If you have noticed a plant in Tucson and Green Valley nurseries called Ruellia, you might be wondering if this is a good choice for your desert landscaping. It depends on your expectations, and which variety you are considering.
Ruellia brittoniana comes in different colors. The common flower color is purple, but there is a pink and white species also available. These are all higher water use plants, and need care to look their best. Although root hardy to 15 degrees, that translates to the top being frost tender, and this plant will suffer frost damage in cold winters that will need removing. Consequently, especially in the colder areas of Green Valley, this plant looks ratty during the winter months.
Another Ruellia species, called Desert Ruellia, is only hardy to 25 degrees, so is not suitable for the Tucson and Green Valley areas.
Instead of buying a fussy plant, it makes sense to choose one with far less problems. The Penstemon species is a reliable wildflower, and with so many to choose from you can have hummingbird flowers from late winter to early summer. Also consider other perennials such as Red Salvia and Mexican Oregano, both which flower nearly 9 months out of the year and are cold hardy.