Azaleas have somewhat low nutritional requirements compared to other shrubs when grown in acidic soil -Do you know the approximate ph of your soil as a starting point for making modifications?

There are several reasons for leaf drop in azalea - they can be sparse and leggy in too much shade, thrips can cause leaf loss as can drought, so fertilizer isn't always the right approach to the problem. I haven't had reason to fertilize my own in my naturally acidic soil, but Holly-Tone is the product often recommended for azaleas and rhododendrons in areas with less than perfect ph, it's 4-6-4 and contains the sulfur, rarely are larger amounts of nitrogen recommended.

Be careful too if you are thinking of cultivating around those surface feeding roots, it's easy to damage them. I find a top dressing of compost the best way to condition soil, slowly feed azaleas, conserve moisture.

After finding out if your ph is too high, call cooperative extension in your state for soil testing, try lowering it with magnesium-organic or ammonium sulfate-inorganic. Don't go to a big box store to look for either one or you will get a huh?, go to a reputable garden center.

Here is a link that might be useful: Propagating Perennials