Bistorta milletii

RHS Plant Profile

crimson knotweed

RHS

Synonyms

Polygonum milletii
Persicaria milletii

Bogs Herbaceous Perennial

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A clump-forming, upright, semi-evergreen perennial with linear to lance-shaped, pointed, dark green leaves to 30cm long with prominent mid-ribs. Profuse, dense, cylindrical spikes of slender, rich-crimson flowers from early summer to late autumn to 60cm tall

Position

Full sun, Partial shade

Soil Types

Clay, Loam

Max Height

0.5-1 metres

Max Spread

0.1-0.5 metres

Size

Time to Maturity: 2–5 years
Max Spread: 0.1-0.5 metres
Max Height: 0.5-1 metres

Growing Conditions

Clay Loam

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

Position

Full sun Partial shade

Aspect: South–facing or North–facing or East–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): H3

Colour & Scent

Season	Stem	Flower	Foliage	Fruit
Spring
Summer
Autumn
Winter

Botanical Details

Family: Polygonaceae
Native to GB/Ireland: No
Foliage: Semi evergreen
Habit: Bushy
Genus: A genus of herbaceous, rhizomatous perennials with erect, unbranched stems, bearing short terminal spikes of small, white or pink, bell-shaped flowers
Name Status: Correct
Plant Range: Himalaya to C China

How to Grow

Cultivation

Grow in any moist soil in full sun or partial shade. Tough and non-invasive but may self-seed

Propagation

Propagate by division in spring or autumn

Suggested planting locations and garden types

City and courtyard gardens
Gravel garden
Cottage and informal garden
Wildflower meadow
Flower borders and beds

Pruning

Cut back after flowering

Pests

Generally pest-free

Diseases

Generally disease-free