Growing rhododendrons in hot weather
A good starting point is to choose plants naturally adapted to hot weather. Rhododendrons native to the southeastern US are good choices. Included are Rhododendron catawbiense var. maximum and R. minus var. minus, as well as hybrids with these species in their background. Other possibilities are species and hybrids in the section Ponticum which have exceptional cold hardiness. It is useful to know that plants that tolerate cold usually tolerate heat, since most books on rhododendrons list only the lowest temperatures withstood by each variety.
Areas with high humidity, such as those near large bodies of water, are ideal for growing rhododendrons. Rhododendrons will not grow without a good source of water. The type of soil, amount of shade, and general temperature of your area all affect the amount of watering rhododendrons must be given. Rhododendrons in sandy soil will need more water will be needed than in heavier loam and clay soil stays too wet. While more frequent watering is essential at higher temperatures, damage may result if plants are sprayed with a hose on a hot day because water drops can act like magnifying glasses and burn the leaves. Spray rhododendrons plants in early morning or after the sun has set to avoid this problem
Trees provide shade, necessitating less watering, but rhododendrons do not like deep shade all day. They will not bloom as freely if they do not get enough light. They prefer broken shade with intermittent sun exposure most of the day with more protection in the hottest hours.