Rhododendron arboreum aka Tree Rhododendron

Rhododendron arboreum is an evergreen tree in the heath family, Ericaceae. Kew places its native range from the Himalayas to southern Tibet. It grows in mountain forests and shrubland. Habitat records place it at 4,920–11,810 feet [1,500–3,600 metres]. Its tall, narrow shape suits gardens with room for a tree. The RHS gives a garden height of 26–39 feet [8–12 metres]. Its spread reaches about 8–13 feet [2.5–4 metres]. Plants take 20–50 years to reach their full size.

The leaves stay on the tree throughout the year. They are dark green and reach about eight inches long. A smooth layer of fine hairs coats their undersides. This covering, called indumentum, can be cinnamon brown, fawn, or silver. Rounded flower clusters appear in early spring. Each flower can reach about two inches long. Flowers may be red, white, or shades of pink. Spots often mark the inside of the flower throat. The spring flowers and upright form give it landscape value.

Grow this tree in part shade with shelter. It needs acid soil rich in humus and leaf matter. The soil should stay moist while letting excess water drain. Both sandy soil and loam suit it. A woodland garden with dappled light offers a suitable setting. The RHS also lists cottage and informal gardens as uses. Its UK hardiness rating is H4. This covers winter lows around 14–23°F [-10 to -5°C]. Plants For A Future lists USDA zones 6–9.

Several pests can attack the tree. These include vine weevil, whitefly, leafhoppers, and lacebugs. Scale insects, caterpillars, and aphids may also cause trouble. Diseases include powdery mildew, petal blight, and bud blast. Silver leaf and honey fungus are further risks. Growers can raise plants from ripe seed or late-summer cuttings. Other methods include autumn layering and grafting.

The RHS warns that eating this plant harms people and pets. Plants For A Future calls the leaves poisonous. It also records cooked leaf use and raw or cooked flowers. These food records do not establish safety. Large amounts of flowers can cause intoxication. Traditional remedies use the leaves, bark, and flowers. The wood serves for fuel, charcoal, furniture, and household items. Heavy fuel harvesting has raised conservation concerns.