Nippon spiraea

Nippon spiraea: how do you recognise it?

Habit

Rounded, dense shrub about 1.5 m tall and wide, with long, arching stems.

Leaves

Small, round to oval, 1–3 cm, dark green to bluish green, paler beneath; deciduous.

Flowers

Dense, domed clusters of small white flowers along the upper side of the stems, in June.

Fruit

Small, dry fruits with no ornamental value; they go when you prune after flowering.

Roots

Fibrous and fairly shallow; young shrubs transplant easily.

Flowering: June · Plants: March–April and October–November · Pruning: July

Why grow it?

• A spectacular white display in June, when the spring-flowering shrubs are over.
• An elegant, arching habit, even out of flower.
• Bees and other insects visit the many small flowers.
• Very hardy and easy on almost any soil, including chalk.
• Suits a specimen spot, a mixed border or an informal flowering hedge.

Nippon spiraea: where does it grow best?

• Full sun to partial shade; it flowers most freely in sun.
• Sandy, loamy or clay soil, from acid to chalky.
• Ordinary, well-drained soil that does not dry out for long or stay wet.
• Give it room to arch: allow 1.2–1.5 m per plant, or 70–80 cm apart in a 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

• Hardy geranium: A blue or pink ground cover under the arching stems.
• Catmint: Lavender-blue flowers at its feet that carry on after the spiraea has finished.
• Bluebeard: Blue flowers in late summer that extend the season.
• Ornamental grasses: Airy plumes in autumn, contrasting with the fine leaves.
• Roses: They flower at the same time in June; the white of the spiraea makes pink and red roses glow.

Nippon 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 too wet.
2. Dig a hole twice as wide as the root ball and mix some compost into the soil.
3. Set the shrub at the same depth as it was in its pot; with bare-root plants, spread the roots out neatly.
4. Firm the soil well and water in thoroughly.
5. Spread a mulch around the base and water during dry spells in the first year.

Care

Watering

Regularly in dry weather in the first year; after that only in long dry spells.

Feeding

A little compost or organic fertiliser in March.

Mulching

A layer of compost or wood chips keeps the soil moist and weed-free.

Faded flowers

The dried clusters turn brown; they disappear when you prune after flowering.

Tip: After flowering, cut a third of the oldest stems out at the base and keep the young, arching stems: they will give the best display next year.

Nippon spiraea: when to prune it?

Pruning months: July.

When: Straight after flowering, from late June into July. It flowers on last year’s wood.

How:

• Cut out about a third of the oldest stems right at the base.
• Shorten flowered stems to a strong young side shoot.
• Remove dead and weak stems from the centre of the shrub.
• Never shear it into a ball: that destroys the lovely arching shape.

Caution: Do not prune in winter or spring: you would remove the flower buds and lose the display.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Softwood cuttings

In June–July take 8–10 cm cuttings from non-flowering shoots and root them in moist compost under plastic. They root easily.

Hardwood cuttings

In winter push 20 cm lengths of ripe wood two-thirds deep into the soil in a sheltered spot.

Layering

In spring peg a low stem into the soil and sever it after a year.

Nippon spiraea: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy to about −30 °C: no protection is needed in Belgium.
• It is bare in winter, but the fine, arching stems still give structure.
• In a large pot or container: make sure it drains well and raise the pot on feet.

Diseases and pests

• Aphids: On young shoots in spring. Natural predators usually deal with them; otherwise spray them off with water.
• Powdery mildew: White powder on the leaves in dry summers. Water during droughts and keep the shrub open.
• Few flowers: Usually caused by pruning in spring or too much shade. Prune only after flowering.
• Bare centre: Old shrubs that are never pruned become bare in the middle. Rejuvenate by removing a third of the oldest stems at the base each year.

Through the year

• March: Plant. Add compost.
• April: Plant. Mulch.
• May: Flower buds appear. Watch for aphids.
• June: Full flower: a white cascade. Take softwood cuttings.
• July: Prune straight after flowering: remove a third of the old stems.
• August: Water during long dry spells.
• October: Plant.
• November: Plant. Leaf fall.
• December: Rest. Take hardwood cuttings.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• The species name nipponica means ‘from Japan’: Nippon is the Japanese name for the country.
• Spiraeas belong to the rose family, like apples, cherries and hawthorn.
• It flowers a few weeks later than the white spiraeas that bloom in April–May, extending the white season in the garden.