Albizia julibrissin aka Mimosa

Albizia julibrissin is a deciduous tree in the pea family, Fabaceae. Gardeners know it as mimosa, silk tree or Persian silk tree. It comes from Asia, with a wild range running from Iran and the Transcaucasus east to China and Japan. In the Himalayas it grows in sunny ravines, forests and riversides up to about 6,900 feet (2,100 m). It reached the United States in the 1700s and has since escaped into the wild there.

In gardens it usually reaches 15 to 30 feet (4.5 to 9 m) tall. Its crown often spreads wider than it is tall, at 20 to 35 feet (6 to 11 m). Some sources give up to 40 feet (12 m) in height and 50 feet (15 m) in width. The tree branches low and often has several trunks. With age it forms a flat-topped, vase-shaped or umbrella-like crown. The bark is smooth and gray-brown. Young stems start lime green, turn light brown, and carry many lenticels. The leaves are bipinnate and feathery, reaching 10 to 20 inches (25 to 50 cm) long. Each tiny leaflet folds up at night or when touched. The tree leafs out very late in spring and shows no autumn colour.

From early to late summer, fluffy pink flower heads cover the top of the crown. Their long silky stamens give them a powder-puff look, and many are fragrant. Bees, butterflies and hummingbirds visit the blooms. Flat brown pods, 3 to 7 inches (8 to 18 cm) long, follow the flowers and often hang on into winter.

The tree grows fast and likes full sun and well-drained soil. It accepts clay, loam, sand, chalk, and acid or alkaline conditions. It handles drought, heat and wind, but looks lusher with steady moisture. It suits USDA zones 6 to 9 and rates H4 in the UK. Mild spells followed by cold snaps can damage new growth. A tree cut back by frost can often resprout from the base. Seedlings usually flower within three years.

Many people plant it as a patio or lawn tree for its light shade and tropical feel. Chinese medicine has long used the bark and flowers to calm anxiety and aid sleep. The dense, hard wood suits furniture and firewood. As a legume, the tree also fixes nitrogen.

The tree has serious drawbacks. Its wood is brittle, and wind, ice and snow break the limbs. Fallen leaves, flowers and pods create a lot of mess. A few thick surface roots can lift paths and patios. Fusarium wilt is common and kills the tree. Mimosa webworm, mites, cottony cushion scale and honey fungus also cause trouble. It self-seeds freely and is invasive in Florida, North Carolina and other southeastern states. Sterile cultivars such as 'Merlot Majik' and 'Summer Chocolate' reseed far less.

The young leaves and flowers are edible when cooked, and dried leaves make a tea. The seeds, however, contain toxic compounds. They can poison dogs and livestock that eat them.