Acanthus spinosus Spinosissimus Group

RHS Plant Profile

spiny bear's breech Spinosissimus Group

Synonyms

Acanthus spinosus var. spinosissimus
Acanthus spinosus misapplied
Acanthus spinosissimus

Herbaceous Perennial

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A group of clump-forming perennials, with finely cut, spiny, deep grey-green basal leaves with white midribs. Tall, spiny spikes of white flowers with purple hoods are produced in summer. This group is named for its spiny foliage, and may not flower as prolifically as some other cultivars

Position

Full sun, Partial shade

Soil Types

Chalk, Clay, Loam, Sand

Max Height

1-1.5 metres

Max Spread

0.5-1 metres

Size

Time to Maturity: 2–5 years
Max Spread: 0.5-1 metres
Max Height: 1-1.5 metres

Growing Conditions

Chalk Clay Loam Sand

Moisture: Moist but well–drained or Well–drained
pH: Acid or Alkaline or Neutral

Position

Full sun Partial shade

Aspect: East–facing or North–facing or South–facing or West–facing
Exposure: Exposed or Sheltered
Hardiness

Hardiness Ratings

All ratings refer to the UK growing conditions unless otherwise stated. Minimum temperature ranges (in degrees C) are shown in brackets

H1A: under glass all year (>15C)
H1B: can be grown outside in the summer (10 - 15)
H1C: can be grown outside in the summer (5 - 10)
H2: tolerant of low temperatures, but not surviving being frozen (1 to 5)
H3: hardy in coastal and relatively mild parts of the UK (-5 to 1)
H4: hardy through most of the UK (-10 to -5)
H5: hardy in most places throughout the UK even in severe winters (-15 to -10)
H6: hardy in all of UK and northern Europe (-20 to -15)
H7: hardy in the severest European continental climates (< -20): H5

Colour & Scent

Season	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family: Acanthaceae
Native to GB/Ireland: No
Foliage: Deciduous, Semi evergreen
Habit: Clump forming
Genus: Acanthus are robust herbaceous perennials with handsome, lobed foliage and tall, erect racemes of two-lipped flowers with colourful bracts
Name Status: Accepted

How to Grow

Cultivation

Grow in sun or part shade, will tolerate most soils but thrives in deep loam. Acanthus need careful positioning as they can be difficult to remove once established. Has the potential to become a nuisance if not managed well

Propagation

Propagate by division or by root cuttings

Suggested planting locations and garden types

Cottage and informal garden
Flower borders and beds

Pruning

Cut down old flower stems

Pests

Generally pest-free

Diseases

May be susceptible to powdery mildews