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Persicaria decipiens

slender knotweed

Polygonaceae Australia and Africa

Attracts Pollinators Attracts Butterflies Container Friendly

SunFull Sun – Part Shade

WaterHigh

HardinessZones 8–10

Overview

Persicaria decipiens, the slender knotweed, is a sprawling to upright perennial herb in the family Polygonaceae found in wetlands across Australia and parts of Africa. The reddish, jointed stems are 12-36 inches (30-90 cm) long, swollen at the nodes where a papery sheath wraps the stem, and root where they touch wet ground. The narrow, lance-shaped leaves are 2-6 inches (5-15 cm) long and often carry a dark central blotch. Slender spikes of tiny pink to white flowers, each spike 1-2 inches (2.5-5 cm) long, appear over much of the year at the stem tips. Small dark nutlets follow and are taken by waterbirds. The species grows on the margins of swamps, dams, creeks, and slow drains, in mud and shallow water, and spreads by rooting stems to form patches. It needs constantly moist to wet soil and declines where the ground dries out. The fast, rooting growth can crowd small marginal plants at pond edges.

Native Range

Persicaria decipiens is native to Australia, where it occurs in all states, and to parts of Africa. It grows on the margins of swamps, lagoons, dams, creeks, and drainage lines, in wet mud and shallow standing water.

Suggested Uses

Grown at pond and dam margins, in bog gardens, and in wetland restoration for bank stability and waterbird food. Suited to constantly wet edges and rain gardens that hold moisture. Spaced 12-18 inches (30-45 cm) apart along a wet margin.

How to Identify

Recognised by reddish jointed stems with a papery sheath at each swollen node and narrow lance-shaped leaves that often bear a dark central blotch. Slender spikes of tiny pink to white flowers sit at the stem tips over much of the year. The wetland habit, node sheaths, and blotched leaves separate it from related knotweeds.

Appearance

Size & Dimensions

Height1' - 3'

Width/Spread1' - 3'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~24 weeks

Spring Summer Fall

Flowering extends over much of the year, mainly September to March, with slender pink to white flower spikes at the stem tips. The small flowers draw native bees, butterflies, and other insects. Dark seeds ripen along the spikes and are eaten by waterbirds.

Detailed Descriptions

Flower Description

pink to white

Foliage Description

green, often with dark central blotch

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 5-10 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range5.5 - 7.5(Neutral)

357912

Soil Types

clay loam silt

Drainagewet

Water & Climate

Water Needs

High

Frost Tolerance

hardy

Time to Maturity

1 year

Care & Maintenance

Care Guide

Grows in full sun to part shade on constantly moist to wet clay, loam, or silt soils, including shallow standing water at pond and dam margins. The plant needs reliable moisture and declines quickly where the soil dries out. Rooting stems spread it along wet edges, so it fills marginal ground and may crowd smaller plants. Frost cuts back top growth, which reshoots from the base and rooted nodes in spring. It needs no feeding in fertile wet soils. Cutting back spreading stems keeps it within bounds at pond edges.

Pruning

Cutting back straggly or spreading stems through the growing season keeps the patch contained at water margins. Stems that root beyond the intended area can be pulled at any time. No structural pruning is needed.

Pruning Schedule

summerfall