Q: I see clumps of tall blue flowers called Mexican petunia in my neighborhood. Everyone tells me that they are very invasive and spread rapidly. Are they really that invasive?
A: Tall Mexican petunia, Ruellia brittoniana, isn’t invasive like bamboo or kudzu but it can be pretty “exuberant” when growing in a flower bed with other plants. But there are several varieties of ruellia claimed to be non-invasive: ‘Katie’, ‘Chi Chi’, ‘Bonita’, ‘Purple Showers’, and the “Mayan” series of plants. All yield the non-stop flowering of the tall form but are much less aggressive to neighbors.