A low, spreading crown of fern-like foliage. A flamboyant display of unique, powder-puff flowers in vibrant pink. Fast-growing, but never outgrowing limited spaces. What’s not to like about the Mimosa Silk Tree? This striking tree always turns heads, especially when in bloom, and it is easy to care for, and undemanding. It also has the appealing ability to ‘go to sleep’ at night, or during rain, with the leaves folding up tightly even if the tree is shaken hard. No wonder the Japanese call it nemunoki, the ‘sleeping tree’. In its homeland Persians call it shabkhosb, or ‘night sleeper’, and it is also known as the Persian Silk Tree. It is a relative of the true yellow mimosa tree, not part of that large group, but whatever we call it, this small tree makes a great addition to any garden, and it’s a particularly good choice for smaller ones, or for courtyards and enclosed areas. With a stunning form available with rich red to chocolate-colored leaves, it can also be a valuable foliage plant, even when not in flower.
Sometimes it’s a shame that trees usually grow upright, taller than they are wide, because we often need width for shade, without a lot of height. This is where the Mimosa Silk Tree really belongs, in places where we want some shade, but not much height. Easily trained into a single trunk with a broad umbrella-like flattened crown, this unusual form has lots of uses.
Do you have a smaller, courtyard garden? Then you probably dream of sitting out there, enjoying the summer, except that it gets too hot. You don’t want to fill the space with some huge tree, blocking windows. Then plant a Mimosa Silk Tree. With a 6 to 10-foot slender trunk, the crown will be 8 to 12 feet across within a few years, and that crown only adds a few feet to the overall height. It’s like a living shade umbrella.
In a larger space, several Mimosa Silk Trees scattered over an area of lawn, or grown in open spaces among paving, make a lovely sight, creating an attractive grove of shade and color, with the ferny foliage never dominating or looking crowded. You can also grow these trees as an avenue along a driveway or broad path, spacing them well apart as punctuation points, not a continuous cover. In hot, dry areas this is a great way to cool down a space without making it look full and overpowered by trees.
The Mimosa Silk Tree will also grow well in a large planter box or tub, for many years, and being drought-resistant, if you miss watering it from time to time it will be just fine. It gives clear passage underneath, often necessary in smaller spaces, yet throws shade and looks fabulous when it is in bloom.
An interesting way to grow the Mimosa Silk Tree is on a wall. This is especially useful in zone 6, which is the lower limit for winter hardiness. On a sunny, south-facing wall, planted in the drier soil right at the base of the wall, this tree will be right at home. Tie back the branches on nails, or along wires stretched across the wall, and trim back hard to the main branches just before the buds open in spring. This is a spectacular way to cover a wall, and a way of growing this tree in colder areas, without taking up garden space at all.
There is a form of this tree called the Summer Chocolate Silk Tree, with rich burgundy-red leaves that turn chocolate brown in summer. After a couple of years to become established and build up strength, you can grow this tree as a shrub. Cut it back hard in spring and it will push up branches 3 to 4 feet long, covered in lush, richly-colored foliage. What a great backdrop to green shrubs and flowers that would make.
The Mimosa Silk Tree is a small tree growing typically between 15 and 25 feet tall in gardens, but capable of growing to as much as 40 feet tall in the wild. When young it has a broad, umbrella-like form becoming in time, if untrimmed, a rounder shape, with its spread roughly equaling or exceeding its height. It can be grown with a single trunk, or as a multi-stem tree, whichever is more appropriate for your needs. The bark is smooth to slightly rough, of a dark gray-brown color. Older stems develop vertical stripes of lighter brown, in narrow striations.
The foliage of the Mimosa Silk Tree is remarkable, and very appealing. The leaves are between 10 to 20 inches long, and 5 to 10 inches wide. The long central stem has between 4 and 6 shorter stems along each side, arranged in pairs. Then, those stems have 20 to 30 pairs of tiny leaflets along them, each one just ¼ inch long. This abundance of small leaves on long stems gives the tree a ferny, soft look, and the leaves have a silky touch too. This tree has a unique open, light and airy look, so even in smaller spaces it looks graceful, and never overpowering.
The flowers are remarkable, and a highlight of the season. They are carried in clusters at the end of each growing tip. The base of each flower is a slender green tube of reduced petals, and from it grows many, many stamens, each one thread like, white at the base turning brilliant pink for most of their length. Each one is tipped with a tiny dot of yellow pollen, and they fan out like a pom-pom, or perhaps a crest found adorning the head of some tropical bird. With these exotic blooms growing all along the branches, a tree is bloom is gorgeous, and does seem to have been decorated in fine silk by a skilled craftsman. A sweet fragrance flows from the blooms, and bees, butterflies and other insects, as well as hummingbirds, love to visit the flowers for nectar.
Blooming continues for weeks throughout the summer, eventually ending as the blooms turn into seed pods that change from green to mid-brown as they ripen. These pods are 6 to 7 inches long, broad and flat, and they decorate the tree through much of the winter, after the leaves have fallen.
The Mimosa Silk Tree is hardy from zone 6 to zones 9 and 10, thriving in all warm climates, both humid and dry ones. In zone 6 there may be some winter-kill of the ends of the branches, especially when young trees are growing vigorously. This doesn’t affect the new growth, but you could remove those dead tips once the tree re-sprouts, although they will soon be hidden by the new leaves.
Ordinary to dry soil suits this tree perfectly, and we recommend it for all types of soil, from sand to clay and acid to alkaline. It just needs good drainage, and a dry location is much better than a wet one. Once established this tree is very drought resistant, and it is a great choice for dry climate regions such as the south-west.
Planting procedures for this tree are normal, with no special requirements. Some basic soil preparation is helpful, and weekly watering during the first season, while the roots grow out, but otherwise this tree is very easy to plant and establish.
Tough and reliable, the Mimosa Silk Tree needs no special care at all. If you are growing a single trunk, remove any shoots that might grow from the main stem. Trimming the upper parts of the crown every year or two will retain and accentuate the umbrella form of this tree.
This very drought resistant tree needs little watering. Remember though, that while its drought resistance is good, growth will not be rapid in very dry soil, so for young trees we recommend periodic deep soaking during very dry conditions, to keep your tree growing strongly.
Pests are normally not a problem, and deer leave this tree alone too. Although diseases can attack this tree, this normally happens only in wetter, poorly-drained soils. So if the drainage is excellent, and the soil not regularly wet, there should be no problems.
The plant world is vast, and only a few trees make it into our gardens, for either practical or historical reasons. This is certainly true of the Mimosa Silk Tree, because we normally see just one species – Albizia julibrissin – while the genus Albizia has over 160 members. Much of the reason for this is the distribution of these plants. They grow almost exclusively in subtropical and tropical areas, around most of the world, from the Americas through Asia and even into Australia. Only the Mimosa Silk Tree will grow in cooler areas, so it’s the only one seen, although a few others might be found growing in zone 10. As well, this tree is undoubtedly the most colorful, so its easy to see why it was brought to southern Europe long ago by an adventurous Italian naturalist, Filippo degli Albizzia, in 1749. He was undoubtedly exploring in the Middle East, and found this tree in Persia, today’s Iran. It must have caused a sensation back in Italy. Obviously named after him, the second name seems less strange when we know it was created from the Persian name gul-i abrisham, which literally means ‘flower of silk’.
It is likely that the plant we grow today as simply Albizia julibrissin is in reality a form not at all from Persia, but from much further east, in Korea and northern China. This plant, called ‘forma rosea’, or simply ‘Rosea’, was found in Korea in 1918, by Ernest H. Wilson, the famous plant explorer. He made numerous expeditions to China and the East, and he contributed many plants to our gardens. He found this tree growing in the courtyard of his hotel in Seoul and collected some seeds. Just one seedling survived when they were grown back at Harvard’s Arnold Arboretum, but this tree was remarkable for tolerating much colder conditions than others. Since today we routinely assume that the Mimosa Silk Tree survives in zone 6 – which it does – and the flowers have the upper part pink and the lower part white, as originally described for Wilson’s plant, then we are almost certainly growing today descendants of that original, and not the earlier ones from Italy. Our trees also stay smaller, with the characteristic umbrella form, so this tree is very superior to the original wild plant, for size, form and the intensity of the flower color.
We are not confined to plain green foliage with the Mimosa Silk Tree, because we have the beautiful form called ‘Summer Chocolate’. This tree is also called the Purple-leaf Mimosa, and the foliage begins the season a deep, rich burgundy red, darkening through summer into an intense reddish chocolate-brown. This makes an outstanding display right from the get-go, without even waiting for blooms. ‘Summer Chocolate’ was found as a single seedling among thousands, grown in Japan by Dr. Masato Yokoi in a breeding program he created. In 2003 it was patented in the U.S. by Hines Nursery, from Irvine, California. All plants with that name are grown from grafted stem pieces, not seed, of that original amazing plant.
Although we don’t have a profusion of different Mimosa Silk Trees, we hardly need them, so great is the original. With the Summer Chocolate Silk Tree as well, and its amazing foliage, we have plenty to enjoy. Whether its foliage, flowers, or both, this tough, drought-resistant tree is a stand-out choice for every warmer garden.