Yellow azalea

Yellow azalea: how do you recognise it?

Habit

Upright, open shrub 2–2.5 m tall and about 2 m wide, with stiff branches.

Leaves

Oblong, 5–10 cm, slightly hairy and somewhat sticky, fresh green; deciduous.

Flowers

Funnel-shaped, golden-yellow flowers of 4–5 cm, sticky on the outside, with long stamens, in clusters at the shoot tips, in May.

Scent

Heavy, sweet and honey-like, strongest on warm days.

Autumn colour

Fiery orange, red and purple in October.

Roots

Shallow and fine, as in all rhododendrons: sensitive to drought, lime and deep planting.

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

Why grow it?

• One of the most fragrant shrubs in May: its sweet, honeyed scent carries a long way.
• Golden-yellow flowers that light up partial shade.
• Superb autumn colour in orange, red and purple.
• Bees and bumblebees visit the flowers.
• Fully hardy and, on the right acid soil, little work.
• A piece of Flemish garden history: an ancestor of the Ghent azaleas.

Yellow azalea: where does it grow best?

• Sun to partial shade. In sun it flowers best and colours most brightly, as long as the soil stays moist.
• Acid, humus-rich soil: sand, loam or peat. On chalky soil it turns yellow and declines.
• Moderately moist and well-drained: do not let it dry out, but avoid standing water.
• Sheltered from strong, drying winds; the light shade of tall trees is ideal.
• Allow about 2 m per plant.

Light

Sun and partial shade

Soil type

Sand, loam or peat

Acidity

Acid

Moisture

Normal

Size

2.5 m tall, 2 m wide

Hardiness

Hardy (to -25 °C)

Goes well with

• Japanese maple: Fine leaves and equally beautiful autumn colour, in the same sheltered spot.
• Ferns: A fresh green underplanting for the acid, humus-rich soil.
• Evergreen rhododendron: Likes the same soil and gives greenery in winter, when the azalea is bare.
• Hosta: Large leaves at the base in partial shade.
• Bluebell: Blue flowers beneath the shrub in spring.

Yellow azalea: when and how to plant it?

Plant in March–April and September–October.

1. Plant in March–April or September–October, when the soil is moist and not frozen.
2. Dig a wide, shallow hole and mix the soil with leaf mould, bark compost or ericaceous compost.
3. Plant high: the top of the root ball may sit 2–3 cm above the soil. Never plant deeper than it was in the pot.
4. Soak a dry root ball in a bucket of water for a quarter of an hour first, then firm the soil lightly around it.
5. Water in thoroughly straight away, preferably with rainwater.
6. Spread a 5–8 cm layer of bark, pine needles or leaves around the base.

Care

Water

Keep the soil moist, especially in the first year and in July–August, when next year’s flower buds are forming. Use rainwater.

Feeding

In March–April, an organic feed for acid-loving plants. Never lime or limy fertilisers.

Mulching

Top up the layer of bark, pine needles or leaf mould every spring; leave fallen leaves in place in autumn.

Soil

Do not hoe or dig around the shrub: the shallow roots are easily damaged.

Spent flowers

Snap them off carefully after flowering: it looks tidier and the shrub puts its energy into new buds.

Tip: Plant it high in acid, humus-rich soil and keep the mulch thick. Above all, give rainwater in dry spells in July and August: that is when next year’s flower buds are formed.

Yellow azalea: when to prune it?

Pruning months: June.

When: Pruning is hardly needed. If you do prune, do it in June, straight after flowering.

How:

• Snap or cut off the faded flower clusters; take care of the young shoots and buds just below.
• Remove dead, diseased or crossing branches.
• Renew a shrub that is too large or bare by taking out one or two of the oldest stems low down each year.
• Do not prune in winter or early spring: you would remove the flower buds.

Caution: Wear gloves when pruning: all parts of the plant are poisonous.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Layering

The easiest method: in spring, bend a low branch to the ground, lightly wound the bark, peg it down and cover with acid soil. Sever after 1–2 years.

Seed

Sow the fine seed in February–March on the surface of moist ericaceous compost, under glass in a bright spot. Seedlings grow slowly and take several years to flower.

Softwood cuttings

In May–June, cuttings of young shoots under plastic with bottom heat. Tricky, but it can work.

Yellow azalea: how does it get through the winter?

Hardy to −25 °C.

• Fully hardy to about −25 °C: even the flower buds need no protection.
• Leave fallen leaves in place: they protect the shallow roots and keep the soil acid.
• In a dry autumn, water before the frosts set in.
• In a pot: stand it against a wall and wrap the pot in hessian so the root ball does not freeze.

Diseases and pests

• Powdery mildew: White to grey powder on the leaves in summer; deciduous azaleas are prone to it. Choose an airy spot, keep the soil from drying out and clear up affected leaves.
• Yellow leaves (chlorosis): Yellow leaves with green veins: the soil or water is too limy. Water with rainwater, mulch with pine needles and give a feed for acid-loving plants.
• Bud blast: Flower buds turn brown or grey in winter and grow tiny black bristles. Snap them off and put them in the household waste.
• Vine weevil: Half-moon notches in the leaf edges; the grubs feed on the roots. Apply nematodes against the grubs in late summer and pick off the adults by hand in the evening.
• Drought: Drooping leaves and few flower buds. Water regularly with rainwater in summer and keep the mulch thick.

Through the year

• March: Plant. Give a feed for acid-loving plants.
• April: Plant. Top up the bark or leaf mulch. The buds swell.
• May: Flowering: fragrant golden-yellow flowers. Watch for vine weevil.
• June: Snap off faded flower clusters carefully. Prune lightly if needed.
• July: Water in dry spells, preferably with rainwater: next year’s buds are forming.
• August: Water in dry spells. Apply nematodes against vine weevil grubs.
• September: Plant.
• October: Autumn colour in orange, red and purple. Plant.
• November: Leave fallen leaves as mulch.

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?

• Honey from the yellow azalea and related rhododendrons around the Black Sea can be poisonous. The Greek historian Xenophon describes soldiers falling ill in 401 BC after eating such wild honey.
• It is one of the main parents of the Ghent azaleas, bred by nurserymen in the Ghent area in the 19th century.
• The name Pontic refers to Pontus, the ancient name of the region on the southern coast of the Black Sea.