Rhododendron yakushimanum, yakushima rhododendron
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Broadleaf Evergreen Shrubs

Rhododendron yakushimanum

yakushima rhododendron

EricaceaeYakushima Island, southern Japan

At a Glance

TypeShrub
HabitMounding
FoliageEvergreen
Height3-4 feet (90-120 cm)
Width4-5 feet (120-150 cm)
Maturity15 years

Growing Zones

USDA Hardiness Zones

5 - 8
Zone 5
Zone 6
Zone 7
Zone 8
These zones indicate the coldest temperatures this plant can typically survive.
Frost Tolerancehardy

Key Features

Attracts Pollinators
Attracts Butterflies
Container Friendly
Maintenancelow

Overview

A compact, dome-shaped evergreen shrub reaching 3-4 feet (90-120 cm) tall with a spread of 4-5 feet (120-150 cm) at maturity. Leaves are oblong-elliptic, 2.5-5 inches (6-13 cm) long and 1-1.5 inches (2.5-4 cm) wide, dark green and recurved above, with a dense, thick indumentum (woolly coating) on the undersides that is initially white, aging to tawny or cinnamon-brown. New growth emerges with a silvery-white tomentose covering that is shed as leaves mature. Flowers are bell-shaped, 1.5-2 inches (4-5 cm) across, opening from deep rose-pink buds to pale pink and fading to white, borne in rounded trusses of 8-12 flowers. This color progression produces trusses with multiple shades simultaneously. Bloom occurs in mid to late spring. Growth rate is slow, adding 1-3 inches (2.5-8 cm) per year; plants require 10-15 years to approach mature dimensions. Branching is dense, forming a symmetrical dome without pruning. Root system is shallow and fibrous. More heat-tolerant than many rhododendron species, performing adequately into zone 8 where summers are not excessively hot and humid. Foliage may develop leaf spot in regions with prolonged summer humidity.

Native Range

Endemic to Yakushima Island in southern Japan, where it occurs at elevations above 5,000 feet (1,500 m) in exposed, wind-swept habitats. Found on rocky outcrops and ridgetops in montane cloud forest zones, adapted to high rainfall, cool temperatures, and acidic substrates.

Suggested Uses

Commonly planted in woodland borders, foundation plantings, and as specimen plants at 4-5 foot (120-150 cm) spacing. Grows in containers of at least 7 gallons (26 L) with acidic potting mix. Widely used as a parent in breeding programs; many compact hybrids in commerce derive from this species.

How to Identify

Distinguished by the thick indumentum on leaf undersides, ranging from white to cinnamon-brown, that persists throughout the leaf's life. Leaves are oblong-elliptic with recurved margins, 2.5-5 inches (6-13 cm) long. New growth covered in silvery-white tomentum. Flowers transition from deep rose-pink buds through pale pink to white, producing multicolored trusses. Compact dome shape is characteristic even on young plants.

Appearance

Size & Dimensions

Height3' - 4'
Width/Spread4' - 5'

Reaches mature size in approximately 15 years

Colors

Flower Colors

pink
white

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~4 weeks
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Spring
Mid-May through early June in zones 5-7; late April through May in zones 7-8. Individual flowers last 10-14 days. Total bloom period extends 3-4 weeks. The color progression from pink buds to white open flowers extends the visual interest of each truss beyond the typical single-color bloom.

Detailed Descriptions

Flower Description

Deep rose-pink buds fading to pale pink then white

Foliage Description

Dark green above with thick white to cinnamon-brown indumentum below; new growth silvery-white

Growing Conditions

Sun Requirements

Partial Shade
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

Soil Requirements

pH Range4.5 - 6.0(Acidic)
357912
Soil Types
loamsandpeat
Drainage
well drained

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

10-15 years

Care & Maintenance

Care Guide

Requires acidic soil with pH 4.5-6.0; amend alkaline soils with sulfur or iron sulfate before planting. Water consistently during the first two growing seasons, providing 1 inch (2.5 cm) per week in the absence of rainfall. Established plants tolerate brief dry spells but leaf margins curl inward as a drought stress indicator; irrigate when curling is observed. Maintain 2-3 inches (5-8 cm) of acidic mulch. More sun-tolerant than many rhododendrons; accepts morning sun with afternoon shade or dappled light throughout the day. Phytophthora root rot and Botryosphaeria dieback are the most significant disease threats in poorly drained or stressed conditions.

Pruning

Rarely requires pruning due to naturally symmetrical dome shape. Remove dead or damaged branches at any time. Spent flower trusses can be removed by snapping at the base after bloom to redirect energy from seed production. Hard pruning is possible but unnecessary on this compact species; if attempted, cut to just above a leaf whorl in late spring.

Pruning Schedule

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late spring

Maintenance Level

low

Container Growing

✓ Suitable for container growing

Minimum container size: 7 gallons

⚠️ Toxicity Warning

Toxic to pets and humans