Rhododendrons are ornamental, ericaceous, broad-leaved evergreens. Azaleas belong to this genus, but many are not evergreen. They grow best in shade or partial shade. A south or southwest exposure increases the chance of winter injury to evergreen types. Plant in an acid, moist, well drained soil with a pH between 4.5 and 6.5. Several species of azalea and rhododendron are hardy in Michigan. The height and spread depends on the type selected, but some are quite large. Transplanting balled and burlapped or potted plants is most successful. The shallow root systems are easily injured by deep cultivation but benefit from mulching. Remove the old flower clusters as the flowers fade. Plants fail to absorb iron and have yellow leaves with green veins if the soil is not sufficiently acid. Prevent winter burn by avoiding exposed planting sites and by shading during winter.
Some major types of rhododendron and azalea are listed below.
Rhododencron Exbury Hybrids Also called Knap Hill hybrids. These are deciduous shrubs that produce clusters of 2 to 3 inch flowers of various colors.
Rhododendron catawbiense - Catawba Rhododendron Evergreen shrubs reaching a height and spread of 6 feet. Various cultivars produce flowers of white, pink, red, or purple.
Rhododendron P.J.M. A smallish shrubs with a height and spread of 4 feet. It produces a dependable and profuse display of lavendar flowers in very early spring. The dark green foliage turns plum-purple in fall.
Rhododendron x kosteranum - Mollis Azalea Deciduous shrubs reaching a height and spread of 4 feet. These fairly open plants produce flowers of orange, yellow, pink, or white depending on cultivar.