My rhododendron bush is scraggly. Can I trim it back? And when?

After the rhododendron blooms is the best time to cut back. Also each year after it blooms, pinch the blooms off at base of bloom and it will sprout out 5 more times at that one place. This will make it fuller and have more blooms

spring blooming shrubs should be pruned immediately after flowering.

Pinching off the new leaf terminal bud, will stimulate the lateral buds to bloom, creating a bushy plant. I usually do this when I deadhead my bushes. I have some that are 12' high but very bushy. Since its gone so long, you might have to cut it back.

There are you tube tutorials on this. Very informative.