They will only fill in where they get light. When rhododendrons are pruned like hedges they become empty in the center. They really should be pruned to remove crossing branches, and admit light and air. It will improve their health and looks. The problem is that few people will spend the time to learn how to prune and to do it. I know a landscape architect in our area that during the off season, will hire out to prune, but he charges the same hour rate for pruning as he does for garden design. Not cheap.

Here is a link that might be useful: How to grow rhododendrons and azaleas.

Thanks very much rhodyman!

I'm going to go read the site right now.

Billy

Nobody admits light and air in nature or any other situation where rhododendrons are growing densely, without pruning. Cut back to below the leggy zone right after bloom, to start them over. Then allow to grow naturally, space permitting, until they are again too tall and stemmy - unless you want to try and work with them. The main point is that flower buds are set on ends of strongest shoots the previous year, so where you do a lot of snipping flowering is liable to be reduced.

bboy, you raise some good points.

To get light to lower parts of the plant there are two ways:
1) remove shade to admit more light. Some rhodies don't like too much sun, so be careful with this.
2) remove dense parts of the plant. Rhododendrons that are pruned into a hedge like the ones that greattigerdane's neighbor has provide their own shade.

You don't need to cut below the leggy zone and remove all of the green part to open up the shade. You only need remove enough of the upper portion to allow light to penetrate to the lower parts.

Pruning itself, will tend to stimulate new growth. This accompanied by more light will produce lush growth on healthy plants.

If you look at horticulture texts on pruning, the goals of pruning woody shrubs is to:
1) remove crossing branches that could rub
2) permit air flow to prevent disease
3) admit light to promote healthy growth

Pruning now, right after bloom, will not remove flower buds because they haven't formed yet. New growth that is stimulated will, in most cases, set flower buds for next year.

Removing lower branches of trees will admit more light which prevents leggy growth. Too much shade induces leggy growth, meaning a few long vertical branches usually with sparse foliage except on the top.