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

Overview

Polygonum cuspidatum compactum 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. Polygonum cuspidatum compactum 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.

About

Polygonum cuspidatum compactum of gardens is a perennial in the knotweed family with a variable habit that can form mats, clumps or grow more erect. It has deciduous, simple leaves that range from lance-shaped to heart-shaped and are often marked or take on autumn tints. Plants suit full sun to partial shade and prefer reliably moist soil, tolerating heavy clay and a wide pH range. Flowering occurs in the UK from July to September.

Wikipedia contributors, CC BY-SA 4.0 — Reynoutria japonica

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 cuspidatum compactum of gardens belongs to the Polygonaceae and shows a range of growth forms from low, mat-forming patches to clump-forming or taller, upright stems. The foliage is deciduous and often marked, with leaves that can take on autumn colours as the season ends. Flowers appear in the UK between July and September. Position it in full sun to partial shade and do not expect it to need specialist soil: it grows in almost any soil type, including heavy clay, and tolerates acid, neutral or alkaline conditions. It prefers moist ground and most plants will struggle if left to dry out; plant in a spot where soil moisture is consistent or where irrigation can be provided during dry spells. Aspect can be any and it tolerates both exposed and sheltered sites. Hardiness ranges H5–H7, so it tolerates most UK winter conditions. Use it where a variable habit is acceptable — in informal mixed borders, moisture-retentive beds or larger-scale plantings where its clump-forming tendency fits. Take into account its seasonal leaf loss and the tendency for foliage to develop autumn tints before dropping.

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 cuspidatum compactum 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

Care notes

Pruning and caring for Polygonum cuspidatum compactum 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 cuspidatum compactum 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 cuspidatum compactum of gardens?

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

What soil does Polygonum cuspidatum compactum of gardens need?

Polygonum cuspidatum compactum 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 cuspidatum compactum 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.

Is Polygonum cuspidatum compactum of gardens hardy in the UK?

Polygonum cuspidatum compactum 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 cuspidatum compactum of gardens?

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

More in the Polygonum genus

Browse all Polygonum →