Red bistort

Persicaria amplexicaulis

In other languages: Duizendknoop (Nederlands) · Renouée amplexicaule (Français)

Red bistort is a robust perennial from the Himalaya, where it grows in moist mountain meadows and woodland edges. It forms a broad, dense clump with large, pointed leaves and flowers from July until the first frost with countless narrow, red spikes held above the foliage. Gardeners value it for its long, reliable flowering, its low maintenance and the way it suits naturalistic borders. Well-known cultivars are the bright red ‘Firetail’ and the white ‘Alba’; pink forms also exist.

Updated on 9 October 2026

Light
Sun or partial shade
preferably some sun
Moisture
Normal to wet
must not dry out
Legal basis
Loam, clay or peat
any pH
Hardiness
Fully hardy
down to -25 °C
Size
1 m
tall, 1 m wide
Flowering
July–October

Key facts
Pruning months	March
Height	1 m
Native to Belgium	No, planted
Good for bees, butterflies and birds	Yes, for bees and butterflies
Poisonous to people and pets	Not known to be poisonous
Flowering	July–October

Identify

Red bistort: how do you recognise it?

Habit: Broad, dense clump 1–1.2 m tall and about as wide.
Leaves: Large, oval to lance-shaped with a pointed tip, 10–25 cm; the upper leaves clasp the stem.
Flower: Narrow, upright spikes of 5–15 cm made up of tiny flowers, from July until the first frost.
Colour: Red to crimson; pink and white cultivars also exist.
Roots: A sturdy, woody rootstock; the clump widens slowly without becoming invasive.

Flowering: July–October · Plants: March–May and September–October · Pruning: March

In your garden

Why grow it?

One of the longest-flowering perennials: from July until the first frost.
Bees, bumblebees and butterflies visit the spikes until late in the season.
Thrives in moist, heavy soil, where many other border plants struggle.
A sturdy plant that rarely needs staking and suffers from few diseases.
The red spikes look superb among ornamental grasses and in a natural border.

Red bistort: where does it grow best?

Sun or partial shade; full sun only if the soil stays moist.
Rich loam, clay or peaty soil; acid, neutral or chalky.
Normal to moist: it dislikes dry soil.
Plant 60–80 cm apart; after a few years one plant easily fills 1 m².

Light: Sun and partial shade
Soil type: Loam, clay or peat
Acidity: Not fussy
Moisture: Normal or wet
Size: 1 m tall, 1 m wide
Hardiness: Hardy (to -25 °C)

Goes well with

Miscanthus: Tall, swaying grass stems with the red spikes between them.
Joe Pye weed: Likes the same moist soil and flowers at the same time.
Japanese anemone: Pink or white flowers in the same late summer and partial shade.
Michaelmas daisy: Purple beside red until well into autumn.

Maintenance

Red bistort: when and how to plant it?

Plant in March–May and September–October.

Plant from March to May or in September–October, when the soil is neither frozen nor too wet.
Dig a hole twice as wide as the root ball and mix in a few spadefuls of compost.
Set the plant at the same depth as in the pot and firm the soil well.
Leave 60–80 cm between plants.
Water in thoroughly and mulch around the base with compost or leaf mould.

Care

Watering: Regularly in the first year. After that, water generously in dry summers, as drought makes the leaves droop and stops the flowering.
Feeding: In March, a layer of compost or some organic fertiliser.
Mulching: A mulch in spring keeps the soil moist in summer.
Deadheading: Not needed: it keeps producing new spikes until the frost.
Dividing: Every 4–5 years, divide large clumps or trim them back around the edge.

Tip: Water in good time in dry summers and add a layer of compost every spring: with enough moisture it flowers non-stop until the first frost.

Red bistort: when to prune it?

Pruning months: March.

When: Red bistort needs hardly any pruning. After the first frost the leaves die; cut the dead stems back to just above the ground in March.

How:

Leave the brown stems in winter as a silhouette and shelter for insects.
In March, cut all dead stems back to just above the ground, before the new shoots appear.
There is no need to remove faded spikes in summer.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division: In March–April or September–October, lift the clump and cut it with a sharp spade into pieces that each have a few buds. Replant straight away and water.
Splitting off: Without lifting the whole plant, cut a piece from the edge and replant it elsewhere.

Red bistort: how does it get through the winter?

Hardy to −25 °C.

Fully hardy, to about −25 °C: no protection needed in Belgium.
The top growth dies after the first frost; in spring the plant reshoots.
In a large pot: stand it against a wall and do not let the compost dry out.

Diseases and pests

Drought: Drooping leaves with brown edges and few new spikes. Water generously and mulch.
Slugs: They eat the young shoots in April. Pick them off in the evening or set a beer trap.
Aphids: Sometimes on the young spikes. Ladybirds usually clear them; otherwise hose them off with water.
Too big: After a few years the clump takes up a lot of room. Cut away the edge in spring or divide the plant.

Through the year

March: Cut away dead stems. Add compost. Plant or divide.
April: Planting. Mulch. Watch for slugs.
May: Planting. Water in dry spells.
June: Rapid growth. Keep the soil moist.
July: Flowering begins.
August: Full flower. Water in dry periods.
September: Flowering. Plant or divide.
October: Flowering until the first frost. Planting.
November: Foliage dies back. Leave the stems standing.
December: Rest.

Use

Good for wildlife

Bees: Nectar and pollen for honeybees and wild bees.
Butterflies: Nectar for butterflies.

You and this species

Did you know?

Unlike Japanese knotweed, it is not invasive: it forms a clump that widens only slowly.
Amplexicaulis means ‘stem-clasping’: the upper leaves wrap their base around the stem.
The genus name Persicaria comes from the Latin word for peach, as the leaves of some species resemble peach leaves.

Garden plants · All species