Persian silk tree

Persian silk tree: how do you recognise it?

Habit

Small tree with one or more trunks and a broad, flat, umbrella-shaped crown; here usually 4–6 m tall and wide.

Leaves

Twice pinnate, up to 30 cm long, with a great many tiny leaflets that fold up at night. It leafs out late, often in June.

Flower

Powder puffs of long pink and white stamens, in July–August at the tips of the branches.

Scent

Sweet and slightly fruity, especially on warm evenings.

Fruit

Flat, light brown pods of 10–15 cm, which often hang on the tree into winter.

Flowering: July–August · Plants: April–June · Pruning: June

Why grow it?

• Exotic flowers in midsummer, long after most trees have finished flowering.
• The fluffy flowers smell sweet and draw in bees and butterflies.
• The airy foliage casts light, dappled shade: ideal above a patio.
• Once established it copes well with drought and heat.
• As a member of the pea family it fixes nitrogen from the air and needs little feeding.

Persian silk tree: where does it grow best?

• Full sun: the warmer it is, the better it flowers. A spot in front of a south-facing wall is ideal.
• Free-draining sandy, loamy or clay soil, acid to chalky. It dislikes wet feet in winter.
• Normal to dry soil: once established it is drought tolerant.
• Sheltered from cold north and east winds.
• Allow 4–6 m for the crown and plant it at least 3 m from buildings.

Light

Sun

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Dry or normal

Size

6 m tall, 6 m wide

Hardiness

Hardy (to -15 °C)

Goes well with

• Lavender: Likes the same sunny, dry spot and flowers at the same time.
• African lily: Blue globes of flowers beneath the pink puffs.
• Feather grass: Swaying stems in a sunny gravel border.
• Catmint: Blue underplanting that tolerates drought and also attracts bees.

Persian silk tree: when and how to plant it?

Plant in April–June.

1. Plant in April, May or June, so it has a whole summer to root in before its first winter.
2. Buy a pot-grown plant: it has a taproot and resents being moved.
3. Dig a hole twice as wide as the root ball. Open up heavy soil with coarse sand or fine gravel.
4. Set the plant at the same depth as in the pot, firm it in and add a stake on the windward side.
5. Water in well straight away, then weekly in dry spells during the first year.
6. Spread a mulch around the base, keeping it off the trunk.

Care

Water

Weekly in dry spells during the first year. After that only in long droughts; in a pot, regularly in summer.

Feeding

Little needed: some compost in spring is enough. Too much fertiliser gives soft wood that does not ripen well before winter.

Patience

It leafs out late, often in June. A bare tree in May is not dead: wait before cutting anything off.

Pots

In a large pot with free-draining compost it can last for years; repot every two to three years in spring.

Tidying

The pods and tiny leaflets drop in autumn; sweep them off the patio or lawn.

Tip: Plant it where you sit on summer evenings: you will see the leaves fold up and smell the flowers. Wait until late June to prune, as it leafs out late.

Persian silk tree: when to prune it?

Pruning months: June.

When: It needs little pruning. Only prune in June, once the leaves are out and you can see which branches have survived the winter.

How:

• Cut frost-killed shoot tips back to living wood, just above a leaf or bud.
• Remove crossing and low-hanging branches to keep a neat umbrella shape.
• On young trees, choose one or a few strong trunks and remove competing shoots.
• Never saw off large branches: big wounds heal poorly.

Caution: Do not prune in winter or early spring: you cannot yet see what is dead, and fresh wounds may be damaged by frost.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Soak the hard seeds overnight in hot (not boiling) water. Sow in April indoors at 20 °C in deep pots; they germinate within a few weeks. Seedlings flower after a few years and do not always resemble the parent.

Root cuttings

In winter, lay 5 cm pieces of root in a pot of sandy cutting compost, kept cool and frost-free. They sprout in spring.

Persian silk tree: how does it get through the winter?

Hardy to −15 °C: protect young plants.

• Hardy to about −15 °C. Older trees survive most Belgian winters in a warm, sheltered spot.
• Young trees are more sensitive: for the first few winters, lay a thick mulch over the roots and wrap the crown in fleece during hard frost.
• Wet soil in winter is more dangerous than cold: make sure drainage is good.
• In a pot: keep it cool and frost-free in winter, for example in an unheated garage; it can be dark, as it is leafless.

Diseases and pests

• Late leafing: In May it is still bare. That is normal: wait until late June before deciding a branch is dead.
• Frost damage: Shoot tips fail to leaf out after a hard winter. Cut them back to living wood in June.
• Root rot: The tree declines and the leaves wilt, on wet, heavy soil. Prevent it with free-draining soil and no watering in winter.
• Aphids and psyllids: Sticky leaves and black sooty mould on the patio below. Hose them off; birds and ladybirds do the rest.

Through the year

• January: Wrap young trees in fleece during hard frost.
• April: Plant. Give some compost.
• May: Plant. Still bare: be patient.
• June: Leaves appear. Cut off dead shoot tips.
• July: In flower. Water young trees in dry spells.
• August: In flower. Scented on warm evenings.
• September: Pods turn brown. Collect seed.
• October: Leaf fall. Stop feeding.
• November: Mulch over the roots of young trees.
• December: Move potted plants somewhere frost-free.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• The leaflets fold up in the evening and in dull weather, as if the tree were going to sleep: hence its Dutch name, ‘sleeping tree’.
• The genus is named after Filippo degli Albizzi, an Italian nobleman who introduced the tree to Europe around the middle of the 18th century.
• The puffs are not petals but dozens of long stamens per floret; the real petals are tiny.