The fast-growing, invasive Mimosa (Albizia julibrissin), a small, deciduous tree, is also called a silk tree. It produces beautiful white or pink flowers without petals that are attractive to hummingbirds, bees, and butterflies. Horticulturists say the name Mimosa applied to this tree is technically inaccurate. The true Mimosa--Mimosa pudica and Mimosa tenuiflora--contains more than 400 species of herbs and shrubs. The silk tree is generally not recommended as an ornamental because of several problems.
Mimosa trees spread aggressively. A Mimosa produces hundreds of seed pods. New trees pop up everywhere: by the foundation of your house, in your neighbor's yard, in cracks in sidewalks, by fences, in your flowers, you name it. It commonly grows alongside highways and country roads in the South. Some disgruntled gardeners argue Mimosas should be removed whenever possible. It has been included in a list of the 100 worst invasive plants in the world.
The Mimosa is particularly susceptible to a fungus, Fusarium oxysporum (also called fusarium wilt), which clogs the tissues that carry water and sap in the tree. Early on, the wood in the roots or under the bark turns brown. Later on, the leaves turn brown and the bark cracks, sometimes exuding a white, frothy fluid. A Mimosa can die a month after the first symptoms appear, or it may survive another winter--but death is inevitable. Although the top of a tree might be dead, sprouts can still pop out of the trunk.
No known way exists to control this fungus. The only option is to replace the tree with another species. After the tree dies, the fungus can continue to ooze from cracks in the bark and can be present in seeds. It is spread by water and can contaminate shoes and garden equipment.
Ugly, Messy Seed Pods
Mimosa grows hundreds of brown, bean-like seed pods that are about 6 inches long. Hundreds of these hang from every branch. After the leaves have dropped, in the fall, the ugly seed pods still hang from the branches. To many, a Mimosa in the wintertime with these seed pods hanging from bare branches looks extremely yucky.
Rapid Growth, Short Life
The Mimosa grows extremely fast. If you make the mistake of planting it too close to a sidewalk, you risk having roots buckle the concrete. Like many fast-growing trees, silk trees don't live very long. Five to ten years is the usual lifespan.