Chaste tree

Chaste tree: how do you recognise it?

Habit

Wide, open shrub or small multi-stemmed tree, 2–2.5 m high and wide, with upright branches.

Leaves

Palmate, made up of 5–7 narrow leaflets of 5–10 cm; grey-green with a paler underside. It leafs out late, often not until May.

Flowers

Narrow lilac-blue spikes of about 10–20 cm in August–September.

Scent

Flowers and leaves smell spicy, especially when rubbed.

Fruit

Small, dark, peppercorn-like fruits, usually only after a warm summer.

Flowering: August–September · Plants: April–May · Pruning: March

Why grow it?

• Flowers late, in August–September, just when the border starts to tire.
• Lilac-blue flower spikes with a spicy scent; the leaves are aromatic too when you rub them.
• A magnet for bees and butterflies in late summer.
• Drought tolerant: a good choice for a sunny, dry corner, a terrace or a gravel garden.
• Brings a Mediterranean feel to the garden, lovely beside lavender and ornamental grasses.

Chaste tree: where does it grow best?

• Full sun and warmth: the sunnier the spot, the richer the flowering. A south- or west-facing wall is ideal.
• Well-drained sandy or loamy soil, acid to chalky. Poor, dry soil suits it well.
• Dry to normal; waterlogged soil, especially in winter, causes root rot.
• Sheltered from cold east winds; in Flanders a warm spot against a wall is the safest.
• Allow 2–2.5 m of space per plant.

Light

Sun

Soil type

Sand or loam

Acidity

Not fussy

Moisture

Dry

Size

2.5 m tall, 2.5 m wide

Hardiness

Hardy (to -15 °C)

Goes well with

• Lavender: Likes the same sun and dry soil; purple flowers and scent too.
• Stonecrop: Flowers at the same time and attracts bees and butterflies too.
• Coneflower: Pink flowers in late summer beside the lilac spikes.
• Ornamental grasses: Plumes and soft lines make an airy foreground.

Chaste tree: when and how to plant it?

Plant in April–May.

1. Plant in April–May so that it can root well before winter.
2. Choose a spot in full sun and dig a hole twice as wide as the root ball.
3. Make heavy or wet soil more free-draining with coarse sand or grit; compost is hardly needed.
4. Set the plant at the same depth as in its pot and firm the soil.
5. Water thoroughly straight away, then weekly in dry weather in the first year.
6. Spread a 5 cm layer of bark or compost mulch, keeping it clear of the stem.

Care

Water

In the first year, weekly in dry weather, after that only in long dry spells. Too much water causes rot.

Feeding

Little: some compost in April is enough. Too much fertiliser gives lots of leaves and few flowers.

Mulching

In November, a thick layer (10–15 cm) of leaves, straw or bark around the base protects the roots from frost. Remove it in April.

Spent flowers

Cut off the faded spikes: this keeps the shrub tidy and may give a second, smaller flush.

Tip: Prune it hard every spring and give it the warmest spot in the garden, preferably against a south-facing wall. It will then flower richly year after year.

Chaste tree: when to prune it?

Pruning months: March.

When: In March to early April, as soon as the buds swell and you can see what is still alive.

How:

• First cut out dead branches and frost damage back to healthy, green wood.
• Cut the rest back hard, to 2–3 buds above the old wood, or to 30–50 cm above the ground.
• Remove weak and crossing branches completely.
• Do this every year: it flowers on new wood.

Caution: Do not prune in autumn, because young shoots are easily killed by frost then. Wait until March: the buds show which wood is still alive.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Semi-ripe cuttings

In July–August: take 10–12 cm cuttings with a small piece of old wood, remove the lower leaves and insert them in sandy compost under plastic in a warm, bright spot. They root after a few weeks.

Seed

Sow the seed in autumn or spring in a warm place. Germination is slow and erratic; seedlings only flower after a few years.

Chaste tree: how does it get through the winter?

Hardy to −15 °C: protect young plants.

• Hardy to about −15 °C: in Flanders usually fine, but in severe winters it may freeze back to the ground.
• Frozen back? It usually shoots again from the base, often not until May–June. So wait before you remove anything.
• Give young plants a thick layer of mulch (10–15 cm) and horticultural fleece around the branches for the first winters.
• In a pot: put it in a bright, frost-free place.

Diseases and pests

• Frozen branches: Brown, dry branches in spring after a severe winter. Wait until May–June, then cut back to healthy wood; it often shoots from the base.
• Few flowers: Caused by too little sun, soil that is too wet or too rich, or a cool summer. Move it to a warmer spot and prune every spring.
• Root rot: The shrub declines and the leaves wilt despite moist soil. Caused by wet, heavy soil; improve drainage with sand or grit.
• Late leafing: It does not leaf out until May. That is normal and no reason to worry.

Through the year

• March: Prune to 2–3 buds above the old wood or to 30–50 cm. Apply compost.
• April: Plant. Remove the winter mulch protection.
• May: Plant. The shrub leafs out late: be patient.
• June: Water in dry weather. Remove frozen branches.
• July: Take semi-ripe cuttings.
• August: First flowers: lilac spikes, bees and butterflies arrive.
• September: Full bloom. Remove faded spikes.
• November: Lay a thick layer of mulch around the base.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• Its other name, monk’s pepper, comes from the peppery little fruits, which are said to have been used as a spice in monasteries.
• The palmate leaves look like those of hemp, but the plant is not related to it: it belongs to the mint family (Lamiaceae).
• It only flowers at the end of summer, on new shoots of the current year.