Japanese box

Japanese box: how do you recognise it?

Habit

A compact, dense shrub that slowly reaches about 1 m tall and wide.

Leaves

Small, oval to obovate and glossy green; in cold winters they may turn bronze or orange-tinted.

Flowers

Small yellowish-green flowers without petals in the leaf axils, in April.

Fruit

Small three-horned capsules that split open and shoot out small black seeds.

Roots

Shallow and finely branched: do not hoe deeply around the plant.

Flowering: April · Plants: April–May and September–October · Pruning: June and August

Why grow it?

• Evergreen: a crisp green accent all year round.
• Ideal for low hedges, border edging and topiary balls or blocks.
• Slow-growing, so little work: one or two clips a year are enough.
• Tolerates sun, partial shade and shade and almost any well-drained soil.
• Early flowers in April, a welcome source of nectar and pollen for bees.
• Does well in pots and containers on a patio.

Japanese box: where does it grow best?

• Sun, partial shade or shade; in strong sun the leaves can scorch after clipping.
• Any well-drained soil: sand, loam or clay, acid to chalky.
• Dry to normally moist; waterlogging causes root rot.
• An airy spot helps against box blight: avoid damp, still corners.
• For a low hedge: 5–8 plants per metre, depending on their size.

Light

Sun, partial shade and shade

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Dry or normal

Size

1 m tall, 1 m wide

Hardiness

Hardy (to -20 °C)

Goes well with

• Roses: Box hedges as a crisp frame for a rose bed.
• Lavender: Grey foliage and blue flowers inside a green frame.
• Hosta: Large leaves in shade beside the tiny box leaves.
• Ornamental grasses: Loose, moving plumes beside tight clipped balls.
• Lady’s mantle: Soft green leaves and small yellow flowers spilling over the edge of the hedge.

Japanese box: when and how to plant it?

Plant in April–May and September–October.

1. Plant in April–May or in September–October, when the soil is neither frozen nor waterlogged.
2. For a hedge, dig a trench about 30 cm wide and deep and mix in compost.
3. Set the plants at the same depth as they were in their pots: 5–8 per metre for a hedge.
4. Firm the soil and water generously; keep the soil moist for the first few months.
5. Mulch with compost, but keep the mulch away from the stems.
6. In a pot: choose a pot with a drainage hole and good compost, mixed with a little sand if you like.

Care

Watering

In the first year, water regularly in dry spells. Water pots in winter too, on frost-free days.

Feeding

In March–April, an organic fertiliser or compost; yellow leaves may point to a lack of nutrients.

Mulching

A thin layer of compost in spring keeps the shallow roots cool.

Checking

From April to October, look inside the plant every few weeks for caterpillars and webbing of the box tree moth.

Tools

Disinfect your shears before and after clipping so you do not spread box blight.

Tip: Clip on a dry, overcast day and disinfect your shears: this prevents scorched leaves and stops you spreading box blight. From April to October, check inside the plant every few weeks for box tree moth caterpillars.

Japanese box: when to prune it?

Pruning months: June and August.

When: Clip in June, after the first flush of growth, and again at the end of August if you wish. Choose a dry, overcast day.

How:

• Clip with sharp shears; stretch a string line for a hedge and use a template for a ball if needed.
• Cut the new growth back to just above the previous clipping line.
• Do not clip in bright sun or heat: the inner leaves then scorch easily.
• Do not clip in wet weather and clear up the clippings: this limits box blight.
• Stop clipping after mid-September: late shoots will not harden before winter.

Caution: All parts are poisonous: wear gloves when clipping and do not leave clippings where children or animals can reach them.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Cuttings

In August–September, take 10 cm cuttings of this year’s growth, remove the lower leaves and root them in a mix of cutting compost and sand in a cold frame. They root within a few months.

Layering

In spring, peg a low branch down into the soil; after a year, sever it and transplant it.

Japanese box: how does it get through the winter?

Hardy to −20 °C.

• Hardy to about −20 °C: in open ground it comes through Belgian winters without trouble.
• In cold winters the leaves may turn bronze or orange-tinted; they green up again in spring.
• In a pot: stand it in a sheltered spot, wrap the pot in severe frost and water a little on frost-free days.
• Shake heavy snow off hedges and balls so that the branches do not splay apart.

Diseases and pests

• Box tree moth: Green caterpillars with black stripes and spots that eat leaves and bark, often with webbing. Remove them or blast them out with a strong jet of water; a biological product based on Bacillus thuringiensis also helps. Pheromone traps show when the moths are flying.
• Box blight: Brown leaf spots, leaf drop and black streaks on the twigs, especially in warm, humid weather. Cut out affected parts, put them in the household waste and keep the foliage as dry as possible.
• Box sucker: Cupped, curled leaves at the shoot tips in spring. Hardly harmful: the June clip removes them.
• Scorched leaves: Brown leaves after clipping in full sun or from cold, drying winds. Clip on an overcast day and shelter pots from bitter wind.
• Yellow leaves: Caused by a lack of nutrients or soil that is too wet. Feed and make sure the soil drains well.

Through the year

• March: Feed. Check hedges and pots after winter.
• April: In flower. Plant. Check for box tree moth.
• May: Plant. Look for box tree moth caterpillars.
• June: First clip on an overcast day.
• July: Check for box tree moth. Water in dry spells.
• August: Second clip at the end of August if needed. Take cuttings.
• September: Plant. Take cuttings. Check for box tree moth.
• October: Plant. Clear up clippings and fallen leaves.
• December: Protect pots in severe frost. Shake off snow.

Edible and useful

Not edible. All parts of box are poisonous, especially the leaves: their alkaloids cause vomiting, stomach ache and diarrhoea, and in larger amounts convulsions too. The greatest danger is the clippings: trimming a hedge or topiary ball leaves behind plenty of twigs and leaves. Horses, sheep, goats and other livestock can become seriously ill or even die if they find or are given clippings; dogs, especially young dogs that chew twigs, and cats can fall ill from them too. Clear up the clippings straight away, never throw them into a field, run, pen or hutch, and do not give them to rabbits or guinea pigs; if an animal has eaten some, call your vet. The blessed sprigs of ‘palm’ handed out in Flanders on Palm Sunday are box too: hang them out of reach of small children and pets. Wash your hands after clipping. If any is swallowed, call a poison centre (in Belgium 070 245 245) or your doctor at once.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• Boxwood is very hard and fine-grained; it was once used for wood engravings, chess pieces and flutes.
• The box tree moth comes from East Asia and was first found in Europe around 2007; it now occurs throughout Belgium.
• Box has separate male and female flowers on the same plant, both without petals.