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Chromolaena spp.

Asteraceae Americas

Attracts Pollinators Attracts Butterflies Drought Tolerant Container Friendly

Native to North America

SunFull Sun – Part Shade

WaterLow · drought-tolerant

HardinessZones 9–11

Overview

Chromolaena spp. is a genus of about 165 species of perennial herbs and soft-wooded shrubs in the daisy family, native to the warmer parts of the Americas. Plants form upright to scrambling stems 1-3 m (3-10 ft) tall, with opposite, triangular to oval leaves that are often three-veined and aromatic when crushed. The small flower heads lack ray florets and are made up of tubular disc florets in white, pale blue, lilac, or pinkish tones, gathered in flat-topped clusters at the stem tips. Wind-borne seeds carry a tuft of bristly hairs that aids long-distance spread. Species grow in clearings, grassland, roadsides, and disturbed ground. The species C. odorata (Siam weed) has spread far beyond its native range and is a serious invasive weed across the tropics of Africa, Asia, and the Pacific, where it forms dense thickets. Rapid growth and prolific seeding keep the genus to controlled settings.

Native Range

Chromolaena spp. is native to the Americas, from the southern United States through Mexico, Central America, the Caribbean, and South America. Species grow in open woodland, savanna, grassland, and disturbed ground in warm climates.

Suggested Uses

Chromolaena spp. is grown in some warm-climate gardens for its clustered flowers and as a nectar source for butterflies and bees. Use is limited by the invasive behaviour of several species, so planting is confined to regions where the genus is not a weed. C. odorata is studied widely in weed management.

How to Identify

Identify Chromolaena spp. by its opposite, often three-veined triangular leaves, aromatic when bruised, and its flat-topped clusters of small rayless flower heads in white to lilac. Each head holds only tubular disc florets, and the seeds bear a pappus of bristly hairs. The opposite leaves separate it from many alternate-leaved daisy-family weeds.

Appearance

Size & Dimensions

Height3' - 10'

Width/Spread3' - 8'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~8 weeks

Fall Winter

Flowering occurs mainly in the dry season in the tropics, often autumn to winter, and in late summer to autumn in cooler parts of the range. The clustered heads open over several weeks and produce abundant wind-dispersed seed. In frost-free areas some species flower over a long period.

Detailed Descriptions

Flower Description

white to lilac

Foliage Description

green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

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 Range5.0 - 7.5(Neutral)

357912

Soil Types

sand loam clay

Drainagewell drained

Water & Climate

Water Needs

Low

Frost Tolerance

tender

Time to Maturity

1-2 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Chromolaena spp. grows in full sun to light shade in a wide range of soils, from sandy to clay, and tolerates poor, dry ground once established. Plants accept a soil pH of about 5.0-7.5 and need little water after establishment. Growth is fast, and stems resprout readily from the base after cutting. Frost kills top growth, and most species are tender below about 0 C (32 F). Because several species seed prolifically and spread, container culture or regular removal of seed heads keeps them in check.

Pruning

Stems are cut back after flowering to limit seeding and keep plants compact, and hard pruning in late winter renews growth. Removing seed heads before they ripen reduces unwanted spread. Plants resprout quickly from the base.