All azaleas are members of the genus Rhododendron. The Christina azalea is a hybrid variety developed by the Vuyk Van Nes Nursery in the Netherlands and introduced in 1966. Growing to be about 4 feet tall and almost equally wide, Christina is an evergreen azalea, with leaves that redden in the fall but remain on the plant. The flowers are rose pink and double in form. This doubled form is sometimes referred to using an old-fashioned term--"hose in hose"--which means that one set of petals is enclosed by another set.
Christina' is descended from one of the 800 species of rhododendron, Rhododendron kaempferi, the most common azalea species in its native Japan. The Kaempferi species has been widely used in hybridizing and is a parent of Gable, Kaempferi and Kurume hybrid azaleas. Rhododendron kaempferi is a deciduous or semi-evergreen shrub that can grow to 8 feet. The specie's large flowers range from pink to red and orange red.
Development of the Kaempferi Hybrids
Beginning in the late 19th century, Koster's Nursery, of the Netherlands, began work on the Kaempferi hybrids. In 1921, P.M. Koster came to the United States and resumed work ion Kaempferi hybrids in Bridgetown, New Jersey. Hybrization of the kaempferi species also continued in the Netherlands at the C.B. Van Nes and Sons Nursery and the Vuyk Van Nes Nursery, both located in Boskoop. Christina was developed at the latter facility and is sometimes referred to as a Vuykiana hybrid.
Chistina was the result of a cross between two azalea varieties, Florida and Louise Gable.The latter is a salmon-pink, semi-double flowered azalea bred by an American, Joseph Gable of Stewartstown, Pennsylvania. Gable, who was active during the first half of the 20th century, produced many evergreen azalea hybrids, including Louise Gable, a cross between Rhododendron kaempferi and Rhododendron yedoense, a Korean species.
According to the University of Missouri's Growing Guide for Rhododendrons and Azaleas, one of the goals in creating the Gable hybrid azaleas was cold tolerance. Both the parents of Louise Gable, a parent of Christina, are cold tolerant to USDA Zone 6. Christina shares the cold tolerance of its parent and can take temperatures as low as minus 25 degrees Celsius or minus 13 degrees Fahrenheit, making it suitable in climates as cold as USDA zone 5b.
Azaleas, like other members of the Rhododendron genus, do best in soil that is on the acid end of the pH scale--5.0 to 5.5. The plants flourish in well-drained soil with protection from harsh winds. If the soil is very heavy, planting the azaleas in raised beds will provide better drainage. Install in a location where the shrubs will receive very light shade--under trees with high canopies, for example. Because azaleas are water lovers, mulch the area surrounding the plant to conserve moisture.