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Triglochin maritima

common arrowgrass

Juncaginaceae

Northern Hemisphere coasts (Europe, Asia, North America)

Native to North America

SunFull Sun

WaterHigh

HardinessZones 3–8

Overview

Triglochin maritima is a tufted, grass-like perennial of salt marshes and coastal flats, not a true grass but a member of the arrowgrass family. It forms dense clumps of fleshy, half-cylindrical, deeply channelled leaves 4-24 inches (10-60 cm) long, rising from a short, stout rootstock with fibrous old leaf bases. From a leafless stalk it produces a slender, tapering spike of many small, stalkless green flowers, each with six tiny tepals and no showy parts. The fruits are narrow and six-sided, splitting into segments shaped like arrowheads, the feature behind the common name. It grows in the upper and middle zones of tidal salt marshes, brackish ground, and inland salt flats, rooted in salty, waterlogged, oxygen-poor mud. The plant tolerates regular flooding by seawater and helps bind soft marsh sediment. All parts contain cyanogenic glycosides and can poison grazing livestock, particularly when wilted. It has little ornamental use and is grown chiefly in salt-marsh and coastal restoration.

Native Range

Native across the cooler Northern Hemisphere, including the coasts of Europe, northern Asia, and North America, where it grows in tidal salt marshes, brackish shores, and inland saline wetlands.

Suggested Uses

Used in salt-marsh creation, coastal and estuarine restoration, and brackish wildlife plantings, where it binds wet sediment and adds to marsh diversity. It suits constantly wet, saline beds rather than ordinary borders. It is planted as rooted divisions or sown directly onto suitable wet ground.

How to Identify

Recognized by tufts of fleshy, half-round, channelled leaves from a stout base, resembling a grass or rush but with arrowgrass features. A leafless stalk bears a long, slender spike of many small green flowers without petals. Ripe fruits split into narrow, arrowhead-shaped segments, separating it from true grasses and rushes.

Appearance

Size & Dimensions

Height4" - 2'

Width/Spread6" - 1'

Reaches mature size in approximately 3 years

Colors

Flower Colors

green

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~14 weeks

Spring Summer

Flowering runs from May to August, with slim green spikes lengthening above the leaves. The small, petalless flowers are wind-pollinated and lack scent or nectar. Arrowhead-shaped fruits ripen from mid-summer and split to release the seeds.

Detailed Descriptions

Foliage Description

green

Growing Conditions

Sun Requirements

SunFull Sun

Requires 6-12 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 Range6.5 - 8.0(Alkaline)

357912

Soil Types

clay silt sand

Drainagewet

Water & Climate

Water Needs

High

Frost Tolerance

hardy

Time to Maturity

2-3 years

Care & Maintenance

Care Guide

Sea arrowgrass grows in full sun on permanently wet, saline, or brackish soils, and depends on the waterlogged, salty conditions of coastal marshes. It tolerates tidal flooding and low-oxygen mud that few plants endure but cannot cope with dry or freshwater garden soil for long. Propagation is by seed sown on wet saline substrate or by division of the rootstock. In cultivation it needs a constantly wet, salted bed and full sun to persist. The foliage holds cyanogenic compounds and is hazardous to grazing animals, especially when cut and wilted. It needs no feeding and little care once established in suitable wet ground.

Pruning

No pruning is needed. Old foliage can be cleared in late winter before new growth, though it usually breaks down naturally in the marsh. Removing ripe seed heads limits self-sowing where spread is not wanted.

⚠️ Toxicity Warning

Toxic to pets and humans

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Perennial

Triglochin maritima

common arrowgrass

Juncaginaceae

Northern Hemisphere coasts (Europe, Asia, North America)

Native to North America

SunFull Sun

WaterHigh

HardinessZones 3–8

Overview

Native Range

Native across the cooler Northern Hemisphere, including the coasts of Europe, northern Asia, and North America, where it grows in tidal salt marshes, brackish shores, and inland saline wetlands.