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Ageratum spp.

ageratums

Asteraceae

Mexico, Central America, the Caribbean, and tropical South America

Attracts Pollinators Attracts Butterflies Deer Resistant Container Friendly

Native to North America

SunFull Sun – Part Shade

WaterMedium

Overview

Ageratum spp. is a genus of about 40 to 60 species of annual and short-lived perennial herbs in the family Asteraceae, native to Mexico, Central America, the Caribbean, and tropical South America. Plants grow 15-90 cm (6-36 in) tall on branching stems clothed in soft hairs, forming low mounds or taller open clumps. The opposite leaves are ovate to triangular, 2-8 cm (0.8-3.1 in) long, with toothed margins and a faint scent when crushed. The flower heads lack ray florets and instead form rounded, fluffy clusters of thread-like disc florets in lavender-blue, violet, pink, or white, carried in dense flat-topped groups at the stem tips. Ageratum houstonianum is the bedding plant grown for its long summer display, while A. conyzoides is a pantropical weed of fields and roadsides. The dry seeds are small and tufted, spreading on wind. All parts contain pyrrolizidine alkaloids that damage the liver if eaten, and the foliage can irritate skin. Plants are frost-sensitive and killed by the first hard freeze.

Native Range

Ageratum spp. is native to the warm regions of the Americas, from Mexico and the Caribbean through Central America to tropical South America. A. conyzoides has spread as a weed across the tropics worldwide, while A. houstonianum is grown as a garden annual far beyond its native range.

Suggested Uses

Ageratum spp. is grown as a summer bedding and edging plant, in containers, and as a cut flower for its lasting blue clusters. Compact forms are used for mass color in borders, while taller forms suit cutting beds. The pantropical weedy species have no garden use.

How to Identify

Identify Ageratum spp. by its rounded, fluffy flower heads made entirely of thread-like disc florets, with no petal-like rays, in shades of lavender-blue to white. The opposite, toothed, ovate leaves and softly hairy stems give off a faint odor when bruised. Garden forms make low, dense mounds, while weedy species are taller and more open.

Appearance

Size & Dimensions

Height6" - 3'

Width/Spread6" - 1'6"

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~20 weeks

Summer Fall

Bloom runs from late spring until frost, June to October in temperate gardens, and nearly year-round in frost-free climates. The clustered heads open over a long season and draw butterflies and small bees. Removing spent heads keeps new flowers forming.

Detailed Descriptions

Flower Description

Lavender-blue, violet, pink, white

Foliage Description

Green

Growing Conditions

Sun Requirements

SunFull Sun SunPartial Shade

Requires 4-8 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 sand

Drainagewell drained

Water & Climate

Water Needs

Medium

Care & Maintenance

Care Guide

Ageratum spp. grows in full sun to part shade on moist, fertile, well-drained soil and flowers most freely with steady moisture and warmth. It is frost-sensitive and is grown as a summer annual in cold regions, set out only after the last frost. Plants tolerate heat but wilt in prolonged drought and may stop flowering in dry soil. Tall garden forms can flop and benefit from shelter or support, while compact forms hold their shape. The pyrrolizidine alkaloids in the foliage make the plants toxic to grazing animals. Weedy species self-seed heavily and can spread into open ground.

Pruning

Spent flower clusters are sheared off through the season to prolong bloom and to limit self-seeding. Cutting tall, leggy plants back by a third encourages branching and fresh flowers. The whole plant is removed after the first frost in cold climates.