When to Prune Rhododendrons
Generally you will want to prune rhododendrons right after the plant is through flowering. Light pruning and shaping should be done every year at the time you remove the old flowers. Because buds on a rhododendron form the previous summer or fall, if you prune in late summer, fall or winter, you may trim off flowers that would otherwise bloom the following spring.
How to Prune Rhododendrons
There is a visible point where the plant growth starts each year called a growth joint. With larger leafed rhododendrons, prune just above this joint because that joint is where the buds that will flower the following spring will be located.
How to Prune Azaleas and Smaller Leafed Rhododendrons
For Azaleas and the smaller leafed rhododendrons, you can pune anywhere along the stem and although you may not be able to see them, these plants have dormant growth buds nearly everywhere.
Pinching out single growth buds just as they grow will cause the plant to immediately produce multiple growth buds for a more bushy plant. This doesn't affect flowering.
Remove Old Limbs
Some limbs of a plant may be shaded out and become weak and die. It is a good idea to remove these, plus other weak limbs that are on the ground or crossing over each other. This will help prevent disesases and pets while increasing air circulation.
Removing old flowers (deadheading) before your plant goes to seed will help improve performance.
Cut at an angle so moisture will run off. You may also want to seal significant cuts with a grafting wax or pruning seal.