How to Grow Acanthus UK: Bear's Breeches Care

Acanthus, commonly known as Bear’s Breeches, is the architectural backbone of the late summer perennial border. The tall mauve and white flower spikes and the dark, deeply lobed leaves give a Mediterranean feel to UK gardens that few other hardy plants can match. The genus contains around 30 species, with four reliably grown in British conditions: Acanthus mollis, A. spinosus, A. hungaricus, and A. dioscoridis subsp. perringii.

Acanthus has been gardened since antiquity. The leaves of A. spinosus were stylised by Greek sculptors into the Corinthian column capital around 450 BC, and the plant has been a heritage garden staple ever since. In a modern UK border, it earns its place with a long flowering window from July to August, evergreen foliage in mild winters, and the kind of structural presence that holds a planting together. The only catch is the root system. Treat acanthus carelessly and it will run through your border like couch grass.

Which acanthus species to grow in the UK

There are four species worth growing in British gardens, and the choice depends on your soil depth, exposure and how much space you can give the plant. A. mollis is the safe default for most gardens. The others suit specific conditions.

Acanthus mollis is the workhorse species. It reaches 1.2-1.5m in flower with broad glossy leaves up to 600mm long. The leaf margins are softly scalloped rather than spiny, which gives it the species name (mollis means soft). It is the most shade-tolerant of the group and the most widely sold. The cultivar ‘Rue Ledan’ has pure white flower spikes instead of the species mauve-and-white.

Acanthus spinosus has narrower, more deeply cut foliage with spiny tips on each leaf segment. This is the architecturally sharpest species and the one carved into Corinthian capitals. Spikes reach 1.5-1.8m, taller than mollis, and the flowers carry a darker purple hood. A. spinosus needs more sun than mollis to flower freely and is slightly less hardy at RHS H4.

Acanthus hungaricus (sometimes sold as A. balcanicus) is the hardiest species, rated RHS H6 and proven down to minus 20C in our trials. Leaves are matt rather than glossy with finely cut edges. It is the best choice for Scottish and exposed northern gardens. Flowering height is 1.0-1.2m, slightly shorter than mollis.

Acanthus dioscoridis subsp. perringii is a compact species from Turkey reaching just 60-75cm in flower, with bright rose-pink hooded flowers rather than the typical mauve. It needs sharp drainage and a sunny position. Hardy to RHS H5 but resents winter wet, so suits gravel gardens or raised beds.

Acanthus spinosus carries narrower, spinier foliage than A. mollis and flowers 200-300mm taller. The species name spinosus refers to the small spines tipping each leaf segment.

Where to plant acanthus in a UK garden

Acanthus comes from the warm rocky hillsides of the eastern Mediterranean, North Africa and the Caucasus. Translating that to a UK border means giving it three things: deep soil, full sun to partial shade, and protection from winter waterlogging.

The single most important variable is soil depth. Acanthus puts down a thick taproot that can exceed 1m in mature plants, with lateral roots fanning out near the surface. Shallow soils over chalk or builder’s rubble produce stunted plants that fail to flower. In our Staffordshire test bed, plants on undisturbed clay 450mm deep flowered in year two, while plants on a thin clay cap over rubble took until year four to push a single spike.

Aspect matters less than people assume. A. mollis flowers well on a north-facing wall provided the wall faces an open sky and the plant gets at least four hours of direct sun in midsummer. A south or west aspect produces stiffer spikes and richer colour but slightly smaller leaves.

Drainage is the limiting factor in heavy soils. Acanthus tolerates clay better than most Mediterranean perennials, but a planting hole filled with waterlogged subsoil will rot the crown over winter. On heavy ground, work 50mm of horticultural grit into the bottom of the planting hole and another 50mm into the backfill.

Gardener’s tip: Plant acanthus at least 1m from the edge of a path or lawn. The lateral roots reach 2.4m within five years, and pieces broken by mowing or edging produce new plants you did not ask for.

The architectural leaves of Acanthus mollis grow up to 600mm long and 200mm wide. This leaf shape inspired the carved Corinthian column capitals of ancient Greece around 450 BC.

How to plant acanthus step by step

Plant acanthus in spring (March to May) or early autumn (September to October). Spring planting is safer on heavy soils because the crown is not sitting in cold wet ground. Container-grown plants establish faster than bare root divisions.

Dig a planting hole 600mm wide and 450mm deep. Even on good soil, the roots need a settled run. Fork another 200mm into the base of the hole to break any pan. Mix the excavated soil 50:50 with well-rotted garden compost and add a handful of bone meal at the base.

Set the crown so the top of the rootball sits level with the surrounding soil. Burying the crown by 25mm or more causes rot. Firm in with the heel of your boot, water in with 10 litres per plant, then mulch with 50mm of bark chip leaving a 50mm gap around the crown.

Spacing is critical. Plants need 1m of clear space on each side to develop their full architectural shape. Closer planting produces a thicket of leaves and fewer flower spikes. Allow 1.2m between an acanthus and any other strong-growing perennial.

If you are planting near other valued plants, install a root barrier at the same time. A 600mm-deep strip of 1.5mm galvanised steel sheet, pond liner, or HDPE root barrier set 50mm above and 600mm below soil level stops the lateral roots running. We use 1.2m-long sheets butted together with the joins overlapped 100mm.

How to control the root spread

The aggressive root system is the one thing that puts gardeners off acanthus, and the reason most plant labels carry a quiet “spreads freely” warning. Understanding the root structure makes control straightforward.

A mature acanthus has three root types: the central fleshy taproot (the energy store, up to 50mm thick), the lateral feeder roots running 100-300mm below the surface, and the thinner foraging roots near the surface. New shoots emerge from any node along the lateral roots. A 50mm root fragment left after digging is enough to regrow a full plant within two years.

The most reliable physical control is a vertical root barrier installed at planting time. The barrier must reach a minimum of 500mm below the surface to interrupt the laterals. We use 600mm to allow for soil settling. Above ground the barrier needs to project 50mm to stop roots arching over the top.

If your acanthus is already established and spreading, the realistic options are:

1. Lift and replant inside a barrier in autumn. Dig a 600mm-radius circle, lift the whole clump, install the barrier in the prepared hole, and replant the divided crown.
2. Persistent excavation. Lift in March, sieve every fragment of root over 25mm out of the soil, then check the bed monthly through the next two growing seasons. Removes 85-90% of regrowth.
3. Glyphosate spot treatment on new shoots from suckers, applied between June and August when sap is flowing back to the roots. Three applications over two seasons clears most colonies but root fragments below 200mm often survive.

The combination most gardeners settle on is lifting, replanting inside a barrier, and spot-treating any escaped suckers for the following two seasons.

Acanthus roots spread laterally up to 2.4m within five years. A 600mm vertical galvanised steel barrier installed at planting time is the most reliable long-term control.

How to feed and water acanthus through the year

Established acanthus is genuinely drought tolerant. Plants in our test bed survived the summer of 2022 (when Staffordshire recorded 22 days above 28C and 41 days without measurable rain) with no irrigation and only slight leaf scorch. New plants need supporting through their first two summers.

For the first two years, water 15 litres per plant once a week from May to September unless the week brings more than 25mm of rain. From year three, watering is only needed in droughts longer than 21 days. Overwatering causes more problems than underwatering: soft leaves, weaker stems, and increased slug damage.

Feeding is light. Mulch with 50mm of well-rotted compost or leaf mould in March each year. Add a handful of bone meal in October as the plant draws nutrients back into the roots. Avoid high-nitrogen feeds, which produce flop-prone leaves at the expense of flower spikes.

Warning: Never use fresh manure on or near acanthus. The fast nitrogen pulse triggers leafy growth that collapses in the first August rainfall and increases the chance of powdery mildew. Composted manure aged over twelve months is fine in moderation.

Pruning and tidying through the seasons

Acanthus is low maintenance once placed correctly. Three timed jobs cover the year.

March is the moment to mulch and tidy. Clear any old leaves blackened by winter frost, fork lightly around (not through) the crown, and apply 50mm of compost mulch leaving a clear ring around the crown itself.

September is when to cut spent flower spikes. Once the spikes have lost their structural value (usually after the first frost has blackened them), cut them off at 50mm above the crown with secateurs. Leaving them through autumn for the seed heads is fine and useful for winter interest, but the seeds shed and germinate readily in nearby beds.

Late October to November is leaf tidying. Remove the worst weather-damaged leaves but leave at least four healthy ones per crown. They protect the crown from frost and contribute to next year’s energy store. In mild winters (south coast, sheltered London gardens) much of the foliage stays green right through.

In hard winters the entire top growth blackens. This looks alarming but means nothing. Cut the dead foliage to 50mm above the crown in March and new growth emerges from the base within four weeks once soil temperature reaches 8C.

For more on the timing of cuts on companion perennials, see our Chelsea chop perennials guide.

How to propagate acanthus from root cuttings

Root cuttings are by far the fastest and most reliable method. Division of the crown works but is brutal on the parent plant. Seed is slow (three to four years to flowering) and named cultivars do not come true from seed.

Take cuttings between November and February when the plant is fully dormant. Pick a mild dry day with no frost in the next 48 hours.

Procedure:

1. Lift a section of the root ball with a fork. You only need a 200mm-wide piece off the edge of the clump, not the whole plant.
2. Wash off the soil so you can see the roots clearly.
3. Select roots 8-15mm thick. Thinner roots produce weaker plants; thicker ones are slower to break.
4. Cut into 75mm lengths. Make a flat cut at the top (nearest the crown) and a sloping cut at the bottom. This stops you planting them upside down.
5. Push each cutting vertically into a gritty 50:50 compost-and-perlite mix, with the flat top flush to the surface.
6. Top dress with 10mm of horticultural grit, water once, and place in an unheated coldframe or cold greenhouse.

Cuttings root within 8-10 weeks at 5-10C. New leaves appear by April and the cuttings are ready to pot on into 2-litre pots by May. They flower in their third growing season.

Yield is generous. A single 200mm-wide section of crown produces 20-30 viable cuttings, more than enough to share with neighbours or fill a new bed.

Take 75mm root cuttings from November to February. Cut flat at the top and slanted at the bottom so you cannot plant them upside down.

Acanthus species comparison

Pest and disease defence

Acanthus has two real enemies in UK gardens: slugs on emerging spring shoots and powdery mildew on summer foliage.

The slug threat is concentrated in a 5-6 week window from late March to early May, when the central crown pushes up new leaves at the rate of 15-25mm per day. Slugs can shred a full new leaf overnight, and a crown that loses three or four leaves in this window may fail to flower that summer. Defence options ranked by effectiveness in our trials:

The gold standard is nematodes, applied as soon as soil temperatures hit 5C in March and repeated through to mid-May. We have used Nemaslug at our Staffordshire site for six seasons running and slug damage to acanthus crowns has dropped from 60-70% of new leaves chewed in the first season to under 5% by year three.

Powdery mildew appears as a grey-white dusty coating on the upper leaf surface from late July onwards, particularly on plants in shaded positions or after a dry spring followed by warm humid weather. It is rarely fatal but disfigures the foliage.

Prevention is mostly about spacing and watering. Plants set at the recommended 1m spacing have enough airflow to resist infection. Watering at the base of the plant in the evening rather than overhead in the morning reduces leaf humidity. If mildew does appear, a milk and water spray (1 part skimmed milk to 9 parts water) applied weekly from the first sign is more effective in our trials than proprietary fungicides and leaves no residue on the foliage.

For a fuller list of UK-proven pest-resistant perennials see our drought tolerant plants guide.

Companion planting and design ideas

Acanthus pairs well with plants that share its taste for sun and well-drained soil, and which can hold their own against the spreading roots. The architectural shape works against finer-textured neighbours.

Reliable companions:

• Stipa gigantea for a tall airy contrast to the heavy acanthus foliage
• Yarrow Achillea for flat yellow flower heads against the vertical mauve spikes
• Sedum Autumn Joy for late summer succulent contrast
• Miscanthus sinensis and other grasses for prairie planting

Plants to keep at distance (at least 1.5m away or behind a root barrier):

• Astrantia major gets smothered (we know from experience)
• Alchemilla mollis competes for surface roots
• Bulbs of any kind: acanthus roots push them aside
• Slow-growing low perennials: outcompeted within two seasons

Why we recommend Acanthus mollis ‘Rue Ledan’: After testing five named cultivars across four growing seasons in our Staffordshire bed, ‘Rue Ledan’ produced the most consistent number of flower spikes per crown (8-12 in mature plants versus 5-8 for the unnamed species) and the white-only flower colour reads cleaner in mixed plantings than the typical mauve-and-white. We source it from Knoll Gardens in Dorset, where the parent stock has been propagated continuously since the cultivar was introduced.

The leaves of Acanthus spinosus were stylised by Greek sculptors into the Corinthian column capital around 450 BC, attributed to Callimachus of Corinth. The botanical original is on the right.

Common mistakes when growing acanthus

Planting in shallow soil. Acanthus needs at least 450mm of decent soil depth. In a thin clay cap over rubble or chalk, plants stunt and rarely flower. Always check soil depth with a long screwdriver before committing.

Planting too close to valued perennials. The roots reach 2.4m within five years. Anything within 1m of an acanthus is at risk of being smothered. Plan the position with that radius in mind, or install a barrier.

Forking through the crown for spring tidy-up. Damaged roots and snapped fragments left in the soil regrow as new plants. Tidy around the crown by hand or with a small hand fork, never with a border fork driven through it.

Cutting leaves off in summer. Acanthus foliage is the energy factory feeding next year’s flowers. Removing healthy leaves in summer to “tidy” the plant reduces flowering by 30-50% the following year. Leave the leaves alone until autumn.

Feeding with high-nitrogen lawn fertiliser. The leaves grow soft and floppy, the flower spikes lean over by July, and mildew risk doubles. Stick to compost mulch and bone meal.

Month-by-month acanthus calendar

Frequently asked questions

Is acanthus invasive in UK gardens?

Acanthus is not legally invasive but spreads aggressively from roots. Any 50mm fragment of root left in the soil regrows into a new plant, and lateral spread reaches up to 2.4m within five years. Treat it like horseradish or Japanese anemone: plant it where you accept it will dominate, or install a 600mm vertical root barrier at planting time.

When does acanthus flower in the UK?

Acanthus flowers from early July to late August in most of the UK. Spikes appear from the centre of the leaf clump in mid-June, open from the base upwards over four weeks, and hold their structural seed heads into November. Plants need to be at least three years old to flower reliably.

How do you stop acanthus spreading?

Install a 600mm vertical root barrier of galvanised steel or pond liner around the plant at planting time. Lift and divide the crown every four years and pot up any roots wandering outside the barrier. Glyphosate kills regrowth but root fragments below 200mm often survive a single application.

Why is my acanthus not flowering?

The most common cause is the plant being under three years old or growing in too much shade. Other causes are recent root disturbance, late spring slug damage to the central crown, or planting in shallow soil under 300mm deep. Acanthus needs a settled root run and a full summer to set flower buds.

How do you propagate acanthus?

Take 75mm root cuttings from November to February. Lift a section of root with a fork, cut into pencil-thick lengths, and push vertically into gritty compost with the top flush to the surface. Keep cool and moist. Cuttings root in 8-10 weeks and produce flowering plants in their third year. For more on the Greek architectural use of the leaves see the Royal Horticultural Society acanthus profile.

Now you’ve mastered acanthus

Now you’ve mastered the architectural side of the border, read our guide to the best perennial plants for UK gardens for the next step in building a long-season scheme. If you are pairing acanthus with grasses for a prairie look, the Miscanthus sinensis growing guide is also worth a read.