The Best Soil Mix for Azaleas

Gardeners love azaleas for their burst of springtime color and glossy foliage. They thrive in a variety of locations, thriving best in Zones 6 to 8. However, even in an ideal climate, the azalea's cultural requirements must be met. Top on the list of these "must-haves" for azalea success is well-prepared soil.

Azaleas have delicate roots and require soil that is well drained and easily penetrable. Plant azaleas in beds rather than individual holes so that prepared soil is used more efficiently. Avoid putting your azalea bed under the canopy of shallow-rooted trees such as elm, maple or ash. The feeder roots of these trees will quickly grow into the improved soil and compete with your shrubs for water and nutrients.

Azaleas must have acidic soil to thrive. The ideal soil pH for an azalea bed is between 4.5 and 6.0. If you are uncertain about the pH of your soil, obtain a soil testing kit from your local agricultural extension office and collect a sample according to directions. The soil lab will analyze your sample and send back a report detailing the pH of the soil, and offering recommendations for enriching it for optimum fertility. The most common additives used to correct soil pH are limestone and sulfur -- limestone to raise pH and sulfur to lower it.

One of the keys to maintaining loose, well-drained soil is to amend it with organic matter. Depending on how hard or clay-based your soil is initially, add up to 50 percent organic matter to achieve a looser texture. The Azalea Society of America recommends using fine pine bark or rotted leaves for this purpose. You may also use additional topsoil. Avoid "hot" organic materials such as mushroom compost or materials containing fresh cow manure. These additives are too alkaline and will lower the acidity of the soil.