Rhododendron

Fundamental Facts

HARDINESS: Zones 5 to 8
PREFERRED SOIL pH: Acid
PREFERRED SOIL TYPE: Moist, humus-rich, well-drained
PREFERRED LIGHT: Partial to full shade
ATTRIBUTES: Large flowers, leathery leaves; for specimens, foundations, beds
SEASON OF INTEREST: Year-round; blooms late spring to summer
FAVORITES: Choose varieties suited to local conditions by size and flower color
QUIRKS: Leaves temporarily droop and curl as o protective response to cold weather
GOOD NEIGHBORS: Azalea, fern, mountain laurel, hydrangea, mahonia, dogwood, holly
WHERE IT GROWS BEST: Partial shade in moist, organically rich soil
POTENTIAL PROBLEMS: Dieback, lacebug, root rot
PRUNING: Lives for decades; prune only to remove dead or damaged wood
CRITTER RESISTANCE: Good
SOURCE: Nursery plants
DIMENSIONS: 3-10 ft (1-3 m)tall, 4-15 ft (1.2-4.6 m) wide

Rhododendron in the Landscape

Rhododendrons bring beauty to the spring garden.Their thick, leathery, evergreen leaves vary from 3-6 in (7.6-15.2 cm) long and are carried on woody branches that form elegant tiers. In late spring to summer, trusses of large, tubular flowers adorn the stem tips, each set off by a frame of green leaves. Flower colors include purple, red, white, yellow, and pink.

Mass large rhododendrons for a privacy screen or boundary marker and use compact types along paths or in foundation plantings. Site them carefully, so that their brittle limbs won't spread into high-traffic areas. Fill the foreground of the plantings with a shade-loving groundcover, such as ferns or lamium. Rhododendrons also enjoy the company of their fellow woodland plants, including dogwood and mountain laurel.

Selecting Rhododendrons

There are thousands of species and cultivars, ranging in height from 2 ft (0.6 m) to 8-10 ft (2.4-3 m). Most are hardy to Zone 5 or 6. although Ironclad hybrids are hardy to Zone 4. The best way to find a rhododendron is to visit a local nursery, which will have plants that are adapted to your area. You can select from the plants they carry by size and color.

Among smaller types, look for Yako rhododendrons (R. yakushimanum), a Japanese native that forms a rounded plant with felted young leaves. Two good North American species are the Carolina (R. carolinianum) and catawba rhododendrons (R. catawbiense), both of which have purplish flowers.

The 'P.J.M.' hybrid is popular for its lavender-pink blossoms and small leaves that turn burgundy in the fall. Other favorite hybrids are the lavender blue 'Blue Peter', red 'Nova Zembla'. pink 'Scintillation, creamy yellow 'Unique', and white 'Boule de Neige'.

Growing Rhododendron

Select a site with filtered shade, or one with morning sun and afternoon shade. Plants growing in deep shade may grow leggy and flower poorly, while those in sun will show scorched leaves. Protect them from strong wind, which can shred the leaves.

Rhododendrons need loose, moist soil with a pH of 4.5-6.0, so prepare a roomy planting hole amended with acidic leaf mold or peat moss. Plant in spring and set plants high, so that the topmost roots are barely covered with soil. Spread 3 in (7.6 cm) of compost, bark chips, or other organic mulch over the roots. Water only as needed to keep the soil barely moist. Too much water leads to incurable root rot. Occasional problems with die-back, which causes branch tips to blacken and die, are caused by burrowing caterpillars called borers and by fungal disease. Cut back affected stems to healthy wood and dispose of the damaged portions.

If you see yellow splotches on leaf surfaces and insect excrement on leaf undersides, suspect lacebug. Spray plants with insecticidal soap per label and dispose of fallen leaves to remove the insects' nesting places.