A: You need to be meaner to your plants. Don’t love them so much, and in particular, don’t water them so much!
Bougainvillea thrive in hot, dry climates, and you need to emulate that. Water bougainvillea about half as much as you typically have. Check the soil moisture in your container with your finger – if it’s wet to damp, leave it be. Water only when the leaves begin to droop slightly. Fertilize with a lower-nitrogen than we’d typically recommend for North Texas – Carl Pool’s BR-61 gives us excellent results.
And, of course, do grow your bougainvillea in a container if you intend to keep them year to year. They’re just not winter hardy for us, but generally worth the effort!