A Mexican petunia, or Ruellia brittoniana, is easy to grow under most conditions. These plants will produce blooms in almost any type of soil, and are resistant to both drought and wet conditions as well. Mexican petunias are perennial shrubs, which can grow as tall as three feet, but in cold climates Mexican petunias can be grown as annuals that must be replanted every year. There are also some dwarf species available, which will grow only to less than one foot. With minimal care and supervision, these plants produce attractive, tubular flowers which are generally bluish or purple in color, and similar in appearance to common petunias—even though the two plants are not related. These plants are very attractive to butterflies, which makes them popular choices in many yards.
Tip: Gardeners seem to either love Ruellia, or dislike its invasive nature. In some areas of the country, a sterile version of Ruellia, which will not re-seed, can be found at nurseries and garden centers.
Soil and Planting Site
Mexican petunias, also known as desert petunias, produce more flowers the more sunlight they have, so choose a sunny spot in your yard. Though Mexican petunias are highly adaptable to most soil types, they grow better in fertile soil that is well drained and capable of retaining the required amounts of moisture. Amend the planting spot with some mature compost, and remove all weeds four to five weeks before planting. Soil drainage can be improved by incorporating some sand and thoroughly mixing it in with the soil. The roots are very easily formed in such a planting spot, in the right temperature and climate. The best time to plant Mexican petunias is early spring, when there is no chance of frost. Once established, the plant will bloom profusely throughout the warmer periods of the year.
You can easily propagate these plants with cuttings, seeds, or by divisions.
Once established, Mexican petunias are very hardy, and can survive for long spells without water. However, young plants need regular watering. You can also grow these plants indoors in pots, provided they have a sunny location. Indoor plants must be watered regularly as well during hot weather. Keep them away from any heat vents and electrical equipment.
In the winter, indoor Mexican petunias must only be watered when the soil shows signs of drying. These plants are highly resistant to most pests and diseases.
In warmer climates, Mexican petunias can grow rapidly and propagate themselves by way of seeds. In some areas, this plant is considered an invasive species because they can spread very fast, taking over the yard if not controlled. If you feel that these pretty plants are taking over your yard, you can easily pull out the required number of stems. These shrubs also need their woody and tough stems regularly pruned to maintain their shape and appearance.
If you want more of these beautiful flowers in your backyard, cutting stems halfway after flowering will result in the growth of several more stems and flowers. In colder climates, the foliage will be damaged by frost, in which case the damaged parts must be removed and disposed of promptly to avoid infection.