Yakushima rhododendron

Yakushima rhododendron: how do you recognise it?

Habit

Dense, dome-shaped shrub that reaches about 1 m tall and 1.5 m wide after many years.

Leaves

Narrowly elliptic, 7–10 cm, thick and leathery, dark green with rolled edges and a thick brown felt underneath.

Young shoots

Covered in silvery-white hairs, giving the shrub a silver sheen in late spring.

Flowers

Trusses of about ten bell-shaped flowers in May: deep pink buds, pale pink flowers, fading to white.

Roots

Fine, dense and very shallow: they cannot cope with deep planting or digging around the shrub.

Flowering: May · Plants: March–April and September–October · Pruning: June

Why grow it?

• Compact and slow-growing: ideal for a small garden, a rock garden or a large pot.
• Three colours in one show: deep pink buds, pale pink flowers and white as they fade.
• Handsome leaves all year, with silvery-white young shoots and brown felt beneath.
• Tolerates more sun than most rhododendrons.
• Its flowers attract bumblebees and bees in May.

Yakushima rhododendron: where does it grow best?

• Sun or partial shade; in full sun keep the soil cool and moist with a thick mulch.
• Acid, humus-rich soil: sandy, loamy or peaty. On chalky soil it turns yellow and declines.
• Average, slightly moist soil that drains well; it dislikes both waterlogging and drought.
• It copes with wind, but a spot without early morning sun after a frosty night spares the leaves.
• Allow 1.2–1.5 m per plant.

Light

Sun and partial shade

Soil type

Sand, loam or peat

Acidity

Acid

Moisture

Normal

Size

1 m tall, 1.5 m wide

Hardiness

Hardy (to -25 °C)

Goes well with

• Japanese andromeda: An evergreen shrub for the same acid soil, with sprays of white flowers in spring.
• Japanese maple: Fine, graceful foliage and autumn colour beside the compact rhododendron.
• Heather: A low, flowering edge in sun on acid soil.
• Ferns: Fresh, fine foliage for the partial shade around the shrub.

Yakushima rhododendron: when and how to plant it?

Plant in March–April and September–October.

1. Plant in March–April or September–October.
2. Dig a wide, shallow hole and fill it with a mix of garden soil and peat-free ericaceous compost or leaf mould.
3. Plant high: the top of the root ball should sit just above the soil. Never plant deeper than it was in the pot.
4. Keep 1.2–1.5 m from other shrubs.
5. Water in thoroughly with rainwater straight away; plunge a dry root ball in a bucket of water first.
6. Spread a 5 cm layer of pine needles, bark or leaf mould around the base.

Care

Watering

Water generously in dry spells, preferably with rainwater: hard tap water makes the soil less acid over time.

Feeding

In April, a little organic feed for rhododendrons or ericaceous plants. Do not feed after June.

Mulching

A layer of pine needles, bark or leaf mould every spring keeps the soil acid, cool and moist.

Spent trusses

After flowering, carefully snap them off between thumb and forefinger, without damaging the young buds beneath.

Digging

Never dig or hoe around the shrub: the roots lie just below the surface.

In a pot

A wide pot with ericaceous compost and drainage holes. Water with rainwater.

Tip: Plant it high, with the top of the root ball just above the soil, and mulch every year with pine needles or bark. After flowering, carefully snap off the spent trusses without touching the young buds.

Yakushima rhododendron: when to prune it?

Pruning months: June.

When: Hardly ever needed. After flowering, from late May to June, snap off the spent trusses.

How:

• Carefully snap off each spent truss, just above the young shoots or buds.
• Cut out dead or damaged stems back to healthy wood.
• If needed for the shape, shorten a single wayward stem just above a whorl of leaves.

Caution: Do not prune hard: it grows slowly and recovers poorly. Pruning in summer or autumn removes next year’s flower buds.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Layering

In spring, bend a low stem to the ground, lightly wound the bark underneath and peg it down under acid soil. Sever after one to two years.

Semi-ripe cuttings

In August–September, with some bottom heat and under plastic. Slow and not always successful; layering is easier.

Yakushima rhododendron: how does it get through the winter?

Hardy to −25 °C.

• Hardy to about −25 °C: no protection needed in Belgian gardens.
• In hard frost the leaves roll downwards; this is normal, and they unroll again when it thaws.
• Water during a dry, frost-free spell: evergreens can dry out in winter.
• In a pot: stand it against a wall and wrap the pot in hessian or bubble wrap so the roots do not freeze.

Diseases and pests

• Yellow leaves with green veins: Chlorosis caused by chalky soil or tap water. Use rainwater, mulch with pine needles and use an ericaceous feed.
• Vine weevil: Half-moon notches in the leaf edges; the grubs eat the roots. Pick off the beetles at night by torchlight or use nematodes against the grubs.
• Bud blast: In spring, flower buds turn greyish brown with tiny black bristles and do not open. Snap them off and throw them away, not on the compost heap.
• Root rot: Leaves wilt and discolour despite wet soil. Plant high in well-drained soil and make sure water never stands.

Through the year

• March: Plant. Look out for buds with bud blast.
• April: Feed and mulch. The buds turn deep pink.
• May: Flowering: pink flowers that fade to white. Bumblebees and bees.
• June: Snap off spent trusses. Silvery-white young shoots. Last feed.
• July: Water in dry spells, preferably with rainwater.
• August: Water in dry spells. New flower buds are forming.
• September: Plant. Take semi-ripe cuttings.
• October: Plant. Top up the mulch.
• December: Protect pots from hard frost.

Edible and useful

Not edible. Rhododendrons and azaleas are poisonous in all their parts, including the flowers and nectar: they contain grayanotoxins, which cause drooling, vomiting, weakness, a slow heartbeat and low blood pressure. Goats, sheep and alpacas above all, but also horses, cattle, rabbits and guinea pigs become seriously ill from them, sometimes after only a small quantity of leaves; dogs and cats are at risk too. So never throw clippings over the fence of a field or into a pen or hutch, do not give them to animals, and do not pick greens for rabbits among the shrubs; if in doubt, call your vet at once. In children who put a leaf or flower in their mouth or suck nectar from the flowers, as they do with dead-nettle, it usually goes no further than a burning mouth and nausea, but teach them not to do it. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• Yakushima island is a UNESCO World Heritage Site, known for its heavy rainfall and centuries-old Japanese cedars.
• The famous clone ‘Koichiro Wada’ is named after the Japanese nurseryman who sent the plant to England in the 1930s.
• Thanks to its compact growth and handsome leaves, it became one of the most important parents of compact garden rhododendrons.