Kentucky coffeetree

Kentucky coffeetree: how do you recognise it?

Habit

Tree 15–20 m tall and 10–12 m wide, with an open crown and stout, blunt twigs that are sparsely branched.

Leaves

Twice-pinnate, 60–90 cm long, with dozens of small leaflets; pinkish bronze when emerging, later blue-green and yellow in autumn.

Flower

Greenish-white flowers in clusters in May–June; male and female flowers are on different trees.

Fruit

On female trees: thick, brown, leathery pods 15–25 cm long with hard seeds in sticky pulp.

Bark

Dark grey and furrowed, with scaly ridges that curl outwards.

Flowering: May–June · Plants: March–April and October–December · Pruning: January–February

Why grow it?

• Striking, rugged outline: even bare in winter it is sculptural and distinctive.
• Huge, twice-pinnate leaves that emerge pinkish bronze in spring and turn yellow in autumn.
• Very tough: tolerates drought, urban pollution and poor soil once established.
• Because it leafs out late, plenty of light reaches the plants beneath in spring.
• A special tree for anyone looking for something different from the usual limes and maples.

Kentucky coffeetree: where does it grow best?

• Full sun; it grows poorly in shade.
• Deep, free-draining soil: sand, loam or clay, acid to chalky. Tolerates poor and dry soil.
• Dry to moderately moist; preferably not long-term wet soil.
• Allow 10–12 m of space, including from buildings, and do not plant it where children or livestock can pick up the pods.

Light

Sun

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Dry or normal

Size

18 m tall, 12 m wide

Hardiness

Hardy (to -35 °C)

Goes well with

• Daffodil: Flowers in spring beneath the still-bare tree, before the leaves emerge.
• Hellebore: Enjoys the dappled light the late-leafing tree gives in spring.
• Cranesbill: A tough ground cover that grows well in the root zone.
• Ferns: A fresh underplanting for summer shade.
• Ornamental grasses: Soft plumes contrast with the stout, rugged branches of the tree.

Kentucky coffeetree: 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.
4. Put in a stake and tie the tree loosely; remove the tie after two to three years. Choose a young tree: older ones transplant badly because of the deep taproot.
5. Water in with 20–30 litres straight away and spread mulch around the base, keeping it off the trunk.

Care

Water

For the first two to three years, a good soaking every week in dry weather. After that the tree usually copes by itself, even in dry summers.

Feeding

Usually not needed. A spade of compost in spring on poor soil can help.

Mulching

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

Clearing up

The leaves fall early and consist of small leaflets and large leaf stalks. On female trees the pods fall in winter and spring; clear them away.

Protection

Young trees may be gnawed by rabbits or deer; a tree guard helps.

Tip: Choose a male tree if you do not want pods and plant it in full sun with plenty of space; it has a taproot and transplants badly.

Kentucky coffeetree: when to prune it?

Pruning months: January–February.

When: As little as possible. If needed: in January–February, on a frost-free day, while the tree is dormant.

How:

• Young trees: choose one central leader and remove competing tops.
• Take out dead, damaged and crossing branches.
• Do not cut back the top: the tree has few branches and recovers slowly from hard pruning.
• Do not leave stubs; cut just outside the branch collar.

Caution: Do not cut the tree back: it branches sparingly by nature and hard pruning ruins its rugged shape.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

The seeds have a very hard coat. File them lightly or soak them for a day in hot (not boiling) water until they swell; sow in spring in deep pots, because the taproot grows quickly. The sex of the tree only shows much later.

Root cuttings

In winter: lay pieces of root 5–8 cm long horizontally in sandy compost and keep them frost-free. This is a way of cloning a male tree.

Kentucky coffeetree: how does it get through the winter?

Hardy to −35 °C.

• Fully hardy to about −35 °C: no protection is needed in Belgium.
• Young trees: keep the stake and tie in order and lay a mulch around the base.
• In winter the tree is bare with stout, blunt twigs; female trees often keep their pods until late winter.

Diseases and pests

• Pods and seedlings: Female trees drop many pods, and seedlings may appear. Clear the pods and pull up seedlings; or choose a male tree.
• Late leafing: It leafs out late, often not until the end of May, and looks dead until then. Scratch a twig with your fingernail: if it is green, the tree is alive.
• Wet feet: In waterlogged, heavy soil it declines. Choose a free-draining spot or improve drainage.
• Animal damage: Rabbits and deer gnaw the bark of young trees. A tree guard or mesh protects it until the trunk is thick enough.

Through the year

• January: Prune if needed on a frost-free day. Clear pods.
• February: Prune if needed on a frost-free day.
• March: Plant. Put compost around the tree.
• April: Plant. Apply or top up the mulch.
• May: Late leafing, pinkish bronze. Flowering begins.
• June: Greenish-white flower clusters. Water young trees in dry weather.
• July: Water young trees in dry weather.
• September: Pods ripen on female trees. Keep the seeds away from children and animals.
• October: Yellow autumn colour. Plant.
• November: Early leaf fall. Clear up.
• December: Rest. Planting is possible as long as the soil is not frozen.

Edible and useful

Not edible. The pods, sticky pulp and seeds of Kentucky coffeetree are poisonous: they contain cytisine, an alkaloid that causes vomiting, stomach ache, diarrhoea and, in larger amounts, trembling and seizures if eaten. In North America the roasted seeds were once used as a coffee substitute, but never try it yourself: raw or underroasted they are dangerous. Pick up fallen pods, especially where children play, and do not plant the tree near a play area or a field: livestock and horses can become seriously ill from them. Keep dogs and cats away from the pods too. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Did you know?

• The name Gymnocladus comes from the Greek ‘gymnos’ (naked) and ‘klados’ (branch), because of its bare winter branches.
• The common name ‘Kentucky coffeetree’ recalls settlers who used the roasted seeds as a coffee substitute, which you should not copy: they are poisonous.
• The twice-pinnate leaves are up to 60–90 cm long and are among the largest compound leaves of trees hardy in our climate.