Rhododendron, Genus, kaempferi, Species,
- Genus & species
Kaempfer azalea
Overview
Rhododendron kaempferi is a semi-evergreen shrub in the heath family (Ericaceae), 4–10 feet (1.2–3 m) tall and 4–8 feet (1.2–2.4 m) wide, with an upright, twiggy habit. Young stems are covered in brown bristles. Leaves are alternate, elliptic, 1.5–3 inches (4–8 cm) long, and medium green with hairs on both surfaces; larger spring leaves drop in cold winters, and smaller summer leaves persist through winter in zones 7–8. Flowers are funnel-shaped, 1.5–2.5 inches (4–6 cm) wide, orange-red, salmon, red, or rose, with darker spots on the upper lobe, borne 2–4 per cluster in April and May. Fruits are hairy capsules 0.5 inch (13 mm) long. Growth is 6–12 inches (15–30 cm) per year. Roots are shallow and fibrous, and plants decline in alkaline soil above pH 6.5, with yellowing between leaf veins. All parts contain grayanotoxins, which cause vomiting and heart rhythm disturbances in pets and humans if eaten.
Native Range
Rhododendron kaempferi is native to Japan, including Honshu, Shikoku, and Kyushu. It grows on sunny mountain slopes, in open woodland, and in grassland at low to mid elevations.Suggested Uses
Used in woodland gardens, foundation plantings, and mass plantings, spaced 4–6 feet (1.2–1.8 m) apart. Plants are also grown in containers of 5 gallons (19 L) or more with acidic potting mix.How to Identify
Appearance
Size & Dimensions
Height4' - 10'
Width/Spread4' - 8'
Bloom Information
Flowers open in April and May, 2–4 per cluster, with each cluster blooming for 1–2 weeks. Plants flower for about 3 weeks overall. Flower buds are damaged by freezes below 10°F (−12°C) after they swell in early spring.
Detailed Descriptions
Flower Description
Orange-red, salmon, red, or rose with darker spots on the upper lobeFoliage Description
Medium greenGrowing Conditions
Sun Requirements
Requires 3-6 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Grows in part shade to full sun in moist, acidic, humus-rich, well-drained loam with a pH of 4.5–6.0. Hardy in USDA zones 5–8. Plants receive 1 inch (25 mm) of water per week, and shallow roots dry out within days in summer. A mulch layer 2–3 inches (5–8 cm) deep keeps roots cool. Lace bugs, spider mites, and petal blight affect plants, and root rot from Phytophthora develops in wet, poorly drained soil.Pruning
Pruning is done immediately after flowering in May or June, because flower buds form on the previous season's growth by late summer. Stems are shortened by one-third to maintain a rounded shape, and dead wood is removed at the base. Plants regrow from cuts to 12 inches (30 cm) above the soil within one season.Pruning Schedule
Prune: May–June
late spring
Container Growing
Suitable for container growing
Minimum container size: 5 gallons
