Polygonum bistorta 'Superbum' (Knotweed) — Mat-forming, clump-forming or tall and upright

Overview

Polygonum bistorta 'Superbum' is a mat-forming, clump-forming or tall and upright perennial in the genus Polygonum, part of the Polygonaceae family, with deciduous; simple, lance-shaped to heart-shaped, often marked or autumn-tinted foliage. It typically grows around 0.5 m tall. Polygonum bistorta 'Superbum' grows best in full sun to partial shade, and tolerates almost any soil and including heavy clay soils and acid and neutral or alkaline pH. Its UK hardiness is rated H5-H7. Suggested uses include borders, cottage gardens and naturalistic plantings. It is native to Europe.

About

Polygonum bistorta 'Superbum' is a perennial in the family Polygonaceae that flowers from July to September. It reaches about 0.5 m and can form mats, clumps or produce taller, upright flowering stems. Leaves are deciduous, simple and range from lance-shaped to heart-shaped and may take autumn tints. It suits full sun to partial shade and tolerates almost any soil, including heavy clay, provided it is not allowed to dry out.

Wikipedia contributors, CC BY-SA 4.0 — Bistorta officinalis

About the genus

Polygonum is a genus of about 130 species of flowering plants in the buckwheat and knotweed family Polygonaceae. Common names include knotweed and knotgrass. In the Middle English glossary of herbs Alphita, it was known as ars-smerte.

Wikipedia contributors, "Polygonum", CC BY-SA 4.0 — Polygonum

In the garden

Polygonum bistorta 'Superbum' is a European perennial in the Polygonaceae, grown for its summer display and its adaptable habit, which ranges from mat-forming to clump-forming or more erect stems. Plants produce a basal rosette of simple, lance- to heart-shaped leaves and send up flowering stems that appear in the summer months; flowering occurs from July to September. Mature clumps typically reach around 0.5 m in height. Plant it where the soil stays moist rather than dry: the species tolerates a wide range of pH (acid, neutral or alkaline) and will grow in almost any soil, including heavy clay. It prefers full sun to partial shade and will tolerate both exposed and sheltered sites, making it straightforward to place across a garden. Hardiness is H5–H7 (hardy to fully hardy), so it survives normal UK winters in outdoor planting. Use Polygonum bistorta 'Superbum' in mixed borders, cottage gardens or naturalistic schemes where damp ground is available; it fills low ground between taller perennials and can form a neat clump or spread as a low mat. Position it behind lower plants so the flowering stems, which rise to about 0.5 m from July to September, sit clearly above the basal leaves.

Growing conditions

Best soil and position for Polygonum

Sunlight: Full sun to partial shade
Soil type: Almost any soil, including heavy clay
Soil pH: Acid, neutral or alkaline
Soil moisture: Moist; most tolerate damp ground and dislike drought
Aspect: Any
Exposure: Exposed or sheltered
UK hardiness: H5-H7

Plant details

Polygonum bistorta 'Superbum' size, habit and characteristics

Plant type: Perennial
Habit: Mat-forming, clump-forming or tall and upright
Foliage: Deciduous; simple, lance-shaped to heart-shaped, often marked or autumn-tinted
Height: 0.5 m
Suggested uses: Borders, cottage gardens, naturalistic plantings
Native to: Europe

Care notes

Pruning and caring for Polygonum bistorta 'Superbum'

Cultivation: Undemanding to the point of needing restraint rather than encouragement. Give reliable moisture and they flower for months. Vigour is the main consideration: check the spread of any given species before planting, since the running kinds colonise fast and are difficult to remove once established, while the clump-forming ones are well behaved. Note that most garden knotweeds are now classified under Persicaria.
Pruning: Cut back to the base in late autumn, or leave the dried spikes standing for winter interest and clear in early spring. Shear mat-forming kinds after the first flush to tidy them.
Propagation: Divide in spring or autumn - most divide very easily. Basal cuttings root readily in spring.
Pest resistance: Slugs graze new growth; otherwise notably trouble-free.
Disease resistance: Healthy and robust. Powdery mildew occurs on plants that dry out.

Frequently asked questions

How do I grow Polygonum bistorta 'Superbum'?

Undemanding to the point of needing restraint rather than encouragement. Give reliable moisture and they flower for months. Vigour is the main consideration: check the spread of any given species before planting, since the running kinds colonise fast and are difficult to remove once established, while the clump-forming ones are well behaved. Note that most garden knotweeds are now classified under Persicaria.

Where is the best place to plant Polygonum bistorta 'Superbum'?

Polygonum bistorta 'Superbum' prefers full sun to partial shade. It suits exposed or sheltered positions.

What soil does Polygonum bistorta 'Superbum' need?

Polygonum bistorta 'Superbum' grows best in almost any soil and including heavy clay soil. It prefers acid and neutral or alkaline soil. Aim for soil that stays moist; most tolerate damp ground and dislike drought.

How do I prune Polygonum bistorta 'Superbum'?

Cut back to the base in late autumn, or leave the dried spikes standing for winter interest and clear in early spring. Shear mat-forming kinds after the first flush to tidy them.

How big does Polygonum bistorta 'Superbum' grow?

Polygonum bistorta 'Superbum' reaches a height of 0.5 m.

Is Polygonum bistorta 'Superbum' hardy in the UK?

Polygonum bistorta 'Superbum' has an RHS hardiness rating of H5, meaning it is hardy in most of the UK, tolerating -15 to -10°C.

How do I propagate Polygonum bistorta 'Superbum'?

Divide in spring or autumn - most divide very easily. Basal cuttings root readily in spring.

More in the Polygonum genus

Browse all Polygonum →