Random plant event: Strobilanthes dyerianus flowers

With some of the stuff we have in the greenhouse, I'm never sure whether I should be pinching off the flowers or letting them go. Strobilanthes dyerianus (Persian shield) is an especially tough call, because it seems like there must be some kind of trick to getting foliage instead of flowers, and I cannot figure out what that trick is. Maybe less light? Anybody know?