Polygonum amplexicaule oxyphyllum of gardens (Knotweed) — Mat-forming, clump-forming or tall and upright

Overview

Polygonum amplexicaule oxyphyllum of gardens 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 1.2 metres tall. Polygonum amplexicaule oxyphyllum of gardens 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 China, Himalayas and Pakistan.

About

Polygonum amplexicaule oxyphyllum of gardens is a moisture-preferring perennial in the Polygonaceae that can grow as a mat, a clump or a tall, upright plant. Leaves are simple, lance-shaped to heart-shaped, deciduous and often marked or autumn-tinted. It reaches about 1.2 metres and carries summer flower spikes from July to September. Plants suit full sun to partial shade and tolerate almost any soil, including heavy clay, provided the site is not dry.

Wikipedia contributors, CC BY-SA 4.0 — Bistorta amplexicaulis

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

This Polygonum originates from China, the Himalayas and Pakistan and sits in the buckwheat family, Polygonaceae. Growth habit is variable: some plants spread low and mat-forming, others make clumps or rise to a tall, architectural 1.2 metres. The foliage dies back for winter and may show markings or autumn tints before leaf fall. Give it full sun to partial shade and avoid drought-prone spots — the species prefers a reliably moist root run. It will tolerate heavy clay and a wide pH range (acid, neutral or alkaline). Aspect and exposure are flexible: it performs equally well in exposed or sheltered sites. Hardiness is H5–H7, which means the plant is hardy in most UK gardens through to fully hardy areas. Where it works best is dictated by its moisture preference and variable habit. Use taller forms towards the rear of mixed borders or in naturalistic, moisture-retentive schemes; lower, mat-forming types can be used where ground cover is required on heavy soils. Expect a succession of flower spikes from July to September that extend interest through summer into early autumn.

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 amplexicaule oxyphyllum of gardens 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: 1.2 metres
Native to: China, Himalayas, Pakistan

Care notes

Pruning and caring for Polygonum amplexicaule oxyphyllum of gardens

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 amplexicaule oxyphyllum of gardens?

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 amplexicaule oxyphyllum of gardens?

Polygonum amplexicaule oxyphyllum of gardens prefers full sun to partial shade. It suits exposed or sheltered positions.

What soil does Polygonum amplexicaule oxyphyllum of gardens need?

Polygonum amplexicaule oxyphyllum of gardens 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 amplexicaule oxyphyllum of gardens?

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 amplexicaule oxyphyllum of gardens grow?

Polygonum amplexicaule oxyphyllum of gardens reaches a height of 1.2 metres.

Is Polygonum amplexicaule oxyphyllum of gardens hardy in the UK?

Polygonum amplexicaule oxyphyllum of gardens 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 amplexicaule oxyphyllum of gardens?

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

More in the Polygonum genus

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