Ageratina riparia
mist flower
Overview
Ageratina riparia is a sprawling perennial herb that grows 12-40 inches (30-100 cm) tall, with slender reddish stems that root where they touch moist ground. The opposite leaves are lance-shaped, 1-3 inches (2.5-8 cm) long, with toothed margins and a pointed tip. Flat-topped clusters of small white flowerheads, each about 0.2 inch (5 mm) across, open at the stem tips, each head holding 10 to 30 tiny tubular florets. Flowering occurs mainly in late winter and spring, after which the heads release large numbers of light, wind-borne seeds tipped with white bristles. Native to Mexico and the Caribbean, it has naturalised widely in warm, moist regions including eastern Australia and New Zealand, where it spreads along creek banks, gullies, and damp forest margins. It forms dense mats that smother low-growing native plants and is listed as an environmental weed in several Australian states. Plants regrow readily from rooting stem fragments as well as seed, so disturbed stands recover quickly. It grows fastest in shaded, moist sites and slows in full sun and dry soils, which limits its spread into open, drier country.
Native Range
Ageratina riparia is native to Mexico and the Caribbean. It has naturalised in warm, moist parts of eastern Australia, New Zealand, Hawaii, and southern Africa, where it grows along streams and in damp forest.Suggested Uses
Ageratina riparia is not planted in gardens within its naturalised range, where it is managed as an environmental weed of creeks and moist forest. In its native Central American range it occurs as a wayside and streamside plant rather than a cultivated ornamental.How to Identify
Appearance
Size & Dimensions
Height1' - 3'4"
Width/Spread2' - 4'
Reaches mature size in approximately 1 years
Bloom Information
Detailed Descriptions
Foliage Description
greenGrowing Conditions
Sun Requirements
Requires 2-6 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
Care & Maintenance
Care Guide
Ageratina riparia grows in moist, partly shaded sites on a range of soils and spreads fastest along creek banks and in damp gullies. It tolerates light frost in USDA zones 9-11, with top growth cut back by harder frost before reshooting from the base. It establishes from seed and from stem fragments that root at the nodes. Growth slows in full sun and dry ground. In regions where it has naturalised it is treated as an environmental weed and managed by removal rather than cultivation. Cut or pulled plants reshoot unless the rooting stems are fully removed.Pruning
Cutting back spreads the plant unless rooting stems are lifted at the same time, since cut nodes resprout. Removing flower heads before seed set reduces spread by wind-blown seed. Slashing alone tends to thicken low growth.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
winter