Dwarf rhododendron

Dwarf rhododendron: how do you recognise it?

Habit

Dense, cushion-forming dwarf shrub about 50 cm tall and 80 cm wide, with many fine, branching twigs.

Leaves

Evergreen, small and oval, about 1 cm long, grey-green and covered in tiny scales.

Flowers

Small, open funnel-shaped flowers 1–2 cm across, in clusters at the tips of the twigs, in April–May.

Colour

Violet-blue to lilac; there are selections and hybrids in other shades of blue and purple.

Roots

Fine and shallow, forming a mat just below the surface: do not hoe around the plant.

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

Why grow it?

• Stays small and compact without much pruning: ideal for small gardens, rock gardens and containers.
• Evergreen: a dense, grey-green cushion even in winter.
• Abundant flowers in April–May, in an unusual violet-blue.
• Bees and bumblebees visit the early flowers.
• A perfect partner for heathers and other acid-loving plants.

Dwarf rhododendron: where does it grow best?

• Full sun to partial shade. In sun it stays more compact and flowers more, provided the soil stays moist.
• Acid, humus-rich soil (pH about 4.5–5.5): sandy, loamy or peaty. On chalky soil or heavy clay, grow it only in a container with ericaceous compost.
• Evenly moist but well drained: never let it dry out and never let it sit in water.
• Sheltered from cold, drying east winds, which scorch the evergreen leaves.
• Allow 60–80 cm between plants; as a low edging, 50 cm.

Light

Sun and partial shade

Soil type

Sand, loam or peat

Acidity

Acid

Moisture

Normal

Size

0.5 m tall, 0.8 m wide

Hardiness

Hardy (to -25 °C)

Goes well with

• Heather: The same acid soil and full sun; together a colourful heather garden.
• Pieris: Evergreen shrub with white flower trusses in spring, also for acid soil.
• Checkerberry: Low, evergreen ground cover with red berries at its feet.
• Dwarf conifers: Shape and structure all year in a rock garden or container.
• Ferns: Fresh companions in partial shade for the same humus-rich, moist soil.

Dwarf rhododendron: when and how to plant it?

Plant in March–April and September–October.

1. Plant in March–April or September–October.
2. Soak the root ball in a bucket of water until no more air bubbles rise, and gently loosen a pot-bound root ball.
3. Dig a wide, shallow hole and mix the soil with ericaceous compost or leaf mould.
4. Plant high: the top of the root ball should be level with or just above the soil surface, never deeper.
5. Firm in and water with rainwater.
6. Spread a mulch of pine needles, composted bark or leaf mould around the plant.

Care

Watering

Preferably rainwater, as tap water is often hard. Water during dry spells, also in late summer when next year’s flower buds are forming.

Feeding

In March–April a little ericaceous fertiliser or some leaf mould. Not too much and not after June.

Mulching

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

Deadheading

Not necessary with these small flowers; for a tidy look, snip off the faded clusters after flowering.

In a container

Use ericaceous compost and a pot with a drainage hole. Refresh the compost or repot every two to three years.

Tip: Water with rainwater and keep the soil slightly moist at all times, especially in late summer when next year’s flower buds are forming.

Dwarf rhododendron: when to prune it?

Pruning months: June.

When: Hardly needed. To keep it more compact, trim lightly straight after flowering, in June.

How:

• Lightly trim the flowered twigs to keep the cushion dense and rounded.
• Remove dead or frost-damaged twigs.
• Do not cut hard into old, bare wood: it regrows poorly from there.

Caution: Do not prune after July: next year’s flower buds form in late summer.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Semi-ripe cuttings

In July–August take 5–8 cm cuttings from semi-ripe shoots and root them in a mix of ericaceous cutting compost and sand, under plastic. They root slowly: be patient.

Layering

In spring peg a low twig into the soil; after a year sever it and replant.

Seed

In spring scatter the dust-fine seed on moist, acid seed compost without covering it. Seedlings take several years to flower.

Dwarf rhododendron: how does it get through the winter?

Hardy to −25 °C.

• Hardy to about −25 °C: no protection is needed in Belgian gardens.
• The evergreen leaves can dry out in hard frost combined with bright sun and dry wind. Water well in autumn and choose a sheltered spot.
• In a container: stand it against a wall, wrap the pot in hessian and water now and then when it is not freezing.
• During long, severe frosts you can cover the plant temporarily with fleece or conifer branches.

Diseases and pests

• Yellow leaves: Yellow leaves with green veins point to soil or water that is too limy. Water with rainwater, mulch with pine needles and use ericaceous compost.
• Vine weevil: Half-moon notches in the leaf edges; the grubs eat the roots. Apply nematodes against the grubs in spring or late summer.
• Root rot: The plant suddenly wilts in wet, poorly drained soil. Plant higher and improve drainage.
• Drought damage: Brown leaf edges and few flower buds. Water with rainwater in dry weather and keep a mulch in place.

Through the year

• March: Plant. Ericaceous fertiliser and a fresh mulch.
• April: Flowering starts. Plant. Bees on the flowers.
• May: Full flower. Watch for vine weevil damage.
• June: Trim lightly after flowering. Snip off faded clusters.
• July: Take semi-ripe cuttings. Water with rainwater in dry weather.
• August: Next year’s flower buds are forming: do not let it dry out. Nematodes against vine weevil.
• September: Plant.
• October: Plant. Water well before winter.
• December: Protect pots in 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?

• It belongs to the scaly-leaved (lepidote) rhododendrons: the leaves are covered in tiny scales, easy to see with a hand lens.
• In the wild it grows high in the mountains, up to above the tree line. That explains its compact habit and its hardiness.
• Rhododendrons belong to the heather family, like heather, bilberry and pieris: all plants that like acid soil.