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Tuesday - July 17, 2007

From: Paris, France
Region: Other
Topic: Non-Natives
Title: Care of Rio Grande Wild Petunia
Answered by: Barbara Medford and Joe Marcus


I have bought the Rio Grande Wild Petunia, Ruellia davisiorum. How should I look after it?


The really wonderful thing about planting native plants is that they are going to be easier to care for because they are already adapted to the environment. However, while this plant is native to our Central Texas environment, we note your question came from France, so in your case, it is a non-native and may require some special provisions for it to flourish. France, like Texas, covers a wide area and includes many divergent climates, soils, elevations and ecologies.

We would hate it if any of the native plants that are so dear to us here in Texas became nuisance, or worse, invasive species in Europe. So we ask that you take particular care to make sure that your Ruellia does not escape from cultivation.

Since we don't know which area of France you may be gardening in, we can only give you the information on where Ruellia davisiorum (Rio Grande wild petunia) occurs naturally and tell you a little about the conditions there. This plant occurs naturally only in extreme South Texas and in adjacent Mexico. The "wild petunia" in the name refers to the fact that the blooms of all ruellias resemble those of Petunia, a genus of South American natives much-hybridized to produce plants of nearly every color but orange. Petunias are not closely related to ruellias.

The environment in Rio Grande Wild Petunia's native territory is generally desert shrub savannah. Soils are dark, calcareous stony clay and clay loams. Altitudes average about 2500 ft. above sea level, and temperatures average from 35 degrees in January to 97 degrees in July. Average rainfall is 17 inches a year.

Just because the native range of Ruellia davisiorum is relatively quite small doesn't mean it's the only place it will grow. There are a number of different types of ruellias, and all are pretty tough and adaptable. For example, Ruellia occidentalis (western wild petunia), is native to larger parts of Texas and therefore not quite such severe conditions. Native habitats of ruellias generally are dry, rocky woods, chapparral hills and flats on the Edwards Plateau and the Rio Grande plains. They are perennials plants. Their light requirements are light shade to shade, but in an area where the sun isn't quite as fierce as it is in Texas, they can probably tolerate more sun. Ruellias' growth habit is as an herb or a subshrub, the soil moisture can be moist or dry, and they are heat and cold tolerant.

We hope this has given you enough information to transform some of your garden into a "little bit of Texas." Best wishes.


From the Image Gallery

Rio grande wild petunia
Ruellia davisiorum

Western wild petunia
Ruellia occidentalis

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