Rhododendron Southern Indica Hybrids

Southern indica hybrid azalea is a woody, deciduous shrub in the Ericaceae (blueberry) family.  The genus name derives from the Greek words rhodo, which means rose, and dendron, meaning tree. Hybrid plants are created by cross-pollinating two varieties to achieve certain desirable plant characteristics. This group of hybrid azaleas grows well in the sun and are one of the first azaleas to bloom with very large showy blossoms that cover the shrub.

Like other azaleas, it requires humus-rich, acidic, and moist soil with good drainage. This variety of Rhododendron has numerous cultivars. Many tolerate both full sun and heat, although some may be less tolerant of high heat. This plant is moderately salt tolerant. The cultivars range in size but typically can be 6 to 12 feet high and 6 to 8 feet wide.  It is very tolerant of pruning which should be done after flowering and as the next year's flower buds form in the summer.  

Bloom colors include a wide range from bright yellow to purple, depending on the cultivar. The large blooms attract bees and hummingbirds. Plant in any sunny location as a specimen or in groups, with proper soil conditions and some dappled shade for non-high heat tolerant varieties.  They work well as background shrubs or are used as an attractive flowering hedge.

Insects, Diseases, and Other Plant Problems:  Insect problems include aphids, borers, lace bugs, leafhoppers, mealybugs, mites, nematodes, scale, thrips, and whitefly.  Diseases include canker, crown rot, root rot, leaf spot, rust, and powdery mildew. This plant is frequently damaged by deer.

While these shrubs remain very popular for landscape use, many cultivars are susceptible to Phytophthora root rot—this leads to leaf loss, reduced vigor, branch dieback, and wilting. Implement good cultural practices first, such as improving drainage with organic matter or berms and avoiding overwatering or overfertilization.  However, if you have a site with a history of this disease, consider planting one of the root rot-resistant alternative species.  

For suitable alternatives, see this video created by Charlotte Glen as part of the Plants, Pests, and Pathogens series.

VIDEO Created by Elizabeth Meyer for "Trees, Shrubs and Conifers" a plant identification course offered in partnership with Longwood Gardens.

More information on Rhododendron.