Polygonum amplexicaule 'Inverleith' (Knotweed) — Mat-forming, clump-forming or tall and upright

Overview

Polygonum amplexicaule 'Inverleith' 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 'Inverleith' 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 China, Himalayas and Pakistan.

About

Polygonum amplexicaule 'Inverleith' is a perennial in the Polygonaceae that can grow as mat-forming or clump-forming plants or as a taller, upright specimen, reaching about 1.2 metres. Leaves are deciduous, simple and range from lance-shaped to heart-shaped, sometimes showing markings or autumn colour. It favours moist conditions and will tolerate heavy clay while disliking drought. Flowering occurs July to September.

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

Native to China, the Himalayas and Pakistan, Polygonum amplexicaule 'Inverleith' is a perennial member of the buckwheat family that typically reaches around 1.2 metres. The foliage is deciduous and often lance- to heart-shaped; individual plants may remain low and spreading or form taller upright clumps depending on position and soil. Give it full sun to partial shade on almost any soil, including heavy clay, and keep the soil reliably moist — most plants of this type tolerate damp sites but resent drought. It grows across aspects and will perform in exposed or sheltered spots. In UK terms its hardiness ranges from H5 to H7, meaning it is hardy in most gardens through to fully hardy in colder areas. Use 'Inverleith' in mixed borders, cottage garden schemes or naturalistic plantings where late-summer flowering is desirable. Its varied habit allows it to plug gaps as a lower mat or to provide vertical structure when grown more upright. Flowering takes place July to September, so position it where spikes will be visible among summer and autumn companions.

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 'Inverleith' 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
Suggested uses: Borders, cottage gardens, naturalistic plantings
Native to: China, Himalayas, Pakistan

Care notes

Pruning and caring for Polygonum amplexicaule 'Inverleith'

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 'Inverleith'?

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 'Inverleith'?

Polygonum amplexicaule 'Inverleith' prefers full sun to partial shade. It suits exposed or sheltered positions.

What soil does Polygonum amplexicaule 'Inverleith' need?

Polygonum amplexicaule 'Inverleith' 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 'Inverleith'?

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 'Inverleith' grow?

Polygonum amplexicaule 'Inverleith' reaches a height of 1.2 metres.

Is Polygonum amplexicaule 'Inverleith' hardy in the UK?

Polygonum amplexicaule 'Inverleith' 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 'Inverleith'?

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

More in the Polygonum genus

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