Q: I’m considering planting Mexican petunia by my mailbox. However, I am reading where it can be very invasive and do not want it to overrun the azalea and hostas I have there now. What are your thoughts?
A: In my experience, the tall form of Mexican petunia, Ruellia brittoniana, will certainly spread quickly to fill a given space. It reproduces by seed as well as with underground runners. If nearby plants are short, this ruellia will shade them.
On the other hand, there are at least three varieties of ruellia that are dwarf forms: ‘Katie’, ‘Chi Chi’ and ‘Bonita’. All yield the non-stop flowering of the tall form but are much less aggressive to neighbors.
On the other other hand, (CQ) Florida has named ruellia an invasive plant with potential to adversely affect native habitat. My advice is to use caution with this plant and remove unwanted seedlings as they occur. Ruellia tolerates wet spots very well. I have a clump growing in a pot submerged at the edge of a shallow pond.