Week of August 27, 2001
By Calvin Finch, Conservation Director, San Antonio Water System, and Horticulturist
MEXICAN PETUNIAS, THE GOOD AND THE BAD
The Ruellia genus of plants is an important one for the San Antonio area. Mexican petunia is a ruellia. The genus includes a number of wildflowers and groundcovers that range from being desirable landscape plants to being invasive. The Ruellias in general are called Mexican petunias.
The Ruellia that most of us know (notice that I did not say like), is the full size Mexican petunia. It is a leggy invasive plant that reaches 2.5 to 3 feet tall with blue-violet blooms on the leggy stalks.
Mexican petunia will take over a dry site in full sun quickly through reseeding and underground roots. This is good if you want a tall groundcover to attract wildlife and protect the soil, but not so good if you are trying to grow other types of plants.
Blueshade ruellia is a more desirable selection. It is a fast-spreading groundcover that can grow in shade or sun. It has a quarter-size violet-blue bloom that attracts hummingbirds and butterflies. A planting of 2-inch rooted cuttings on 12-inch centers will cover an area in one growing season. The cuttings can be planted directly into killed St. Augustine grass (Round-up, Finale) and produce a blooming, low water use groundcover for less than the cost of most sods.
Blueshade ruellia is cold sensitive and freezes back to the roots most winters. Katy ruellia is another groundcover ruellia, but it is evergreen most winters. Katy reaches about 14-inches tall with 3- to 4-inch long pointed leaves. It will grow in sun or shade but blooms best in full sun. The blooms are two to three times as large as blueshade flowers and have an orchid look. Katy is aggressive enough to serve as a good groundcover, but is not obnoxious like its larger Mexican petunia cousin.
There is a white-flowered Katy that I think is very attractive but does not sell as well as the blue flowered original. Bonita is the pink flowered version; it also has a redder tint to the leaf. If you have a vacant lot near you or any underdeveloped corners in full sun in your neighborhood, the wildflower, violet ruellia, is probably blooming. The plant reaches about 12 inches on most sites but may be larger. It is an attractive plant with small leaves on sprawly stems. The flowers are violet-blue with five petals. They open in the morning and drop off in the evening. Violet ruellias bloom all summer and fall. Collect their seeds at any time to start a few plants in your wildflower garden. The white-flowered version is also common.
Ruellias are not favorites of the deer. The pesky mammals will eat new growth in a drought but at most times pass up the plants. All of the Ruellias are good xeriscape plants that provide blue flowers (white and pink for some) all summer. They attract butterflies and hummingbirds and are disease and pest free. If you have not tried Katy or blueshade in your landscape, definitely do so. The full size Mexican petunia may work in some situations, but it is too leggy and invasive for my taste.