How To Grow And Care For Ruellia

Though most common in Texas, they're quickly making inroads into the rest of the South, especially among gardeners who want lots of bloom with little fuss. The flowers resemble small, thin-textured petunias, although they are of no relation. This shrubby perennial grows up to 4 feet tall and blooms in early summer with purple or blue flowers that will attract butterflies and hummingbirds. Ruellia blooms from early summer through fall, and it’s hardy in Zone 7 (USDA) and below. These plants resist damage by browsing deer.

Ruellia is easy to grow in full to partial sun, and it grows equally well in wet soil and dry soil. In fact, it can be found in traffic islands or growing wild by the road where it receives no care and continues to grow well. Because it needs so little, ruellia can spread with ease. It forms large clumps with spreading roots, and its seed capsules scatter seed. In wet and unmanaged areas, it can be invasive, and is counted among invasive plants in Florida. 

Here is everything you need to now about growing and caring for ruellia in the South.

Plant Attributes

Common Name	Mexican petunia, wild petunia, Texas petunia, Britton’s Wild Petunia, Mexican bluebell
Botanical Name	Ruellia brittoniana, R. malacosperma, R. tweediana
Family	Acanthaceae
Plant Type	Perennial
Mature Size	3-4 ft. tall
Sun Exposure	Full, partial
Soil Type	Loamy, sandy, moist but well-drained
Soil pH	Acidic, neutral
Bloom Time	Summer, fall
Flower Color	Blue, purple
Hardiness Zones	Zone 8-10 (USDA)
Native Area	North America, South America, Caribbean

Ruellia Care

Ruellia is a hardy perennial grower, thriving in nearly any growing condition that you might throw at it: wet, dry, hot, hotter, sun, partial shade. Ruellia grows well in our humid Southern climate and likes regular moisture and well-drained soil, growing best in Zone 7 (USDA) and below. 

Light

When planted in full sun, ruellia will flower profusely. It grows well in partial shade, too, but will produce fewer blooms.

Soil

Ruellia grows best in neutral to acidic soil that drains well. This plant is not picky, and  it will grow in most conditions.

Water

Ruellia is known to survive and thrive in spite of flooding or even drought conditions. But for best results in your garden, provide regular water in soil that is rich and well-drained.

Temperature and Humidity

Ruellia grows well in our hot, humid Southern climate, thriving in sunny locations, plenty of heat, and humidity. They aren’t cold hardy, and won’t perform as a perennial above Zone 7 (USDA). Here, they make a great potted annual.

Types of Ruellia

Ruellia Elegans 'Ragin' Cajun: Plant this perennial in LS, CS, TS Zones 8-11 (USDA). The species in native from Brazil to Chile and grows 4 ft. tall and 8 ft. wide. Scarlet flowers bloom late spring through fall. Needs little to moderate water after it’s established. Plant this variety as an annual in US, MS Zones 6-7 (USDA).

Ruellia Humilis ‘Blue Shade’: This shrubby perennial is native to the central United States and grows 12 ft tall and wide with oval to lance-shaped leaves 14 inches long. The 2-inch long blue flowers bloom early summer into fall. ‘Blue Shade’ is a low-growing (6-10 in.) and wide-spreading form with lavender-blue flowers. This selection is popular in Central Texas as a ground cover for light shade.

Ruellia macrantha ‘Pink Wild Petunia’: You’ll find this shrub in CS, TS Zones 9-11 (USDA) growing up to 3 ft. high and wide with oval, dark green leaves. Clusters of 3-4 in. rosy pink flowers blooms in late fall and through the winter in the Tropical South. This variety grows best as a container plant. Provide shelter during frost.

Ruellia Malacosperma ‘Mexican Petunia’: This shrubby perennial is native to Mexico and often confused with Ruellia tweediana, but its leaves are a little shorter and wider. This hardy plant will grow well in dry or wet soil, grows 3 ft tall, and blooms with light purple flowers in summer. ‘Alba’ (sometimes sold as White Flower Form) produces hundreds of white blooms June through September.

Ruellia Tweediana (Ruellia Brittoniana) ‘Willowleaf Mexican Petunia’: This shrubby perennial grows in LS, CS, TS Zone 8-11 (USDA). This native naturalizes and can be invasive. To control growth, contain it to edging. Light purple flowers bloom throughout the warm times of the year. ‘Chi-Chi’ bears soft pink blossoms. ‘Katie’ is a noninvasive dwarf (10-12 in tall). Other dwarf varieties include ‘Colobe Pink’, pink flowers; ‘Strawberries and Cream’, lavender blossoms and white speckled leaves; and ‘White Katie’, similar to ‘Katie’ but with white blooms.

Potting and Repotting Ruellia

There are two good reasons to grow ruellia in a pot. The first is to control the plant from spreading. The second is to enjoy ruellia when you’re just outside its recommended growing Zone. In this case, planting ruellia in a pot means you can move it to a sheltered location during a frosty spell. This plant grows well, so if you choose to pot it, be prepared to repot it once it fills the pot. Choose the next size up, about 2 inches larger and gently move the plant to its new pot.

Overwintering Ruellia

Overwintering ruellia is not cold-hardy so protect it during any surprise cold spells.

How to Get Ruellia to Bloom

Beyond planting ruellia in a sunny location, which is the best way to encourage blooms, you can also practice deadheading, or pinching off the spent blooms. This tells the plant to redirect its energy into making more blooms. Each flower lasts about a day, but the quantity of blooms will never leave you wanting for more. These purple blooms resemble the petunia, although they are of no relation, and do not have a fragrance.

Common Problems With Ruellia

Ruellia needs so little and spreads with ease. It forms large clumps with spreading roots, and its seed capsules scatter seed. In wet and unmanaged areas, it can be invasive, and is counted among invasive plants in Florida.