This is my first experience with rhododendrons. I planted 4 purple gems in May. I got them in the nursery after they were done blooming. They have been growing great all summer. Today I noticed a flower opening on one of them. I looked closer at all four and they all have a good number of flowering buds swelling and getting larger. It looks like all four may bloom before fall. Is it common for rhododendrons to flower twice in one season, especially in August?
It happens, though not too often, and mostly due to weather conditions, watering, stress, etc. Often they don't really flower well when this happens (if the flowers ever actually open), and then they flower less than normal the next spring.
The other buds might just be normal summer bud-set for next year. some start making new buds within a few weeks of blooming (Boule de Niege is an example).