Rhododendrons like a lot of water. To save the soil from evaporation of water, you can attach a layer of mulch around the rhododendron plants. As covering layer, you can use bark mulch, shredded shrubs or even leaves.
Remove spent flowers. They weaken the plant and can reduce flowering in the following year.
If you want the rhododendron to grow more densely, you need to prune the branches. The best time to do this is after flowering. This way, the plant has enough time to form new buds.
For pruning you should use sharp loppers or secateurs. You can cut off twigs at branch forks or single branch stumps. Also remember to take a look into the rhododendron bush. Inside, branches often grow back and forth so that gentle pruning is also useful here.
(Image: © Aleksey Stemmer - Fotolia)