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Ageratina, Genus, adenophora, Species,

Genus & species

Crofton weed

Asteraceae Mexico and Central America

Attracts Pollinators Deer Resistant Drought Tolerant

SunFull Sun – Part Shade

WaterMedium · drought-tolerant

HardinessZones 9–11

Overview

Ageratina adenophora is a perennial, semi-woody plant growing 3-6 feet (0.9-1.8 m) tall, with purplish, glandular-hairy stems that branch in the upper half. The opposite leaves are triangular to diamond-shaped, 2-4 inches (5-10 cm) long, with toothed margins and a sticky surface. Flat-topped clusters of small white flower heads, each about 0.2 inch (5 mm) across and lacking ray florets, open from winter into spring. A single plant can produce tens of thousands of tiny, bristle-tufted seeds that spread on wind, water, and machinery, and the stems also root where they touch moist ground. The foliage contains toxins that cause fatal lung disease in horses and can sicken other livestock. It grows in disturbed ground, gullies, forest margins, and pasture in mild, moist climates. Native to Mexico, the species has become a serious weed in Australia, New Zealand, southern Africa, southern Asia, and parts of California and Hawaii. A limitation for any cultivation is its rapid spread and toxicity, which have led to legal restrictions on the plant in several countries.

Native Range

Ageratina adenophora, known as Crofton weed or sticky snakeroot, is native to Mexico and parts of Central America. It has spread through warm, moist regions worldwide, including Australia, New Zealand, India, China, southern Africa, Hawaii, and coastal California.

Suggested Uses

Ageratina adenophora is classed as a noxious or invasive weed across its introduced range and is not planted in gardens. In affected regions it is targeted for removal from pasture, gullies, and bushland. Historic ornamental use has been replaced by control programmes using cutting, herbicide, and biological agents.

How to Identify

Recognised by its purplish, sticky, glandular stems and triangular, toothed leaves arranged in opposite pairs, topped by flat clusters of small white flower heads without ray petals. The whole plant feels tacky to the touch. Its height, sticky foliage, and winter-to-spring white flowers separate it from related snakeroots.

Appearance

Size & Dimensions

Height3' - 6'

Width/Spread2' - 4'

Colors

Flower Colors

white

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~10 weeks

Flowers: February–April

Winter Spring

Clusters of small white flower heads open from late winter into spring, roughly July to October in the southern hemisphere and winter to spring elsewhere. Each plant carries many heads over several weeks. Large numbers of wind-borne seeds follow and disperse widely.

Detailed Descriptions

Foliage Description

green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 4-10 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 Range5.5 - 7.5 (Acidic to alkaline)

3579

Soil Types

loam clay sand

Drainageaverage

Water & Climate

Water Needs

Medium

Frost Tolerance

tender

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Ageratina adenophora grows in full sun to part shade and a wide range of moist soils in frost-free or mild climates. It establishes quickly from seed and from stems that root at the nodes, colonising disturbed and shaded ground alike. The plant tolerates poor soil, drought once established, and partial shade, which aids its spread. Frost checks topgrowth but established crowns resprout in mild areas. Because each plant sheds enormous numbers of seeds, removal before flowering is the main way to limit further spread.

Pruning

Plants are cut or pulled before the flower heads set seed to limit spread, and the crowns are dug out because cut stems resprout. Stem pieces are removed from the soil since they root where they lie. Repeated cutting over several seasons weakens established crowns.