Yes! I use Osmocote Plus on all those plants but I use only a small amount, about half the recommended amount on my rhododendrons. This is because my rhodies are already growing in a rich, compost heavy soil and too much fertilizer makes rhododendrons have softer foliage that can attract disease. I sprinkle about 3 tablespoons around a full grown rhododendron and six tablespoons around a full grown hydrangea. I love my hosta plants to grow huge leaves so they also get a capful of Osmocote in the spring. Sounds like you will have a beautiful garden this summer. Keep growing, Marianne Binetti