Does anyone know how and when you trim a rhododendron in the northeast US?

Question

It is huge and I am clueless

Answer 1

If you can wait until after it blooms next year, you will probably do a much better job. It already has the dormant buds for next year, and if you prune now, you will be removing next year's flowers. After it blooms, you just snap the dead flowers off, because the dormant buds are just below the current flower.
If you need to reduce the size of the plant over all, you would likely be better off removing a few of the oldest and most poorly placed branches all the way back to the base of the plant. If that's what you intend, you should take this on as a gradual process over several years, never removing more than 20 - 25% of the plant at any one time. More than that will shock the plant and impact its health.
If it has completely outgrown the area it's in and gradual pruning doesn't seem right for your situation, you might transplant it where it has more room, or offer it to someone who will come and dig it out for their own use. Then replant, using some consideration to the ultimate size of the plant. They always look so little in the nursery pots, and most of us do a poor job of imagining just how large they are going to get.

Answer 2

You don't mention where it is located, why you want to trim it, or, approximately how tall. But the trick to these is never trimming too much off. Otherwise, you stand the risk of no blooms for the next year... or more.

Any trimming done should be done shortly after they finish blooming for the year. They bloom on the previous year's growth. If your plant is several feet to high... you would be wiser to relocate it in the fall and replace it with a younger one.

Answer 3

They need to be trimmed right after they bloom. Or you will be cutting off next years blooms. If you don't mind no blooms next year then anytime.

Answer 4

During the fall, and at the stem.