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Persicaria spp.

knotweeds, smartweeds, and waterpeppers

Polygonaceae

Worldwide, most diverse in temperate and warm regions across all continents

Attracts Pollinators Attracts Butterflies Deer Resistant Container Friendly

Native to North America

SunFull Sun – Part Shade

WaterMedium

HardinessZones 4–9

Overview

Persicaria spp. is a genus of about 100 species of annual and perennial herbs in the Polygonaceae family, found on every continent and most common in damp ground, ditches, pond margins, and meadows. The genus, which includes the knotweeds, smartweeds, and waterpeppers, was once placed in Polygonum spp. and shares the family's swollen stem joints wrapped in a papery sheath (ocrea). Leaves are usually lance-shaped, 2-10 inches (5-25 cm) long, and many carry a dark chevron or blotch in the center. Tiny flowers, white through pink to red, crowd into slender spikes or rounded heads from summer into fall on stems 6 to 72 inches (15 to 180 cm) tall. Ornamental species such as P. amplexicaulis are grown in borders for their long bloom, while P. maculosa and others self-seed into common garden and field weeds. Several species spread by creeping rhizomes and can crowd out neighbors in moist soil. The genus draws bees and other pollinators, and its seeds feed birds and waterfowl. Mile-a-minute weed (P. perfoliata), an aggressive annual vine, is a regulated invasive species in parts of North America.

Native Range

Persicaria spp. occurs worldwide, with species native to North America, Europe, Asia, Africa, and beyond. North American natives include P. amphibia, P. pensylvanica, and P. virginiana, while P. maculosa and P. perfoliata are naturalized or invasive introductions.

Suggested Uses

Ornamental species are grown in borders, rain gardens, and pond-side plantings for long summer-to-fall bloom. Native smartweeds are used in wetland restoration and wildlife plantings, where seeds feed birds and waterfowl. The flowers draw bees and butterflies.

How to Identify

Identify Persicaria spp. by swollen stem nodes sheathed in a papery ocrea and lance-shaped leaves that often bear a dark V-shaped blotch. Small flowers without true petals crowd into dense, often nodding spikes in white, pink, or red. The peppery taste of waterpepper leaves and the chevron leaf mark help separate the smartweeds from related genera. Ripe seeds are small, shiny, and three-sided or lens-shaped.

Appearance

Size & Dimensions

Height6" - 6'

Width/Spread1' - 4'

Reaches mature size in approximately 2 years

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~12 weeks

Summer Fall

Bloom runs from summer into fall, generally June through October, with ornamental species flowering for many weeks. The small flowers open along slender spikes from the base upward and are visited by bees, flies, and butterflies. Cooler fall weather often deepens the pink and red tones. Seeds ripen and drop through fall.

Detailed Descriptions

Flower Description

pink to white

Foliage Description

green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 4-8 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

Drainagemoist

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

flowers in the first or second season

Care & Maintenance

Care Guide

Plants in this genus grow in full sun to part shade and prefer moist, fertile soil across pH 5.5-7.5, with several species thriving at pond edges and in seasonally wet ground. They tolerate clay and standing water that many perennials cannot, but most decline in hot, dry sites. Rhizomatous species spread steadily and may need a barrier or division to stay in bounds, while annual species rely on heavy self-seeding. Cutting back spent stems limits unwanted seedlings. Few pests are serious, though leaf beetles and rust appear on some species. Hardiness spans USDA zones 4-9 depending on species.

Pruning

Cutting perennial species to the ground in late fall or early spring clears the dead stems before new growth. Shearing after the first bloom can prompt a fresh flush and reduce self-seeding. Removing flower spikes before the seeds ripen limits spread in weedy species.