Mimosa: Beauty but a Beast

The scientific name for the mimosa is Albizia julibrissin, sometimes called Persian silktree and a member of the family Leguminosae. The tree is not native to North America or Europe but was brought into western countries from Asia. Its genus is named for the Italian nobleman Filippo Albizzi who introduced it to Europe around the middle of the 18th century as an ornamental.

This fast-growing, deciduous tree has a low branching, open, spreading habit and delicate, lacy, almost fern-like foliage. These leaves have a beautiful wispy green look during a normally moist summer but start to dry up and drop in early fall. The leaves express no fall color but the tree does display a showy pink flower with a pleasant fragrance. The flowering process starts in the spring and continues throughout the summer. The fragrant, silky, pink puffy pompom blooms, two inches in diameter, appear from late April to early July creating a spectacular sight.

Mimosa's leaf arrangement is alternate and the leaf type is both bipinnately compound and odd-pinnately compound. The leaflets are small, are less than 2 inches in length, have a lanceolate to oblong shape and their leaf margins are ciliate to entire. The leaflet venation is pinnate.

This silktree grows to a height of 15 to 25 feet and has a spread that reaches 25 to 35 feet. The crown has an irregular outline or silhouette, has a spreading, umbrella-like shape and is open and yields a filtered but not full shade.

Growing best in full sun locations, Mimosa is not particular as to soil type but has low salt-tolerance. It grows well in both acid and alkaline soils. Mimosa tolerates drought conditions well but has a deeper green color and more lush appearance when given adequate moisture.

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So What's Not to Like About Mimosa

Unfortunately, the tree produces numerous seed pods that are trashy in the landscape when they fall. The tree harbors insect including webworm and a vascular wilt disease that eventually causes the trees death. Although short-lived (10 to 20 years), Mimosa is popular for use as a terrace or patio tree for its light shade and tropical look but also produces a honey-dew drip on property underneath.

The trunk, bark, and branches can be a major problem in the landscape. Its trunk bark is thin and easily damaged from mechanical impact. Branches on mimosa droop as the tree grows and will require pruning for vehicular or pedestrian clearance beneath the canopy multiple trunks. Breakage is always a problem with this multi-trunked tree either at each crotch due to poor collar formation, or the wood itself is weak and tends to break.

The litter problem of the blooms, leaves, and especially the long seed pods requires consideration when planting this tree. Again, the wood is brittle and has a tendency to break during storms though usually, the wood is not heavy enough to cause damage. Typically, most of the root system grows from only two or three large-diameter roots originating at the base of the trunk. These can raise walks and patios as they grow in diameter and makes for poor transplanting success as the tree grows larger.

Unfortunately, Mimosa vascular wilt is becoming a very widespread problem in many areas of the country and has killed many roadside trees. Despite its picturesque growth habit and its beauty when in bloom, some cities have passed ordinances outlawing further planting of this species due to its weed potential and wilt disease problem.

Mimosa Is a Major Invasive

The tree is an opportunist and a strong competitor to native trees and shrubs in open areas or forest edges. The silktree has the ability to grow in various soil types, the ability to produce large amounts of seed, and an ability to resprout when cut back or damaged.

It forms colonies from root sprouts and dense stands that severely reduce the sunlight and nutrients available for other plants. Mimosa is often seen along roadsides and open vacant lots in urban/suburban areas and can become a problem along banks of waterways, where its seeds are easily transported in water. 

Here are the methods of control:

• Mechanical Control - Trees can be cut at ground level with a power or manual saw and is most effective when trees have begun to flower.  Because mimosa will sucker and resprout you will have to do a follow-up chemical treatment but on a much smaller scale.
• Chemical Control - Trees can be controlled by applying a 2% solution of glyphosate (Roundup®). A thorough foliar application of this herbicide will kill entire plants through leaf and stem uptake to actively growing roots that prevent further cell growth.