Q: I would like to know when to prune my Mexican Petunia so it will produce more flowers.
A: Mexican Petunia, Ruellia brittoniana, also called Britton’s wild petunia is classified as an invasive for Florida according to the Center for Aquatic and Invasive Plants (http://plants.ifas.ufl.edu/ruebri.html). It is sold in nurseries everywhere but it easily escapes into wildlife areas and therefore is not the best choice for a landscape plant. Like many perennials, it will die back when cold weather comes but will quickly return in the spring. So to answer your question, we would not want you to prune it back to encourage it to produce more flowers and therefore more seed. It might be best to allow it to go dormant during the winter to avoid over-production of seeds