Camellia japonica and most of its cultivars are considered to be winter hardy to USDA Zones 7-9. Even where winter hardy, unusually cold temperatures in winter (below 10 degrees F), particularly when occurring as a sudden temperature change, can damage or sometimes kill these plants. Japanese camellias may not be grown outdoors year round in the St. Louis area (USDA Zone 6) except for a very limited number of recently developed cultivars which have displayed exceptional hardiness.
Where winter hardy, Camellia japonica should be grown in moist, acidic (5.5 to 6.5 pH), loose, organically rich, well-drained soils in part shade. Consistent and even moisture is important. Avoid wet soils. Plants require protection from direct afternoon sun and wind. Best location may be sun-dappled part shade. Best with a root mulch. Near the northern parts of their growing range, plants should be sited in sheltered and protected microclimates such as near the south side of a home or building. Burlap wraps are sometimes helpful. Plants generally dislike changes in temperature, irregular watering or being moved. Even a change in humidity can cause plants to drop buds. Fertilize monthly in spring and summer. If desired, remove all but one bud from each cluster to increase the size of the flower. Prune immediately after flowering.
Container plants are an option for the St. Louis area and other places where plants are not winter hardy, but containers are typically not an effective option because camellias generally overwinter poorly in private residences where growing conditions and room temperatures cannot be controlled. For container plants to thrive indoors, they must be overwintered in a temperature-controlled environment such as a greenhouse where maximum winter temperatures range from 45 to 55 degrees F. Flower buds typically fall off where winter temperatures exceed 55 degrees F.
A limited number of cultivars of this species are now temperature rated to USDA Zone 6, and may be grown outdoors all year in the St. Louis area in protected locations around homes, foundations and patios.
‘Korean Fire’ has unusually good winter hardiness (one of the best of the C. japonica cultivars). It is currently recommended for growing outdoors year round in USDA Zone 6. It is likely to survive winter outdoors in the St. Louis area with bloom occurring in April. Notwithstanding winter hardiness ratings, some Japanese camellias recommended for Zone 6 suffered significant damage at the Missouri Botanical Garden Kemper Center as a result of the cold 2013-2014 winter.
Camellia japonica, commonly called Japanese camellia, is an evergreen shrub that typically grows to 6-12’ tall on stems clad with oval, leathery, glossy, dark green leaves (3-4” long) with finely serrated margins. It is native to China and Japan. It is winter hardy to and often grown outdoors year round in the southeastern U.S. plus Pacific coast areas. It is the most commonly grown camellia species comprising thousands of cultivated varieties. It is the state flower of Alabama. The majority of the camellias grown at the Missouri Botanical Garden in St. Louis are grown indoors at the Linnean House. Flower buds begin to form in mid-summer. Buds appear in clusters. Removing all but one bud per cluster will increase flower size. Flowers (3-5” wide) bloom in mid-late winter (December to March) when grown outdoors in warm winter climates or in greenhouses, but bloom in early spring (April) when grown outdoors in the northern part of its growing range. Species plants have single flowers, but cultivars with semidouble, anemone, peony, rose-form double, or formal double flower forms are available. Each single flower has 5-8 petals. Flower colors are most commonly white, pink or red with yellow anthers. Flowers are borne at the tips of shoots or from lower leaf axils. Rounded fruits (1 1/2” long).
Genus name honors Georg Joseph Camel (1661-1706), a German Jesuit missionary to the Philippines who was noted for his work on Oriental plants.
Specific epithet is in reference to native territory of this species.
‘Korean Fire’ is a Japanese camellia introduced by Barry Yinger through Hines Nursery from plants collected in Korea in 1984. It is reportedly capable of surviving winters with sub-zero temperatures (to -10 degrees F) with no injury. This is an evergreen shrub that typically matures, in the absence of injury, to 10-15’ tall and to 8’ wide. Elliptic to obovate, serrate, glossy dark green leaves (to 3” long) are particularly attractive. Fragrant, flat, single red flowers with showy yellow stamens (each flower to 3-5” diameter) bloom in early spring (April). Recipient of the Pennsylvania Horticultural Society Gold Medal Plant Award in 2003.
Camellias are susceptible to a number of fungal diseases including leaf spots, black mold, flower blight, canker and root rot. Scale can be a troublesome insect pest. Aphids, thrips, mealybugs and mites may appear. Yellow leaves may mean too little acidity in the soil. Some flower bud dropping may be natural, but sometimes may be caused by overwatering or underwatering. Limit pruning to removal of dead or damaged wood, unproductive branches, and disproportionately long shoots. Shearing spoils the naturally attractive shape of the camellia. Prune immediately after flowering or in early summer to stimulate branching. Pruning later in the year can remove flower buds.
Excellent flowering shrub for lawns, shrub borders, backgrounds, informal hedges and around homes in mild winter locations. When grown outside their specified hardiness range, camellias are used primarily as conservatory plants, and they perform quite well in this environment. Since they react badly to change (e.g., drop their buds), it is usually not recommended that they be moved outside in the summer months and then returned inside in the fall. If possible, camellias should be grown in a brightly lit space that can accommodate their large spreading habit and be kept cool in the fall and winter to induce flowering.