May 2009

But It’s So Beautiful!
Mimosa

Contact: Lane Heimer, MDA | 410-841-5920

Mimosa. Photo: Lane Heimer, MDA

And beautiful it is...

ANNAPOLIS, MD (April 3, 2009) - The mimosa tree (Albizia julibrissin) has always been appreciated by homeowners and gardeners for its wonderful fragrant, showy flowers, delicate leaves and draping canopy. First brought to the United States around 1745 as an ornamental tree, it has now become a troublesome invasive tree in Maryland and a competitor to native trees and bushes. Because the airy blossoms begin to appear this month, MISC has chosen mimosa as the May Invader of the Month.

A fast growing tree, mimosa has escaped from the many yards in which it was planted and is invading riparian and natural areas as well as disturbed habitats such as roadsides and old fields. As with many invasive plants, it can grow in a wide range of soil conditions, produce many seeds, and has the ability to resprout vigorously when it is cut or damaged. Dense stands of Mimosa trees can form canopies and shade out desirable native species. Mimosa prefers full sun, but can tolerate partial shade as well. Originally from Asia, mimosa, also known as the silk tree, is currently found throughout the eastern and southwestern United States.

Mimosa is a flat-topped, thornless, deciduous tree with single or multiple stems which can grow to be 20-40 feet tall. The thin bark is light in color and smooth. It is a legume with delicate, fernlike leaves that are bipinnately compound, meaning they are divided into sections and the sections are divided again into smaller sections. The leaves are asymmetric, with the midrib closer to and parallel to one of the margins (leaf edge). It may be confused with honey locust, because both are in the Pea family and have bipinnate leaves.

Mimosa has very showy, fragrant, pink flowers. An unusual characteristic of this tree is that the flowers and leaves close overnight. Changes in water pressure in specialized structures at the base of the petioles and leaflets cause the movement. The flowers give way to numerous flat, tan colored seed pods, which ripen in late summer, and look like large beige lima bean pods. Large quantities of seeds are produced. The papery pods can be easily dispersed by wind and water. Although few wildlife species feed on this plant, birds can aid in seed dispersal by activity among the branches. This allows this plant to quickly spread and invade new areas. In addition to this, mimosa seeds have impermeable seed coats that allow them to remain viable and dormant for years, making the tree difficult to eradicate. Mimosa is rarely recommended as an ornamental plant in the US, but its feathery blossoms can be very attractive. Excellent native alternatives to mimosa include flowering dogwood (Cornus florida), redbud (Cercis canadensis) and serviceberry (Amelanchier arborea). Check with the Maryland Native Plant Society (www.mdflora.org) for plant recommendations for your particular area.

Mimosa is susceptible to cold and disease, especially to mimosa wilt a fungal disease caused by a species of fusarium. This susceptibility can cause them to be short lived trees, but.the disease does not seem to have a serious impact on mimosa populations.

Mimosa can be controlled using a variety of preventative, mechanical and/or herbicide controls. Most important is preventing the spread of mimosa by removal of existing plants within the landscape and educating others of the dangers of planting this species. Mechanical controls include hand pulling of seedlings when they are large enough to grasp. For large trees, girdling or cutting at the ground level and then following up with repeated cutting or herbicide treatment can give good control. It is best to girdle/cut the trees when they at or before flowering, to prevent seed production. Herbicide treatments can be done as foliar treatments, basal bark treatments or cut stump treatments. Recommended herbicides include glyphosate, triclopyr and clopyralid. There are no known biological control agents for mimosa.

For more information about this and other Invasive Species of Concern, visit www.mdinvasives.org

Mimosa leaf and flower K. Kyde, MD DNR