Mexican Petunia (Purple Showers) Plant Profile

A dewey Mexican petunia bloom or Ruellia brittoniana in Florida
Diane Macdonald / Getty Images

The Mexican petunia (Ruellia brittoniana) is a beautiful addition to a flowering backyard retreat. As a hardy perennial (you only need to plant them once), the Mexican petunia is one of several desert plants that are recommended for warm, dry climates. They are inexpensive, low maintenance, and drought-resistant. Also known as Purple Showers, the Mexican petunia's flower petals are most commonly a vibrant violet color, but they can also be pink or white. Like daylilies, they only bloom once a day, but continuously bloom throughout the summer.

Botanical Name Ruellia brittoniana
Common Name Mexican petunia, Purple Showers
Plant Type Flowering evergreen perennial shrub 
Mature Size 34 Feet
Sun Exposure Full and part sun
Soil Type Any
Soil pH Any
Bloom Time May to November
Flower Color Purple, Pink, White 
Hardiness Zone 811
Native Area Mexico 
Blooming Mexican Petunia
_jure​ / Getty Images  
Mexican petunia flowers in garden
 GeorginaCaptures / Getty Images 
Pink and purple mexican petunia flowers
Achisatha Khamsuwan / Getty Images 

How to Grow Mexican Petunias

Mexican petunias are evergreen flowering shrubs, meaning they remain green over the winter when not in bloom. As long as you follow a basic desert garden to-do list and keep to a conventional summer watering schedule, you should have no problem raising bushels of these purple blossoms.

The Mexican petunia plant is a fast grower and is used successfully against block walls or to surround and camouflage unpleasant looking electrical boxes and air conditioning units. If growing around an appliance, make sure you leave enough room on one side so it can be accessed for maintenance.

When given ideal growing conditions, Mexican petunias are not very susceptible to blight. There is also no major concern when it comes to pests.

Light

Mexican petunia bushes take full sun—the more direct sun they receive, the more flowers will bloom. They can withstand shade and partial shade but will be less productive if planted in these areas.

The color of the stems will vary depending on the light conditions—the more light the plant receives, the more purple you will find on their stems. In shadier areas, the stems will present as a solid green.

Soil

While Mexican petunias will grow in a variety of soil types, they prefer to be planted in well-drained, fertile soil. They grow and spread extra quickly in marshy soil, or next to rivers and lakes. When it comes to soil pH, these plants will survive in alkaline beds, but they most prefer neutral to slightly acidic environments.

Water

Even if you live in an arid climate, you can still raise a fantastic garden full of bright and showy Mexican petunias. They're unique in that they're drought resistant and yet they also survive floods. They do benefit from occasional watering in dry climates but can go without for long stretches of time.

Temperature and Humidity

Mexican petunias are a favorite plant in the desert, but they also grow well in humid climates. They do not survive in the cold, yet they can still be enjoyed as summer annuals in areas that experience low temperatures in the winter.

Fertilizer

While it's not mandatory, Mexican petunias benefit from the addition of manure, fertilizer, and compost in their growing areas. In the springtime, you can use a garden rake to mix in a fertilizer of choice into the top 2 inches of the soil surrounding the plants.

If you're planting Mexican petunias for the first time, you may want to use a shovel or garden tiller to loosen and turn over the soil before planting, sprinkling in compost or manure as you work. To improve drainage in moist beds, consider adding a little sand to the mix.

Potting and Repotting

Mexican petunias can be grown in pots. As long as they're placed in a sunny spot, they grow well in indoor pots and outdoor planters alike. As a fast-growing shrub, they may need to be repotted more frequently than other plants.

In addition to pots, you can also experiment with more creative vessels like ladder planters, wagons, or even an old bathtub. Since they grow to be a shrub, medium to larger-sized containers work best.

Propagating Mexican Petunias

Mexican petunias will spread quickly and naturally—sometimes aggressively— especially in moist climates. The shrub is considered invasive in the state of Florida and it's on the watch list in several others. It spreads by seeds that can sometimes reach up to 10 feet away from the original plant, as well as through thin, underground roots called rhizomes. Since they can spread at a fast pace, you may consider growing them in a more contained area so they don't end up taking over your entire lawn.

If you want to speed up the propagating process, you can create new plants from tip cuttings. Once you've taken your desired amount of cuttings, remove the buds, flowers, and lower leaves from the stems. Dip the ends of each stem in rooting hormone, and then plant in pots filled with peat moss and soil. Once they take root (usually after a few weeks), you can add the plants to your yard.

Transplanting Mexican petunias is best done in the fall before they go dormant in the winter. Once established in their new location, they should grow as normal and perk up when temperatures increase in the spring.

Varieties of Mexican Petunias

If you're concerned about excessive spreading, you can opt to plant a sterile variety of Mexican petunia. In fact, the wild variety is not often sold since it can become so problematic. "Katie" is a popular dwarf cultivar because it doesn't produce seed pods and therefore is not considered invasive.

Dwarf mexican petunia
Abdecoral / Getty Images 

Pruning

Mexican petunias do benefit from pruning, especially if they're grown as a hedge. Cutting back the stems after flowering will encourage new growth and even more blossoms. They don't get very tall—just 3 or 4 feet high—so keeping them trimmed back can be done usually without a ladder or other special equipment.

Growing From Seeds

Mexican petunias can be started from seed, planting them inside several months before the growing season. Or, you can try planting the seeds directly into the ground. If you want to harvest seeds from your existing plants, remove the seed capsules once they turn brown in the fall. Let the seeds dry out and then plant them in a new area in the springtime.

Mexican Petunias vs. Petunias

When you first see a Mexican petunia, you may mistake them for the common annual petunia as their flowers are quite similar. While they do share this resemblance, the two plants are not closely related. Upon a closer look, you may notice the long and thin leaves of the Mexican petunia are quite different from the furry, full and pointed leaves of the annual petunia. Mexican petunias are also a shrub, featuring woodier stems and growing much taller than their look-a-like.