Azalea and Rhododendron are included in a single genus (Rhododendron) that represents 500 to 900 species of evergreen and deciduous trees and shrubs plus many thousands of cultivated varieties displaying a wide diversity of flower colour, foliage traits, growth habits, and flowering dates. By carefully selecting varieties, it is possible to have Azalea and Rhododendron flowering from late autumn through summer. They are typically used in foundation plantings, as well as specimen plantings in the landscape.
Culture for Azalea and Rhododendron
Azalea and Rhododendron thrive in partial shade, but some varieties will tolerate full sun or dense shade. Flowering is most prolific if plants receive at least partial sun. Protection from strong wind is critical to prevent desiccation and winter injury especially on evergreen varieties. Plants require moist but well drained leafy, humus, rich acid soil acid (pH 4.5 to 5.5). Shallow planting is essential! Rhododendrons are shallow rooting and will not tolerate deep planting. Nutrient deficiencies commonly occur on soils that are alkaline and poorly drained.
Concerns about Azalea and Rhododendron
Susceptible to vine weevil, azalea and rhododendron whiteflies, leafhoppers, scale insects, caterpillars aphids. Scale and borers can infest branches and stems. Phytophthora root rot is the most destructive disease affecting this plant group. Other diseases include powdery mildew, bud blast, honey fungus, rust, leafy gall, petal blight, and silver leaf.
Management Practices for Azalea and Rhododendron
Sample soils for nutrient and pH levels especially if deficiency symptoms were evident during the growing season. Fertilise or amend soil as specified in autumn or spring. Apply fungicide/insecticide/phosphite spray treatments commencing in early spring. Prune out and destroy (burn) shoots with cankers.