Red bistort

Sun

Full sun to partial shade; afternoon shade is useful in hot climates.

Water

Keep the soil consistently moist, particularly during establishment and summer heat. Established clumps tolerate brief dry spells, but prolonged drought reduces flowering and damages foliage.

Soil

Moist, humus-rich soil with reasonable drainage; tolerates clay and a broad range of soil pH. Avoid very dry ground and prolonged stagnant water.

Height

3-4 ft (0.9-1.2 m)

Spread

2-4 ft (0.6-1.2 m)

Flowers

Summer to autumn; slender spikes of red to reddish-pink flowers. Named cultivars also offer pink or white flowers.

Foliage

Broad, pointed green leaves form a dense mound; upper leaves clasp the stems. Foliage dies back in winter.

Growth

Moderate to fast once established.

Care needed

Low

• Water newly planted clumps regularly through their first growing season.
• Water established plants deeply during extended dry weather rather than letting the root zone dry out completely.
• Apply 2 in (5 cm) of compost or leaf mould in spring, keeping it clear of emerging shoots.
• Avoid heavy feeding; a spring compost mulch is usually sufficient.
• Divide congested clumps in spring if flowering declines or they outgrow their space.

Pruning. Cut dead stems to ground level in late winter or early spring before new growth develops. Remove spent flower spikes during the growing season if you want a tidier appearance, though routine deadheading is not essential.

Late winter

Cut down last year's stems before fresh shoots emerge.

Spring

Plant or divide clumps, water thoroughly and apply a compost mulch.

Late spring

Check moisture around new plants and watch young shoots for slug or snail damage.

Summer

Water during dry spells and remove damaged leaves or spent spikes if needed.

Autumn

Leave healthy stems standing for structure, or cut them back once completely dead if they collapse onto neighbouring plants.

• Plant repeated groups through a deep border to carry flower colour from summer into autumn.
• Combine with ornamental grasses for upright flower spikes above a softer, moving background.
• Use beside a pond or stream where the soil stays moist, but keep the crown out of standing water.
• Pair with broad-leaved shade perennials at a bright woodland edge for contrasting leaf shapes.

Garden styles it suits: New perennial (prairie), Cottage garden, English country, Wildlife garden, Pollinator garden and Woodland.

Plant it with: Japanese anemones, Joe-Pye weed, Tufted hair grass, Siberian iris, Hostas and Meadowsweet.

Wildlife: The flowers provide nectar and pollen for bees and other visiting insects over a long flowering season.

• Slugs and snails may damage young shoots: inspect emerging growth and use hand removal or a locally approved iron-phosphate bait if necessary.
• Drought can cause wilting, scorched leaves and fewer flowers: water deeply and mulch to conserve moisture.
• Powdery mildew may develop in dry, crowded conditions: maintain soil moisture, improve airflow and remove badly affected foliage.
• Large clumps can crowd smaller neighbours: lift and divide the outer sections in spring.

Not known to be toxic to cats, dogs, horses or people. No particular part is recognised as poisonous, but species-specific toxicity information is limited; do not treat it as an edible plant.

• Common bistort (Bistorta officinalis)

  Usually flowers earlier, in late spring or early summer, with shorter, denser, pale-pink flower spikes rather than the slender red spikes typical of red bistort.

• Lesser knotweed (Bistorta affinis)

  Forms a low, spreading carpet with much smaller leaves and short pink flower spikes, rather than a tall, upright clump.

Persicaria refers to leaves resembling those of peach, while amplexicaulis means stem-clasping, describing the way the upper leaves wrap around the stems.

Propagation. Divide established clumps in spring, replanting rooted sections promptly and watering them well. Seed can be sown in autumn, but seedlings may differ from the parent; divide named cultivars to keep their characteristics.

Accepted botanical name

Bistorta amplexicaulis Persicaria amplexicaulis is an older name for Bistorta amplexicaulis.

Native range

Afghanistan, China North-Central, China South-Central, China Southeast, East Himalaya, Nepal, Pakistan and West Himalaya.

Sources: GBIF (CC BY 4.0) and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.