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Iva spp.

Asteraceae

North America (especially coastal and alkaline regions)

Drought Tolerant

Native to North America

SunFull Sun

WaterMedium · drought-tolerant

HardinessZones 4–9

Overview

Iva spp. is a genus of annual and perennial herbs and shrubs in the daisy family, Asteraceae, native mainly to North America. The plants are wind-pollinated and inconspicuous in flower, with small greenish nodding heads of tubular florets borne in leafy spikes rather than showy daisy blooms. Across the genus, plants range from low annuals to coarse perennials and shrubs roughly 1 to 8 feet (0.3 to 2.4 m) tall, with opposite lower leaves that become alternate up the stem. The genus grows in salt marshes, coastal flats, alkaline ground, and disturbed sites, with species such as I. frutescens (marsh elder) forming shrubby stands along tidal shores. I. annua (sumpweed) was once cultivated by Indigenous peoples of eastern North America for its oily seeds before maize agriculture displaced it. The wind-borne pollen is a recognised cause of hay fever, much like that of the related ragweeds (Ambrosia spp.). The plants carry little ornamental flower display and are grown mainly for habitat, coastal planting, and ecological interest.

Native Range

Iva spp. is native mainly to North America, from coastal salt marshes and alkaline plains to disturbed inland ground, with a few species reaching Central America and the Caribbean. Several species are characteristic of tidal shorelines and saline flats.

Suggested Uses

Iva spp. is used in coastal and salt-marsh restoration, shoreline stabilisation, and wildlife and habitat plantings on saline or alkaline ground. The salt tolerance of species such as I. frutescens suits difficult tidal and brackish sites. The plants are grown for ecological value rather than for flower display.

How to Identify

Plants have square to ridged stems with opposite lower leaves that become alternate higher up, and small greenish, nodding flower heads set in the axils of leafy bracts. The heads hold only tubular florets, lack showy ray petals, and shed wind-borne pollen. The greenish rayless nodding heads in leafy spikes, on plants of marsh and alkaline ground, separate Iva spp. from true ragweeds and from marsh asters.

Appearance

Size & Dimensions

Height1' - 8'

Width/Spread1' - 5'

Colors

Flower Colors

green

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~8 weeks

Summer Fall

Flowering occurs in late summer and autumn, roughly August to October, when the greenish wind-pollinated heads release pollen. The flowers have no showy petals and little visual colour. The pollen is a common late-season hay-fever trigger in areas where the plants are abundant.

Detailed Descriptions

Foliage Description

green

Growing Conditions

Sun Requirements

SunFull Sun

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 - 8.5(Alkaline)

357912

Soil Types

sand clay loam

Drainageaverage

Water & Climate

Water Needs

Medium

Frost Tolerance

hardy

Time to Maturity

2-3 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Iva spp. grows in full sun in a wide range of soils, including saline, alkaline, wet, and poor ground that many plants will not tolerate. Coastal and marsh species withstand salt spray, tidal flooding, and brackish water, while inland species grow on dry alkaline flats. Perennial and shrubby species are hardy in roughly USDA zones 4 to 9, dying back in winter where cold. Plants need little care and can self-seed and spread on open ground. Propagation is by seed, and shrubby species can also be grown from cuttings or by division.

Pruning

Shrubby species can be cut back in late winter to remove old stems and keep a compact shape. Annual and herbaceous species die back and are cleared at the end of the season. Cutting flowering stems before pollen is shed can reduce hay-fever exposure near the plants.