Sium spp.

water parsnip

Apiaceae

North America, Europe, and temperate Asia

Attracts Pollinators

Native to North America

SunFull Sun – Part Shade

WaterHigh

HardinessZones 3–8

Overview

Sium spp. is a genus of perennial herbs in the carrot family that grow in wet ground and shallow water across the Northern Hemisphere, with about ten species. Plants arise from a cluster of fleshy roots and produce stout, hollow, ridged stems 1.5-6 feet (0.5-1.8 m) tall. Leaves are pinnate, divided into 7 to 17 lance-shaped, sharply toothed leaflets each 1-5 inches (2.5-13 cm) long; submerged leaves on some species are more finely dissected. Tiny white flowers form compound umbels 1.2-3 inches (3-8 cm) across, framed by narrow bracts, opening in mid to late summer. The umbels give way to small ribbed, rounded fruits. Plants spread by seed and by stout roots, forming colonies in marshes, ditches, and stream margins. Sium spp. resembles the deadly water hemlock (Cicuta spp.), and the foliage of some species can sicken livestock. Top growth dies back to the roots over winter and resumes in spring.

Native Range

Sium spp. species are native to wetlands across North America, Europe, and temperate Asia, with S. suave widespread in North America and S. latifolium in Europe. They grow in marshes, fens, ditches, pond margins, and slow streams, in shallow standing water or saturated mucky soils at low to middle elevations.

Suggested Uses

Grown at pond and stream margins, in bog gardens, and in constructed wetlands for water filtering and wildlife cover, spaced 18-24 inches (45-60 cm) apart. The vigorous, colony-forming roots leave it hard to contain in small water gardens. The resemblance to water hemlock and the toxicity of some foliage limit its use near livestock and children.

How to Identify

Recognized by hollow ridged stems in wet ground and once-pinnate leaves with 7 to 17 sharply toothed, lance-shaped leaflets, topped by compound umbels of tiny white flowers 1.2-3 inches (3-8 cm) across with narrow bracts. The single row of leaflets separates it from the more divided foliage of water hemlock (Cicuta spp.); the two are easily confused where they grow together, and Cicuta spp. is highly poisonous.

Appearance

Size & Dimensions

Height1'6" - 6'

Width/Spread1'6" - 3'

Reaches mature size in approximately 2 years

Colors

Flower Colors

white

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~4 weeks

Summer

Flowering occurs in mid to late summer, mainly July through September. The compound umbels open over two to four weeks, and a colony flowers across an extended period. Ribbed fruits ripen in late summer and fall.

Detailed Descriptions

Foliage Description

green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 6-10 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 Range6.0 - 7.5(Neutral)

357912

Soil Types

loam silt clay

Drainagewet

Water & Climate

Water Needs

High

Frost Tolerance

hardy

Time to Maturity

2-3 years

Care & Maintenance

Care Guide

Sium spp. grows in full sun to part shade in shallow water or constantly wet, mucky soil and does not tolerate dry ground. It suits pond margins, bog gardens, and rain gardens, and spreads by root and seed into standing colonies. Plants are raised from seed sown in fall or by division of the roots. Aphids may gather on the flower stems. Because the genus resembles water hemlock and some foliage is toxic, plants are kept away from areas grazed by livestock.

Pruning

No routine pruning is needed. Flowering stems can be cut back after seeding to limit spread in small water features. Foliage dies down in late fall and is cleared from ponds to reduce decaying matter in the water.