Kentucky yellowwood

Kentucky yellowwood: how do you recognise it?

Habit

Medium-sized tree 10–15 m tall and 8–10 m wide with a broad, round crown.

Leaves

Odd-pinnate with 7–11 leaflets, up to 30 cm long; fresh green, bright yellow in autumn. The leaves appear fairly late.

Flower

Hanging, 20–30 cm long panicles of fragrant white pea-like flowers in June.

Bark

Smooth and grey like beech, even on older trees.

Fruit

Flat, thin pods 5–8 cm long holding a few seeds, ripe in autumn.

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

Why grow it?

• Hanging clusters of sweetly scented white flowers in June, like wisteria but on a tree.
• Bees and bumblebees visit the flowers: a good nectar source in June.
• Smooth grey bark and elegant, feathery leaves give the tree character all year.
• Bright yellow autumn colour.
• A handsome tree for medium to large gardens, with a broad crown that does not cast too dense a shade.

Kentucky yellowwood: where does it grow best?

• Sun to half shade; it flowers best in sun.
• Free-draining, fertile soil: sand, loam or clay, acid to chalky.
• Evenly moist; tolerates short dry spells once established, but not standing water.
• Sheltered from strong winds, because the wood is fairly brittle.
• Allow 8–10 m of space around the trunk, including from buildings.

Light

Sun and partial shade

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Normal

Size

12 m tall, 10 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Hosta: Large leaves under the tree, in the same light shade.
• Ferns: A fresh, green underplanting beneath the crown.
• Cranesbill: A tough ground cover that grows well under trees.
• Hellebore: Flowers early in the year beneath the still-bare tree.
• Snowdrop: Bulbs that flower in spring before the tree comes into leaf.

Kentucky yellowwood: when and how to plant it?

Plant in March–April and October–December.

1. Plant in March–April or from October to December, when the soil is neither frozen nor waterlogged.
2. Dig a hole two to three times as wide as the root ball and just as deep. Loosen the bottom and sides.
3. Set the tree at the same depth as in its pot or nursery, with the root collar at soil level. Backfill with loose soil and a little compost.
4. Put in a stake and tie the tree loosely; remove the tie after two to three years.
5. Water in with 20–30 litres straight away and spread 5–8 cm of mulch around the base, keeping it off the trunk.

Care

Water

For the first two to three years, a good soaking (20–30 litres) every week in dry weather. After that the tree usually copes by itself.

Feeding

A spade of compost around the tree in spring; chemical fertiliser is not needed.

Mulching

A layer of leaf mould or bark keeps the soil moist; keep the trunk itself clear.

Training

On young trees, keep a strong central leader and remove weak, narrow forks early.

Flowering

Young trees often flower only after a few years, sometimes ten, and not equally richly every year.

Tip: Prune Kentucky yellowwood only in summer and give young trees one strong leader: this prevents both bleeding and branch breakage.

Kentucky yellowwood: when to prune it?

Pruning months: July–August.

When: In summer, in July–August, when the tree is in full leaf. Do not prune it in winter or spring.

How:

• Limit yourself to formative pruning in the first years: choose one strong leader and remove competing tops.
• Remove branches with a narrow, V-shaped fork or keep only one of them: such forks split easily later.
• Take out dead, damaged and crossing branches.
• Keep cuts small: better a few small branches than one thick one.

Caution: Do not prune in spring: the tree bleeds heavily. It has brittle wood and weak forks, so give it a good structure.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Collect the pods in autumn and sow the seeds, which have a hard coat, after soaking overnight and nicking them lightly. Sow outdoors in autumn or spring in open ground; a seedling takes many years to flower.

Root cuttings

In winter: lay pieces of root 5–8 cm long horizontally in sandy compost and keep them frost-free. Success can be variable.

Kentucky yellowwood: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy to about −30 °C: no protection is needed in Belgium.
• Young trees: keep the stake and tie in order and lay a mulch around the base to prevent drying out.
• The tree is bare in winter; the smooth grey trunk and fine twigs then show up well.

Diseases and pests

• Branch breakage: Branches with a narrow fork snap in storms or under a heavy load of flowers. Give a good structure and prune young trees early.
• Bleeding: Pruning in spring makes a lot of sap run from the wound. So prune in July–August.
• Late leafing: The tree leafs out fairly late, sometimes not until May. Do not worry: as long as the twigs are green under the bark, it is alive.
• Little or no flowering: Young trees do not flower yet; older trees flower erratically. Give sun and enough water, but no nitrogen-rich fertiliser.
• Drought stress: Curled, limp leaves in a dry summer. Water young trees generously and mulch the base.

Through the year

• January: Check stake and tie. Do not prune.
• March: Plant or move. Put compost around the tree.
• April: Plant. Apply or top up the mulch.
• May: Late leafing. Water young trees in dry weather.
• June: Fragrant flower clusters. Bees and bumblebees visit the flowers.
• July: Summer pruning. Water young trees in dry weather.
• August: Last chance to prune. Water in dry weather.
• September: Pods ripen; collect seed if you like.
• October: Yellow autumn colour. Plant.
• November: Leaf fall. Top up the mulch.
• December: Rest. Planting is possible as long as the soil is not frozen.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• The heartwood is yellow and was once used to dye cloth yellow; hence the name yellowwood.
• The genus name Cladrastis comes from the Greek ‘klados’ (branch) and ‘thraustos’ (brittle) and refers to the brittle wood.
• The tree has smooth grey bark like a beech, even when old.