Members of the Rhododendron genus, azaleas are frequently confused with rhododendron shrubs. To tell them apart, count the stamens. Azaleas have five or six stamens, while rhododendrons have 10. Azaleas can be either deciduous or evergreen. If yours is deciduous, it will naturally lose leaves in the fall. But there are other reasons why an indoor azalea might lose leaves.
Cause
The most common cause of leaf drop on an indoor azalea is either over-watering or under-watering. Too much or too frequent watering can cause root rot.
Solution
Remove the azalea from the pot. If the roots are mushy, the plant has root rot and should be treated with a fungicide drench. Water the azalea only when a finger inserted 1/2 inch into the soil comes out dry.
Considerations
Some evergreen azalea varieties can also drop leaves. They grow two sets during the season and shed one in the fall.