Answer: I dont' think it's the weather, but more likely a combination of transplant shock and a need for more water until the roots become established. While it's true that bougainvilleas tend to bloom better when soils are dry (in their native habitat they typically bloom right after a drought, just as rainfall begins), they still need some TLC while they become established. I'd water more frequently for the remainder of the season, soaking the soil deeply once each week. Here are some guidelines for healthy bougainvilleas:
Bougainvilleas are tropical vines native to Brazil. They produce masses of showy blooms which are actually bracts that look like bits of colorful paper. The common name is Paper Flower. Bougainvillea captures the essence of the tropics with lush foliage and electric, sensational colors. But don't be misled by this popular plant's exotic color and form, it's actually easy to grow.
Similiar to Roses, Bougainvilleas grow and bloom in cycles. Bloom cycles are usually about 5-6 weeks, then all the bracts fall. Between this cycle, new leaves/stems grow. If the plant has been grown properly you can expect a new flush of bloom after vegetative growth. Here in California, bougainvilleas bloom best in Spring, Fall and Winter. Long days in Summer seem to retard bract formation. However some varieties, still bloom well even in the Summer to make a nice display if properly cared for and fertilized.
Protect from high winds. Freezing temperatures will damage plants so when the temperature falls to the low 30's be sure to protect the plants.
Bougainvillea can be lightly pruned or pinched after each bloom cycle when the old bracts fall. Pruning usually results in a more compact, plant, which will grow faster and eliminate the need for frequent repotting. Prune just above a leaf joint, leave no stubs.
Bougainvillea can be fertilized every five or six weeks after each bloom cycle. Potassium nitrate type fertilizers aid in bloom formation. Use of soluable liquid fertilizers requires more frequent fertilizing and sometimes results in overwatering. A good slow release granular is best.
Bougainvillea should be kept evenly moist. The soil should be allowed to dry somewhat between watering. Do not keep soil soggy. Blooming can be enhanced by allowing the foliage to wilt slightly between waterings.
This information is for established plants, so be sure to water deeply once each week until the roots of your plants become established. You can prune away the dead plant parts - healthy roots will replace the lost stems and foliage.
Hope this information is helpful!
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