This species is used as a parent in many hybrids, including the Ghent Hybrids, Knapp Hill Hybrids and Ilam Hybrids.
Common Groups of Hybrid Rhododendrons
'Girard' Hybrids: This large group of azaleas includes both deciduous and evergreen cultivars. They vary in flower color and winter hardiness.
'Knapp Hill' Hybrids: The result of crosssing several species of Rhododendron. A large group including 'Knapp Hill', 'Exbury', 'Slocock' and 'Ilam' Hybrids. These azaleas are deciduous. Flower color depends on the cultivar selected. Mildew can be a problem with this group. Hardiness zones 5-7.
'Northern Lights' Hybrids: Developed at University of Minnesota. These hybrids were selected for excellent cold hardiness (to -30 degrees). These azaleas are deciduous. Flower color depends on cultivar selected.
'P.J.M.' Hybrids:A group of hybrids that are known for their compact size (3-6 feet) and their flower color (shades of lavender pink to mauve). These rhododendrons are evergreen, with the foliage taking on a purplish cast in winter. Hardiness zones 5 to 7.
Additional pests and problems that may affect this plant:
Leaf spots, powdery mildew, scale, thrips and whitefly are possible problems, but occur only occasionally.
Alkaline soils will lead to chlorosis (yellowing ) of the leaves.
Rhododendron and azaleas both fall into the genus Rhododendron. For more information on rhododendrons visit the American Rhododendron Society website www.rhododendron.org