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Justicia americana

American water-willow

Acanthaceae Eastern and central North America

Attracts Pollinators Attracts Butterflies Container Friendly

Native to North America

SunFull Sun – Part Shade

WaterHigh

HardinessZones 4–9

Overview

Justicia americana is an emergent aquatic perennial in the Acanthaceae, growing 1-3 feet (30-90 cm) tall and spreading by rhizomes to form dense colonies in shallow water and along shorelines. The narrow, lance-shaped leaves are 3-6 inches (8-15 cm) long, opposite, and willow-like, giving the plant its common name. From late spring through summer it bears slender stalks topped with small two-lipped flowers about 0.5 inch (12 mm) long, white to pale lavender with purple streaks and spots on the lower lip. The flowers attract bees and other insects, and the underwater stems and roots shelter small fish, insect larvae, and amphibians. It roots in mud at the water edge or in water up to about 3 feet (90 cm) deep, occurring along streams, rivers, ponds, and lakes across eastern and central North America. The spreading rhizomes bind sediment and reduce shoreline erosion, but the same growth lets colonies expand widely and crowd small or still waters. Plants die back to the rhizome in winter and are intolerant of drying out, declining quickly where water levels drop for long periods.

Native Range

Native to eastern and central North America, from Ontario and Quebec south to Texas and Georgia. It grows in shallow water and on muddy margins of streams, rivers, ponds, and lakes.

Suggested Uses

Justicia americana is used along pond and stream margins, in water gardens, and in shoreline restoration and erosion control. It shelters fish, frogs, and aquatic insects in naturalized water features. Its spreading habit suits large ponds and banks rather than small contained pools.

How to Identify

Look for dense, colonial stands of erect stems standing in shallow water, with opposite, narrow, willow-like leaves. The small two-lipped flowers are white to pale lavender with purple markings on the lower lip, held on slender stalks above the water. The colonial habit and aquatic setting distinguish it from true willows.

Appearance

Size & Dimensions

Height1' - 3'

Width/Spread2' - 4'

Colors

Flower Colors

white

purple

Foliage Colors

green

Bloom Information

Bloom Period

~16 weeks

Spring Summer

Small white-and-purple flowers open from late spring through summer, roughly May to September. Bloom continues over many weeks as new stalks form. The flowers are followed by small capsules that eject their seeds.

Detailed Descriptions

Flower Description

white with purple markings

Foliage Description

green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 4-12 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 Range6.0 - 8.0(Neutral)

357912

Soil Types

clay loam silt

Drainagewet

Water & Climate

Water Needs

High

Frost Tolerance

hardy

Time to Maturity

2-3 years

Care & Maintenance

Care Guide

Justicia americana grows in full sun to part shade in shallow standing water or on permanently wet, mucky soil along shorelines. It needs constant moisture and does not survive in soil that dries out. Planted in mud at the water edge or in submerged containers, it spreads steadily by rhizome to form colonies. It tolerates moving water and periodic flooding and helps stabilize banks. Propagation is by division of the rhizome or by stem cuttings rooted in wet soil. In small ponds its spread may need to be contained.

Pruning

No routine pruning is required. Spreading colonies can be thinned by pulling or cutting rhizomes in spring to keep the planting within bounds.

Container Growing

✓ Suitable for container growing

Minimum container size: 3 gallons

✓ Toxicity

Non-toxic