July, August and September in Texas are the months that put plants to the real test! If they can survive the unrelenting heat, lack of rainfall and the blistering sun, then we know they're keepers. It's even better if they flower constantly and are perennial. Such qualities do exist in Verbena rigida 'Santos.'

This species of verbena from South America is unlike any I've ever grown before. The long, serrated green foliage doesn't resemble other verbenas, and it has tuberous roots. The tuberous roots system not only helps this plant to be exceptionally drought-tolerant, but also a hardy perennial to Zone 7.

Santos has 1-inch lavender-purple flower clusters held on 1-foot-tall stems. Flowering is heaviest in spring and fall, but this plant is almost always in flower. Unlike other verbena species, this one is very resistant to powdery mildew, which usually wipes out any other verbena during our wet spring and fall rains. The foliage isn't favored by rabbits or deer.

Santos is not picky about soil type - it thrives equally well on clay or sandy soil. One thing to be cautious about: This verbena is vigorous! It can spread to 4 feet across in one season. I would not call it invasive, but don't plant less aggressive plants in its immediate vicinity. Personally, I like tough plants that, instead of dying in summer, spread and stay in flower!

During winter, cut this verbena completely to the ground. In spring, it will resprout quickly and flower by April. Also, if it begins to look rough in summer, just shear it right off at the soil level, it will be back in flower within days!

You should be able to find Verbena rigida 'Santos' online with a little research either as seed or small plants. So far I haven't seen it in local nurseries, but they may be able to order it for you.

About the author: Jimmy Turner is the Director of Horticulture Research at the Dallas Arboretum, visit www.dallasplanttrials.org for more information on his trials. For more plant profiles by Jimmy, subscribe to Neil Sperry's GARDENS Magazine.