Watering Your Rhododendrons
Newly planted rhododendrons
You should never let the root ball dry out so the plant should be monitored often. A heavy soaking of the plant twice per week should suffice for most conditions. If it's the rainy season, you can curtail your use of the garden hose.
Watering a rhododendron on a daily basis is a "no-no"! You can kill the plant by promoting fungal growth.
Established plants
A good rule of thumb is one inch of rain per week is enough to keep the plant happy and healthy. Established plants can tolerate some lack of water in mild weather. However, in the hot & dry summers you should adhere to the one inch rule.