Azalea’s and Rhododendron’s love acidic soil with lots of organic matter. You can add organic matter by mulching with compost 3 inches deep around the base of your plant. Water will drag the decomposing compost down into the root zone and cycle nutrients and organic matter into your soil. This will also lower the pH slowly over time, which will help your azaleas thrive. If you live in the Midwest and have very neutral or basic soil, you can also fertilize your azaleas and rhododendrons with food