Plant of the Month: Desert Ruellia

May 13, 2019

Vibrant purple color, lush green foliage, and a long bloom period combine in the form of desert ruellia (Ruellia peninsularis). This Southwestern native thrives in full sun and shrugs off the intense heat in summer. The arrival of spring is greeted by a large flush of purple flowers, which contrast beautifully against the bright green leaves. Flowering will continue through summer and fall with some blooming possible during mild winters. Not to be confused with its more invasive cousin, desert petunia (Ruellia brittoniana), this lovely shrub won’t spread where it’s not wanted.

Also known as Baja ruellia, this purple-flowering shrub is hardy to 25 degrees F. and can suffer frost damage in winter, but quickly recovers in spring. It has a nicely rounded natural growth habit and should not be sheared into a formal shape. Its pruning needs are minimal when allowed enough room to grow to its mature size of 4 feet tall and 4 to 5 feet wide. Once the danger of freezing temperatures has passed, prune back to ½ their size and then allow it to grow back — no other pruning is required. Every three to four years, prune back severely to 1 foot tall and wide in early spring to rejuvenate and get rid of old, woody growth. No supplemental fertilizer is required.

This desert beauty is perfect for the hot temperatures of the Southwest since it thrives in the sun. Photo by AZ Plant Lady. Reprinted with permission.


Because of its tolerance of full sun, desert ruellia can be used in many areas in the landscape, including west-facing exposures with hot, reflected sun. Pair with bougainvillea, orange bells or yellow bells for lovely color contrast. To provide year-round color in the garden, plant desert ruellia along with ‘Valentine’ bush (Eremophila maculata ‘Valentine’), which blooms in winter. Succulents that look nice with this lovely shrub are agaves as well as golden barrel cactus (Echinocactus grusonii). Plant desert ruellia in well-drained soil and in full sun for best appearance. Avoid using it in areas that receive shade for more than half the day or it will reduce the flowering and promote a sprawling growth habit.

The purple flowers of the Ruellia contrast nicely with other plants, such as these agaves. Photo by AZ Plant Lady. Reprinted with permission.


Water – Use It Wisely Editor’s Note: You will also often find two additional popular Ruellia’s used in the low desert. Ruellia brittoniana (Mexican Petunia) is a 2–4 foot tall upright spreading perennial. But, be warned! This plant should be planted in bordered beds to tame their rampant and invasive growth. They spread by seed and underground rhizomes. The Ruellia brittoniana ‘Katie’ is a dwarf horticultural selection that grows only 12–15″ high, works well as a groundcover and is very well behaved in the landscape. Both of these are commonly found in purple, but you may also find white or pink varieties.

Flowering Ruellia
Ruellia brittoniana or Mexican petunia is beautiful but can be invasive.
Katie Ruellia in two colors
Ruellia ‘Katie’ comes in purple, pink, and white.

                                                                                                We have a plethora of low-water-use plants just waiting to be discovered. Check out our Plant of the Month archive to find the right plant for your landscape.

Water – Use It Wisely is proud to feature guest bloggers who write about topics related to water and water conservation. The author of this blog, Noelle Johnson, is an urban horticulturist, Certified Arborist and freelance garden-writer who helps people create beautiful, low-maintenance gardens through helpful advice on her blog She is passionate about teaching people about the amazing desert plants that thrive in our landscapes.