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

Overview

Polygonum milletii 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 milletii 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.

About

Polygonum milletii is a perennial member of the buckwheat family (Polygonaceae) that can grow as a mat-forming ground cover, clump-forming plant or as a taller upright perennial. The leaves are deciduous, simple and range from lance-shaped to heart-shaped, often showing markings or autumn tint. It flowers from July to September. It tolerates a wide range of soils, including heavy clay, and prefers moist conditions.

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 milletii sits in the genus Polygonum within the Polygonaceae and is commonly called knotweed. Habits range from mat-forming and clump-forming to more erect, upright growth, so individual plants may be used where either ground-covering or taller structure is needed. The leaves are deciduous, lance- to heart-shaped and frequently become marked or take on autumn colouring as the season progresses. Grow Polygonum milletii in full sun to partial shade on almost any soil type, including heavy clay; it will tolerate acid, neutral or alkaline pH. Plants prefer moist ground and most forms dislike drought, so a site that keeps some moisture through summer is important. It suits any aspect and will tolerate exposed or sheltered positions. Hardiness is H5–H7 (hardy to fully hardy), so it will survive typical UK winters in most garden situations. Use it where its variable habit fits the border: lower-growing clumps can fill gaps or form a mat, while taller forms provide summer height. Expect summer flowering from July to September, at which point the plant adds ephemeral seasonal interest alongside its marked foliage.

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 milletii 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

Care notes

Pruning and caring for Polygonum milletii

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 milletii?

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 milletii?

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

What soil does Polygonum milletii need?

Polygonum milletii 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 milletii?

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 milletii hardy in the UK?

Polygonum milletii 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 milletii?

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

More in the Polygonum genus

Browse all Polygonum →