Rhododendron maximum

Common Name: rosebay rhododendron 
Type: Broadleaf evergreen
Family: Ericaceae
Native Range: Eastern North America
Zone: 3 to 7
Height: 5.00 to 15.00 feet
Spread: 5.00 to 12.00 feet
Bloom Time: June to July
Bloom Description: Rose-purplish to pink to white
Sun: Part shade to full shade
Water: Medium
Maintenance: Medium
Flower: Showy
Leaf: Evergreen
Other: Winter Interest
Tolerate: Rabbit, Heavy Shade

Culture

Winter hardy to USDA Zones 3-7 where it is best grown in acidic, humusy, organically rich, cool, moist, moisture-retentive but well-drained soils in part shade. Tolerates close to full shade. Avoid hot summer locations. Roots must never be allowed to dry out. Acidify soils prior to planting and thereafter as needed. Plant in a location protected from strong winter winds. Good soil drainage is essential (doesn’t like “wet feet”). Poor drainage inevitably leads to root rot, therefore raised beds/plantings should be considered in areas with heavy clay soils. Shallow, fibrous root systems (do not cultivate around plants) will benefit greatly from a mulch (e.g., wood chips, bark or pine needles) to help retain moisture and stabilize soil temperatures. All parts of this plant are highly toxic if ingested.

Noteworthy Characteristics

Rhododendron maximum, commonly called rosebay rhododendron or great laurel, is a large, upright, loose, multi-stemmed, late-blooming, evergreen shrub that is native to North America from Ontario and Nova Scotia south to Ohio, Alabama and Georgia with a concentration of plants in the southern Appalachian Mountains where it typically grows in dense thickets which dominate the understory in some locations. It typically grows to 5-15’ tall, but infrequently to 30-40’ tall in the heart of its native habitat. Large, leathery, strap-like, evergreen leaves (typically to 4-8” long) have undersides with a hint of rusty orange. Flowers (to 2” across) are rose-purplish to pink to white, often with olive green to orange spots. Flowers bloom in umbel-like inflorescences from June to early July. Fruit is an oblong seed capsule which splits open when ripe to release numerous seed.

Genus name comes from the Greek words rhodo meaning rose and dendron meaning tree. Transferred from the Greek name for Nerium oleander.

Specific epithet means largest.

Problems

Rhododendrons are susceptible to many insect and disease problems, including but not limited to canker, crown rot, root rot, leaf spot, rust, powdery mildew, aphids, borers, lacebugs, leafhoppers, mealybugs, mites, nematodes, scale, thrips and whitefly. A healthy plant in the proper environment should have limited problems.

Garden Uses

Shrub borders. Shady locations. Naturalistic areas. Wood margins.