The Ruellia brittoniana, commonly called the Desert Petunia, is not related to the garden petunia we are all familiar with. The R. brittoniana originated in Mexico, and it is sometimes called the Mexican Petunia. This tough perennial can be invasive as it easily spreads by seed and rhizomes. Since I wanted to have a stand of it in one area of my garden, I’ve appreciated its ability to self-sew. Invasiveness is not so much a problem in our Arizona soils as in other areas where it grows (USDA Zones 9-10) since our desert soils are much lower in organic matter.
The R. brittoniana comes in several colors, including purple, blue, pale pink and white. I’ve had the pale pink variety, but much prefer the lilac blue of the plants I currently have. It flowers from spring until the first frost. In a warm year, I have flowers year-round. If we do have frost, the plant looks bad, so I cut it back to six inches and it comes back better than ever.
There is also a dwarf variety of the R. brittoniana with blue-purple flowers called ‘Katie’. The dwarf variety also comes with the same range of colors as the regular Ruellia. I also have ‘Katie’ in my garden. Both types are easy care and both are drought-resistant. The dwarf variety does not spread as easily as the taller R. brittoniana, so it is popular in smaller gardens. The dwarf variety makes a great container plant. It grows to about one foot tall and two feet wide and deadheading is not necessary.