Yakushima rhododendron

Sun

Partial shade, ideally morning sun and afternoon shade. Tolerates more sun in cool climates if the roots stay moist; protect from hot afternoon sun and drying winds.

Water

Keep the shallow root zone evenly moist but never waterlogged. Water deeply during dry spells, including winter dry spells when the ground is not frozen.

Soil

Acidic, humus-rich, well-drained soil, ideally pH 4.5-6.0. Unsuitable for chalky soil; use a container with ericaceous potting mix where the ground is alkaline.

Height

3-5 ft (0.9-1.5 m), eventually taller in favourable conditions

Spread

4-6 ft (1.2-1.8 m)

Flowers

Late spring to early summer; rounded clusters of pink buds open pale pink and usually fade to white.

Foliage

Evergreen, leathery, dark green leaves with slightly rolled edges and thick cream-to-cinnamon felt beneath. New leaves emerge with a silvery coating that gradually wears away.

Growth

Slow

Care needed

Medium

• Pollinators
• Wildlife
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Moderate

Toughness

Fairly tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   1.6 ft (0.5 m)

2. After 1 year

   1.9 ft (0.59 m)

3. After 2 years

   2.2 ft (0.68 m)

4. After 3 years

   2.5 ft (0.76 m)

5. After 5 years

   3 ft (0.94 m)

About 8 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Toxic

Growth rate

Slow

• Plant with the top of the root ball level with, or slightly above, the surrounding soil; never bury the stem base.
• Water during dry weather, using rainwater where tap water is very alkaline.
• Apply 2-3 in (5-8 cm) of leaf mould or fine pine bark over the root zone, keeping it clear of the stems.
• If growth is weak, apply a light dose of fertiliser for acid-loving shrubs in spring; avoid heavy or late-season feeding.
• Avoid digging or hoeing beneath the shrub because its roots lie close to the surface.

Pruning. Little pruning is needed. Immediately after flowering, remove dead or damaged growth and shorten stray shoots lightly; avoid routine shearing, which spoils the natural shape and removes future flowers.

Late winter

Check for wind damage and water during dry, frost-free periods if the root zone is dry.

Early spring

Refresh the mulch and feed lightly only if growth or soil conditions warrant it.

Late spring

Enjoy the flowers; after they fade, remove spent clusters carefully if practical, without damaging the new shoots below.

Early summer

Complete any light shaping immediately after flowering.

Summer

Check soil moisture regularly and water deeply during dry spells, when next year's flower buds are developing.

Autumn

Plant or transplant in mild climates while the soil is moist and workable; in very cold regions, wait until spring.

• Place at the front of a woodland shrub border, with ferns and hostas beneath taller trees that do not create dense, dry root competition.
• Use as a rounded evergreen anchor beside a shaded entrance or path, leaving room for its mature spread.
• Group with other compact rhododendrons and Japanese pieris for a layered spring display in acidic soil.
• Grow in a broad container with good drainage where garden soil is alkaline, positioning it away from reflected heat.

Garden styles it suits: Woodland, Japanese, English country, Pacific Northwest woodland, Pastel border and Small-space.

Plant it with: Japanese pieris, Japanese maple, Hostas, Japanese painted fern, Barrenwort and Hardy cyclamen.

Wildlife: Flowers attract bumblebees and other visiting insects. The dense evergreen branches provide shelter for small birds.

• Vine weevil: adults notch leaf edges and larvae damage roots, especially in containers. Inspect pots and use an appropriate biological nematode treatment when soil temperatures suit the product.
• Phytophthora root rot: wilting despite wet soil and dying roots often follow poor drainage. Improve drainage before planting, avoid overwatering, and remove badly affected plants.
• Iron chlorosis: yellow leaves with greener veins often indicate alkaline soil or water. Check soil pH, use rainwater, and move the plant to an ericaceous container if necessary.
• Leaf scorch or winter burn: brown leaf edges can follow drought, strong sun or drying winds. Keep roots moist, maintain mulch and provide shelter or afternoon shade.

Toxic to people, cats, dogs and horses if eaten. All parts, including leaves and flowers, contain grayanotoxins; ingestion can cause vomiting, weakness, abnormal heart rhythms and potentially fatal poisoning. Seek urgent medical or veterinary advice after ingestion.

• Catawba rhododendron (Rhododendron catawbiense)

  Usually grows much larger and bears lilac-purple flowers. Its leaf undersides lack the thick felt characteristic of Yakushima rhododendron.

• Rosebay rhododendron (Rhododendron maximum)

  Becomes a much larger shrub, usually flowers later in summer, and lacks the dense cinnamon-coloured felt beneath mature leaves.

The epithet yakushimanum refers to Yakushima, the Japanese island where the plant occurs naturally.

Propagation. Raise the species from seed sown on the surface of acidic seed compost, although seedlings take several years to flower and garden-collected seed may be hybrid. Layering low branches is a practical way to reproduce a particular plant; semi-ripe cuttings need controlled humidity and can be slow to root.

Accepted botanical name

Rhododendron yakushimanum

Native range

Japan.

Sources: GBIF (CC BY 4.0) and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.