Rhododendron family shrubs, azaleas bring spring and occasional fall color to the garden. These showy plants may be deciduous or evergreen. All azalea plant varieties, however, benefit from loose, acidic, pH between 5.0 and 5.5, well-drained soil, according to the Louisiana State University AgCenter Research and Extension. Early spring fertilizer and pine-or-cypress-based mulches also help plants perform their best.
Indian azalea (Rhododendron indicum) is a broadleaf evergreen shrub native to Japan. Usually standing 2 to 3 feet high and wide, this heavily branched plant has clusters of 2-1/2 inch, funnel-like flowers in shades of red. Blooming in late May and June, they contrast well with the plant's glossy, lance-shaped deep green leaves. Autumn foliage is red-tinged.
Like all rhododendron family plants, Indian azalea is vulnerable to a host of pests and diseases. They include crown and root rot, leaf spot, mites, scale and aphids. Although advertised as hardy to 0 degrees F, this azalea benefits from heavy winter mulch and a protected location in the lower end of its hardiness range. Give it sun-dappled, partial shade and well-drained, acidic soil, advises the Missouri Botanical Garden.
Roseshell azalea (Rhododendron prinophyllum) grows wild along streams and on forest north slopes throughout the Eastern United States. Hardy to minus 40 degrees F, this deciduous plant blooms in April and May. Small, up to 1-1/2 inches across, pink blooms appear in clusters simultaneously with or just before the foliage emerges. This azalea has a mild clove fragrance, according to the Missouri Botanical Garden. Its vivid green leaves provide bronze fall color before dropping. A rounded shrub, roseshell azalea stands 4 to 8 feet high. Use it as a specimen or group planting. It performs best in humus-rich, averagely moist well-drained soil and partial shade. This azalea seldom needs pruning.
Evergreen Azalea 'Robleja'
Evergreen azalea (Rhododendron 'Robleja'), also sold as autumn sweetheart, is an encore series hybrid. Standing from 3 to 5 feet high and up to 4 feet side, it tolerates temperatures to 0 degrees F. This densely branched, round shrub has May clusters of purple-spotted, pink flowers. The up-to-2-1/2-inch blooms become white as they age. Like other encore azaleas, robleja may rebloom in late summer or fall. Deep green leaves change to yellow-green in winter.
Use robleja, recommends the Missouri Botanical Garden, in a shrub border, hedge or foundation planting. Provide consistently moist, well-drained soil high in organic material. The plants tolerate morning sun and afternoon shade, handling more sunlight the further north they grow. Protect them from strong winds. Keep them away from juglone-producing plants. Hickory, pecan, butternut and walnut trees all release chemicals toxic to most azaleas.