Seven-son flower

Seven-son flower: how do you recognise it?

Habit

Large, deciduous, multi-stemmed shrub or small tree 4–6 m tall and about 3 m wide, with an open, arching crown.

Leaves

Opposite, long oval to lance-shaped, 8–12 cm long, with three clear veins; dark green.

Flower

Panicles of small, white, fragrant flowers at the tips of the new shoots, from August to October.

Calyx

After flowering the calyces enlarge and turn rosy red; they decorate the plant into autumn.

Bark

Light brown to grey, peeling in long strips; very decorative in winter.

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

Why grow it?

• Fragrant white flowers in late summer, when few other shrubs flower.
• Afterwards the calyces turn rosy red, so the display carries on for weeks.
• The flowers are a source of nectar for bees and butterflies, just late in the season.
• Peeling, pale bark gives structure all year, even in winter.
• Grows into a multi-stemmed shrub or small tree; ideal as a specimen in a large garden and not prone to disease.

Seven-son flower: where does it grow best?

• Sun or part shade; in full sun it flowers most freely.
• Ordinary, well-drained garden soil: sandy, loamy or clay, acid to chalky.
• Normally moist: once established it is fairly drought tolerant, but it flowers better with regular water.
• A spot sheltered from strong wind helps; allow plenty of room: give it 3–4 m of free space.
• Lovely as a specimen, in a large border or as a backdrop for lower plants.

Light

Sun and partial shade

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Normal

Size

5 m tall, 3 m wide

Hardiness

Hardy (to -25 °C)

Goes well with

• Ornamental grasses: Late summer plumes that go well with the white and rosy red flowers.
• Stonecrop: Stays low and flowers at the same time, often pink.
• Japanese anemone: Pink or white flowers in autumn, beneath the shrub in part shade.
• Panicle hydrangea: Another late-flowering shrub that combines well.
• Michaelmas daisy: Blue and purple flowers for contrast in autumn.

Seven-son flower: 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 as deep as the root ball and twice as wide; mix some compost into the soil you dug out.
3. Set the plant at the same depth as in its pot and firm the soil well.
4. Plant 3–4 m from buildings and other shrubs; in a row for a hedge, 1.5–2 m apart.
5. Water well straight away and keep the soil moist for the first two years.
6. Spread a 5–8 cm layer of mulch around the base, without touching the stem.

Care

Watering

In the first two years, weekly in dry weather. After that only in long dry spells.

Feeding

Compost or an organic shrub fertiliser in spring. Not after July.

Mulching

A layer of leaf mould or bark in spring keeps the soil cool and moist.

Spent flowers

Do not cut them off: the rosy red calyces are the best part.

Support

A young tree form gets a sturdy stake for the first years; a multi-stemmed shrub does not.

Tip: Fragrant white flowers in September, then the calyces turn pink. It grows into a large, multi-stemmed shrub with peeling bark. Give it room and prune in February–March.

Seven-son flower: when to prune it?

Pruning months: March.

When: From late February to late March, before the new shoots start. It flowers on new wood.

How:

• Remove dead, damaged and crossing branches right down to the base.
• For a tree form, keep one or a few strong stems and remove side shoots at the base; for a shrub, keep the multi-stemmed shape.
• For a more compact plant you can shorten the longest branches by a third.
• Thin overcrowded shrubs by removing a few of the older branches right at the base.

Caution: Do not prune after July: that costs flower buds and new shoots that can no longer ripen before winter.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Softwood cuttings

In June–July: take 10–15 cm cuttings from non-flowering shoots, remove the lower leaves and insert in moist sandy compost under plastic. They root in a few weeks.

Seed

Sow outdoors in autumn in a tray or cold frame; the seed needs a cold spell to germinate. Seedlings grow slowly.

Seven-son flower: how does it get through the winter?

Hardy to −25 °C.

• Fully hardy, down to about −25 °C: no protection is needed in Belgian winters.
• Young plants get a layer of mulch around the base for the first winters, to protect the roots.
• The peeling bark is especially attractive in winter: leave the stems uncluttered.

Diseases and pests

• Frost damage to tips: Young shoots can freeze in a late night frost. Cut them back in spring to healthy wood.
• Poor flowering: Usually too much shade or pruning too hard. Give more sun and prune in February–March.
• Aphids: Sometimes on young shoots. Ladybirds usually clear them up; otherwise a jet of water.
• Powdery mildew: White powder on the leaves in hot, dry summers. Water at the base, leave space and cut off affected shoots.

Through the year

• March: Prune. Apply compost. Plant.
• April: Plant. Mulch.
• June: Take softwood cuttings.
• July: Water in dry weather. Take cuttings.
• August: Flowering begins. Bees and butterflies visit the flowers.
• September: Full, fragrant flower. Then the calyces turn rosy red.
• October: Rosy red calyces. Plant.
• November: Plant. Mulch young shrubs.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• Heptacodium was only introduced to Western gardens in 1980, through a Chinese–American plant expedition organised by the Arnold Arboretum.
• In the wild the species now survives in only a few places in eastern China.
• The name comes from the Greek ‘hepta’ (seven): the flowers often sit together in groups of seven in a small head. In English it is called ‘seven-son flower’.