Rosebay Rhododendron

Size, growth and what to expect

Expect about a foot of new height a year from a young rosebay rhododendron on an average site, the figure our growth estimator uses for a slow grower. In a garden it stands 10 to 15 feet and spreads 5 to 12 feet, while wild thickets in the southern mountains run 10 to 23 feet tall. The oldest stem dated by its rings was 120 years old.

Trusses of pink to white flowers about 2 inches across open from late May in the south to August in the north, and only twigs in full sunlight flower. Each capsule holds about 400 seeds, and a single stem can live 100 years. Deer browse it in fall and winter, grouse and turkeys eat the buds, and the thickets shelter deer, bears and rabbits through the winter. Great laurel is its other common name, and the genus name means rose tree in Greek. The capsules ripen in September and October and shed their seed in November.

It grows wild from Nova Scotia and Ontario south to Georgia and Alabama, most commonly in the eastern mountains, from sea level to 6,000 feet.

How to grow Rosebay Rhododendron

Rosebay rhododendron needs shade, shelter and acid soil. Put it under trees or on the north side of a building, out of winter wind and afternoon sun, in ground that stays moist but drains; it rots in stagnant mud. Space plants 8 feet apart and 6 feet off a foundation.

Saplings ship potted. Plant while dormant, in early spring or fall. Set the root ball in a hole three times as wide and slightly shallower, with the root mass a touch above grade, and use native soil only. If your soil is neutral or limey, choose another plant rather than amending. Mulch with pine needles, kept off the stems. Seed is dust-fine and needs light as soon as it is wet. Sow it on the surface of moist peat mix in winter, uncovered, at room temperature under lights and a clear cover. Seedlings come up in about three weeks.

The shallow roots dry out fast, so water weekly through the first two summers. Deer browse it in fall and winter, and rabbits eat the bark and buds, so cage young plants where either is common. Voles tunnel under deep mulch, so keep it to two inches. Prune only to remove dead wood.

Rosebay rhododendron carries both male and female parts in each flower, and bees carry the pollen. A lone shrub can set seed with its own pollen, but a second shrub from a different parent sets more. Growth is slow and the plant is long-lived. Leaves that curl and droop on cold mornings are normal. Yellow leaves with green veins mean the soil is not acid enough. Never dig around the roots. Every part of the plant is toxic if eaten.