Hi. I have grown a ruellia brittoniana/simplex plant in a large pot with ordinary potting soil for two years. In the summer it goes outside in the sun and in the winter I have put it in a bright spot at normal room temperature. It doesn’t get around to flowering until the very end of the summer. Should I be giving it more light (or less) during the winter? Would it overwinter better in a cooker place? Thanks for the help.
Thank you for your inquiry concerning your Mexican petunia (Ruellia brittoniana aka R. tweediana). Although considered to be a somewhat invasive perennial in the Southeastern U.S due to its exploding seeds, it is used as an annual north of the U.S.D.A. zone 8. More than likely you have the cultivar ‘Purple Showers’ which is a sterile plant, as a result it will not produce seeds. Although each flower lasts for only a day, it is a prolific-blooming and easy-care plant during the summer months. Ruellia prefers moist well-drained soil sited in an area where is receives full sun ( 5-6 hours).
The following links provide more information on this lovely annual:
https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=c952
https://www.finegardening.com/mexican-petunia-ruellia-brittoniana-purple-showers
When bringing your plant indoors you need to ask yourself- how much light did your outdoor plant need? Did you locate your plant in full sun, or did you have it in part shade? In all cases you should try to mimic the same amount of light when you bring the plants indoors in the winter. Full sun plants should be closer to windows than those requiring shade. If necessary, you can rotate their location a little.
Another important factor is to avoid placing them in a location where they will not experience extreme temperatures. As a result, avoid cold drafts from a window or drying heat from your furnace vent.
One of our archived posts titled Bringing plants indoors for the winter gives additional step by step instructions for successful transition to your indoor environment.
Good Luck!