Helleborus × sternii Blackthorn Group

RHS Plant Profile

hellebore Blackthorn Group

RHS 2000

Synonyms

Helleborus × sternii 'Blackthorn Strain'

Herbaceous Perennial

Blackthorn Group are evergreen perennials to 45cm with purplish biennial stems bearing leaves composed of three bluish-green, pale-veined leaflets. Nodding, pale pinkish-green flowers 3-5cm in width are borne in open clusters

Position

Full sun, Partial shade

Soil Types

Chalk, Clay, Loam

Max Height

0.1-0.5 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity: 2–5 years
Max Spread: 0.1-0.5 metres
Max Height: 0.1-0.5 metres

Growing Conditions

Chalk Clay Loam

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

Position

Full sun Partial shade

Aspect: East–facing or South–facing or North–facing or West–facing
Exposure: 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): H4

Colour & Scent

Season	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family: Ranunculaceae
Native to GB/Ireland: No
Foliage: Evergreen
Habit: Clump forming
Potentially harmful: Harmful if eatenskin irritant. Wear gloves and other protective equipment when handling. Pets: Harmful if eatenskin irritant. For further information and contact numbers regarding pets, see the HTA guide to potentially harmful plants
Genus: Helleborus can be rhizomatous, herbaceous or semi-evergreen perennials forming a clump of pedate basal leaves, or evergreen with erect, leafy stems. Large, bowl-shaped flowers are borne in loose clusters in late winter or spring
Name Status: Accepted

How to Grow

Cultivation

Thrives in neutral to alkaline soils that are moist, fertile and humus-rich. Partial shade is ideal but can tolerate full sun. Provide shelter from strong, cold winds. Mulch annually in autumn

Propagation

Propagate by seed in pots in a cold frame as soon as seed is ripe or propagate by division after flowering in early spring or late summer. Named cultivars do not come true from seed

Suggested planting locations and garden types

Cottage and informal garden
Wildlife gardens
Cut flowers
Flower borders and beds
Underplanting of roses and shrubs

Pruning

Remove faded or damaged foliage as the flowers appear

Pests

May be susceptible to hellebore aphid, hellebore leaf miner and snails

Diseases

May be susceptible to hellebore leaf spot and hellebore black death