Thunberg spiraea

Thunberg spiraea: how do you recognise it?

Habit

Dense, rounded shrub 1–1.5 m tall and as wide, with thin, gracefully arching branches.

Leaves

Narrowly lance-shaped, 2–4 cm long, finely toothed and light green; yellow to orange in autumn.

Flower

Tiny saucer-shaped flowers less than a centimetre across, in clusters of 2–5 along the branches, in March–April.

Colour

Pure white; pink in bud in ‘Fujino Pink’.

Roots

Finely branched and fairly shallow; easy to move while the shrub is young.

Flowering: March–April · Plants: March–April and October–November · Pruning: April–May

Why grow it?

• One of the first shrubs to flower, as early as March: a white cloud in a still bare garden.
• Early nectar and pollen for bees and bumblebees.
• Fine, willow-like leaves that appear early and turn a lovely orange in autumn.
• Very hardy, unfussy and easy to look after.
• Attractive as an informal hedge, in a mixed border or as a focal point among spring bulbs.

Thunberg spiraea: where does it grow best?

• Sun or partial shade; in full sun it flowers most freely and the autumn colour is best.
• Any good garden soil: sand, loam or clay, acid to chalky.
• Moderately moist; on dry sandy soil give some water in dry summers.
• Allow 1–1.5 m per plant, or 50–60 cm for an informal hedge.

Light

Sun and partial shade

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Normal

Size

1.5 m tall, 1.5 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Grape hyacinth: A blue carpet at the base, in flower at the same time.
• Daffodil: Yellow trumpets beside the white cloud, in March–April.
• Hellebore: Flowers in late winter and spring, lovely at the base in partial shade.
• Forget-me-not: Soft blue flowers beneath the white branches.
• Forsythia: Yellow and white together make a cheerful spring picture.

Thunberg spiraea: when and how to plant it?

Plant in March–April and October–November.

1. Plant in March–April or October–November, when the soil is neither frozen nor waterlogged.
2. Dig a hole twice as wide as the root ball and mix in some compost.
3. Set the plant at the same depth as it was in the pot and firm the soil well.
4. Leave 1–1.5 m between plants, or 50–60 cm for a hedge.
5. Water thoroughly straight away, even if it is raining.
6. Spread a mulch of compost or wood chips around the base.

Care

Water

Every week in dry weather in the first year. After that only in long dry spells.

Feeding

In March, a spadeful of compost or some organic fertiliser for flowering shrubs.

Mulching

A layer of compost or leaf mould in spring keeps the soil moist.

Thinning

Removing a third of the oldest stems after flowering each year keeps the shrub young and free-flowering.

Renovation

An old, leggy shrub can be cut right back to 20–30 cm after flowering; it usually regrows well.

Tip: After flowering, keep the long young shoots and remove only old wood: the shrub will be covered in flowers again every spring.

Thunberg spiraea: when to prune it?

Pruning months: April–May.

When: Straight after flowering, from late April into May. It flowers on last year’s shoots.

How:

• Cut flowered shoots back to just above a strong young shoot.
• Each year remove a third of the oldest, thickest stems at the base.
• Leave the long young shoots: they will carry next spring’s flowers.
• A neglected shrub can be cut right back to 20–30 cm above the ground after flowering.

Caution: Do not prune in winter or early spring: you would cut off all the flower buds.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Softwood cuttings

In June–July take 10 cm cuttings from young shoots, remove the lower leaves and insert them in moist cutting compost under plastic. They root within a few weeks.

Hardwood cuttings

In November–December push 20 cm lengths of ripe one-year-old wood two thirds into the ground in a sheltered spot. Transplant after a year.

Layering

In summer, peg a low branch down into the soil; sever and replant it after a year.

Thunberg spiraea: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: in Belgium it needs no protection.
• A late night frost can brown open flowers; the shrub itself is not harmed.
• In a pot: stand it against a wall and wrap the pot in hessian or bubble wrap in severe frost.

Diseases and pests

• Aphids: On young shoots in spring. Ladybirds and tits usually deal with them; otherwise hose them off with water.
• Powdery mildew: White powder on the leaves in summer, especially in dry weather. Water at the base and keep the shrub open.
• Bare, woody shrub: Few flowers and lots of dead wood at the base. Thin out old stems after flowering every year or cut the shrub right back.
• Poor flowering: Usually pruned too late or too much shade. Prune only straight after flowering.

Through the year

• March: Flowering begins. Give compost. Plant.
• April: Full flower. Plant. Prune after flowering.
• May: Finish pruning. Apply mulch.
• June: Take softwood cuttings. Watch for aphids.
• July: Water in prolonged drought.
• October: Orange autumn colour. Plant.
• November: Plant. Take hardwood cuttings.
• December: Take hardwood cuttings. Rest.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• The species name honours the Swedish botanist Carl Peter Thunberg, a pupil of Linnaeus, who collected plants in Japan in the 1770s.
• In Japan it is called yukiyanagi, meaning ‘snow willow’, after its willow-like leaves and snow-white flowers.
• The name Spiraea comes from the Greek speira, meaning wreath or garland.