Fertilize andromeda in either the fall or early spring. Use a timed-release granular fertilizer labeled for acid-loving plants, such as a 4-3-4 analysis.
Rake back the mulch, if any, beneath the andromeda shrub. The annual fertilizer application is also a good time to apply fresh mulch.
Measure the andromeda's branch spread, and use 1 cup of fertilizer per foot. Sprinkle the fertilizer around the drip line --- this is the area of the soil that corresponds to the widest part of the plant.
Rake the fertilizer around the andromeda to lightly mix it in with the top layer of soil.
Water the shrub to a depth of 6 inches to move the fertilizer into the soil.
Replace the mulch on the soil around the andromeda, keeping it 6 inches from the base and spreading it out to the drip line.