Amphibious bistort

Amphibious bistort: how do you recognise it?

Habit

Creeping rhizome with long floating or trailing stems that cover 1 m or more; only 10 cm tall above the water.

Leaves

In water oblong-oval, 5–15 cm, glossy and smooth, floating on long stalks; on land narrower, shorter-stalked and slightly hairy.

Flowers

Dense, cylindrical spikes of 2–4 cm made up of small pink flowers, from June to September.

Roots

Vigorous rhizome; the stems also root at the nodes, so it spreads quickly.

Pond zone

From the wet bank and marsh zone to deep water, down to about 1 m below the surface.

Flowering: June–September · Plants: April–June · Pruning: July–August and October

Why grow it?

• Grows both in water up to 1 m deep and on a wet bank: one plant for two pond zones.
• Pink flower spikes from June to September, a long season for a native water plant.
• The flowers attract bees, hoverflies and other insects.
• The floating leaves cast shade, which holds back algae and gives shelter to tadpoles and small pond creatures.
• Damselflies and dragonflies like to rest on the floating leaves.
• Native and fully hardy: a reliable choice for a wildlife pond.

Amphibious bistort: where does it grow best?

• Full sun gives the best flowering; in shade it grows more slowly and flowers little.
• Still or slow-moving water in a pond or pool, or a wet bank that hardly ever dries out.
• Water depth: ideally 20–50 cm above the basket, but it tolerates about 1 m. On the bank it grows in wet loam, clay or peaty soil.
• Not fussy: acid, neutral and alkaline water all suit it.
• Allow about 1 m² of water surface per plant; in a small pond one plant in a basket is enough.

Light

Sun

Soil type

Loam, clay or peat

Acidity

Not fussy

Moisture

Wet

Size

0.1 m tall, 1 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Water lily: Larger floating leaves and flowers in deep water; together they cover the water, so leave enough open water.
• Yellow flag: Upright sword-shaped leaves and yellow flowers in May–June, before the bistort flowers.
• Purple loosestrife: Purple spikes on the bank in the same summer months, also excellent for bees.
• Water mint: Scented leaves and lilac flowers in the shallow margin.
• Rigid hornwort: A submerged oxygenator that helps keep the water clear.

Amphibious bistort: when and how to plant it?

Plant in April–June.

1. Plant from April to June, when the water warms up and the plant is in active growth.
2. Use an aquatic basket of at least 10 litres filled with heavy garden soil or clay, without potting compost or fertiliser: they feed the algae.
3. Lay the rhizome just below the soil surface and top with 2–3 cm of gravel, so the soil does not wash out and fish do not dig in it.
4. Stand the basket at 10–20 cm depth first and lower it after a few weeks to 20–50 cm below the water surface.
5. On a wet bank, plant straight into the mud, about 1 m from other plants. Water in and keep the soil wet until it has established.

Care

Water

Not needed in the pond. On the bank the soil must stay wet; in dry summers top up the pond with rainwater.

Feeding

Do not feed: extra nutrients in a pond mainly feed algae.

Keeping in check

In summer, cut or pull out stems that spread too far, so there is open water for other plants and wildlife.

Tidying

In autumn, take dying leaves out of the water so they do not rot on the bottom.

Dividing

Every 2–3 years, when the basket is full of roots, divide the plant in spring.

Tip: Lower the basket in stages: start at 10–20 cm deep and move it deeper as the stems grow longer. That way the young leaves reach the light straight away.

Amphibious bistort: when to prune it?

Pruning months: July–August and October.

When: Real pruning is not needed. In July–August shorten stems that spread too far, and in October remove the dying leaves.

How:

• Cut overlong stems off at the edge of the basket, or gently pull them out with their roots.
• Leave enough floating leaves: plants covering a third to half of the water surface is good for a healthy pond.
• In October remove yellow and brown leaves with a pond rake or scissors, without pulling up the rhizome.
• Leave whatever you take out of the water on the bank for a day, so small creatures can crawl back into the pond.

Caution: It grows fast and roots wherever a stem touches the bottom: in a small pond always plant it in a basket.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Cuttings

From May to August, cut a 15–20 cm piece of stem with a few nodes and lay it in a basket of wet soil or in shallow water. Roots soon form at the nodes.

Division

In April–May, take the rhizome out of the basket, cut it into pieces with a few nodes each and plant each piece in its own basket.

Amphibious bistort: how does it get through the winter?

Hardy to −30 °C.

• Fully hardy, to about −30 °C: no protection is needed in a Belgian pond.
• The floating leaves die back in autumn; the rhizome overwinters in the mud on the bottom.
• Plants on the bank also come through winter without care, as long as the soil does not dry out.
• During long frosts keep a hole open in the ice of a pond with fish, without hitting the ice.

Diseases and pests

• Spreading too much: The floating leaves cover almost the whole pond. Shorten the stems and divide the basket every few years.
• Aphids: Small black aphids on floating leaves and flower spikes in summer. Hose them off into the water: fish and pond creatures eat them. Never use pesticides in or near a pond.
• Few flowers: Too much shade or a young plant. A sunny spot helps; the land form on the bank often flowers less than the floating form.
• Holes in the leaves: Small beetles and their larvae eat holes in the floating leaves. Usually harmless; cut off badly damaged leaves.

Through the year

• April: Plant or divide into an aquatic basket. The first floating leaves appear.
• May: Plant. Take cuttings from young stems.
• June: First pink flower spikes. Planting is still possible.
• July: In flower. Shorten stems that spread too far.
• August: In flower. Shorten stems. Top up the pond with rainwater in dry spells.
• September: Last flowers. Bees and hoverflies on the spikes.
• October: Take dying leaves out of the water.
• November: Dormant. The rhizome overwinters on the bottom.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• Amphibious bistort changes its looks depending on whether it grows in water or on land: floating with smooth, glossy leaves, or upright with narrower, hairy leaves.
• The species name amphibia refers to this life in two worlds, just like an amphibian.
• The genus name Persicaria comes from the Latin persica, peach, after the leaf shape of some species.