate; an occasional light trim controls size and tidies after bloom flushes.
Notes
Tough, heat-loving Sonoran (Baja) shrub valued for its long season of purple bloom and bright green foliage. Each flower lasts a day but plants flower in repeated flushes. Drought-deciduous and frost-deciduous; quick to releaf. Reseeds modestly.
Sources: AMWUA Landscape Plants for the Arizona Desert (Baja Ruellia); Water Use It Wisely; University of Arizona LAR 520 plant database; Arizona State University (Martin) plant database