Azalea Soil Requirements

Azalea Root Characteristics

• Azalea shrubs develop shallow, fiber-like roots. Spreading generally through the top 6 inches of topsoil, azalea roots are exposed to fluctuating soil temperatures, moisture and availability of nutrients. Native to woodland habitats, azaleas and their hybrid cultivars prosper when the topsoil remains evenly cool and moist and constantly fed by the nutrients leaching from slowly decomposing forest leaf litter. Their roots falter in mucky conditions as well as in compacted, dense ground.

Basic Soil Requirements

• First and foremost, azaleas need to grow in acidic soil conditions. The American Azalea Society lists a pH range of 5.5 to 6 as best, while the University of Missouri recommends slightly lower pH around 5 to 5.5. Overall, a pH between 4 and 6 suffices in the majority of landscapes. A crumbly soil with good texture ensures water drains well so the tiny roots do not suffocate and rot. Any evenly moist soil also sustains azalea shrub health. Dry, sandy soils and dry, compacted clay soils are both unsatisfactory.

Improving Soil

• If the natural soil in the garden drains water poorly, plant azaleas in a raised bed to ensure shrub roots do not sit in standing water any time of year. Adding acid-forming organic matter improves the quality of all soils, including porous, fast-draining sand as well as dense clay. The University of Missouri suggests amending clay soils with a mixture of 50 percent pine bark nuggets, 25 percent grit and 25 percent native soil. By contrast, in sandy soil, mix 50 percent organic matter with 50 percent native sandy topsoil. Incorporate all soil mixtures to a depth of 12 to 16 inches before planting azaleas.

Maintaining Good Soil

• Supplement natural rainfall with irrigation to maintain an evenly moist soil year-round when the soil isn't frozen. An infrequent, deep watering proves better than light, shallow watering since the former encourages deeper root growth. Placing a 2- to 4-inch layer of organic mulch, such as pine bark, oak leaf mold or evergreen needles, provides many benefits. It conserves soil moisture, reduces weeds and helps moderate soil temperatures during both winter cold and summer heat. The aforementioned mulch materials decompose to maintain an acidic pH and provide trace nutrients to sustain healthy growth and flowering.