You can cut them back mercilessly and they will return! It is the nature of that ruellia to grow tall and upright. You can cut them now for some benefit, although they won't grow much when winter arrives. In your climate they may remain partially green over winter but probably won't bloom much if any. During a cold spell they may even be killed to the ground. If you do a major cutback in late winter, even to a few inches high, they will return quickly as warm weather returns.
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