Polygonum ussuriense (Knotweed) — Mat-forming, clump-forming or tall and upright

Overview

Polygonum ussuriense 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. Polygonum ussuriense 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. It is native to Northeast Asia.

About

Polygonum ussuriense is a perennial knotweed that can be mat-forming, clump-forming or grow tall and upright. Its deciduous leaves are simple, lance- to heart-shaped and are often marked or take on autumn tint. Flowering in the UK occurs from July to September. It tolerates full sun to partial shade and will grow in almost any soil, including heavy clay, provided the ground stays reasonably moist.

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 ussuriense belongs to the Polygonaceae and originates from northeast Asia. Forms vary from low, spreading mats to more erect clumps, and the leaves are deciduous — often showing markings or an autumn tint before they fall. In the UK it reliably flowers from July to September. Give this knotweed a position in full sun to partial shade and avoid sites that dry out; most examples prefer moist soil and will tolerate heavy clay. Soil pH is not a constraint — it will grow in acid, neutral or alkaline ground — and it suits any aspect. Exposure is flexible too: plants tolerate both sheltered and exposed locations. Hardiness is H5–H7, which translates to hardy through to fully hardy across most of Britain. Use the low, mat-forming types for damp patches, bank cover or where compacting heavy soil limits choices, while taller clump-forming examples sit well at the back of a naturalised or informal border. Because it prefers moisture, avoid placing it in drought-prone raised beds. Its July–September flowering period provides mid- to late-summer interest that precedes the season when leaves develop their autumn tint.

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 ussuriense 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
Native to: Northeast Asia

Care notes

Pruning and caring for Polygonum ussuriense

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 ussuriense?

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 ussuriense?

Polygonum ussuriense prefers full sun to partial shade. It suits exposed or sheltered positions.

What soil does Polygonum ussuriense need?

Polygonum ussuriense 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 ussuriense?

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.

Is Polygonum ussuriense hardy in the UK?

Polygonum ussuriense 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 ussuriense?

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

More in the Polygonum genus

Browse all Polygonum →