Persian silk trees: flowers, care overwintering of Albizia julibrissin
The filigree leaves and showy flowers of the Persian silk tree, also called the mimosa tree, make it hard to deny its direct relationship to the mimosa.
Persian silk trees are generally not very hardy, hence their limited distribution in Central European landscape gardening. Keep reading to learn how to grow Persian silk trees in your garden and which varieties of Albizia julibrissin are most suitable.
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Persian silk tree: flowers, origin and properties
Persian silk trees (Albizia julibrissin) are called as such because of their close relationship and strong resemblance to acacias (Acacia). Along with mimosas (Mimosa), both trees are members of the same subfamily, namely the mimosa family known as Mimosoideae, which belongs to the legume family, Fabaceae. Due to the fact that they fold up their leaves overnight or during dry or rainy periods, they are known as shabkhosb in Persian, meaning ‘night sleeper’. They are also known as Lankaran acacias, mimosa trees, Japanese silk trees, Chinese silk trees or sleeping trees, the latter of which is fitting as, in Chinese medicine, the bark of silk trees is used in sedatives.
Originating from southern Asia, Persian silk trees are now widespread in Asian countries, but also in South Africa and parts of South America. Whilst these trees have the potential to be invasive, this does not apply to our part of the world due to the cold temperatures.
Persian silk trees are deciduous shrubs or trees, depending on the region and climatic conditions, but can reach a height of 6 to 8m under optimal conditions. This tree forms an umbrella-shaped crown and usually grows multi-stemmed and shrubby in Central Europe due to frequent frost damage.
The alternate leaf fronds are bipinnate and grow to about 20 to 30cm long. A distinctive feature of this perennial is that the leaflets fold up at night and during drought. After a certain age and in warmer regions, Persian silk trees flower from July to August and later develop thin legumes with 8 to 12 seeds. The fragrant, hermaphrodite flowers grow in clusters and look like pink and white silky pom-poms.
Depending on the variety, Persian silk trees are only conditionally hardy in the UK. They often require winter protection at the beginning, but you can also plant them in a container and move them indoors when it gets too cold. Due to its brittle wood and thin, delicate bark, these trees are easily damaged during storms. They usually reach an age of only 10 to 20 years.
Is the Persian silk tree bee-friendly? Whilst the delicate fragrance of the exotic flowers also attracts insects, the Persian silk tree is not a great enrichment for native bees.
Persian silk tree varieties
One thing in which the many varieties of Albizia julibrissin differ is their degree of frost hardiness. Take this into consideration if you plan on keeping this tree somewhere where it is not warm.
- Albizia julibrissin ˈOmbrellaˈ: this commercial variety is quite similar to regular silk trees, but it is very vigorous and tolerates temperatures of -15 °C for a short time. Albizia julibrissin ˈOmbrellaˈ grows umbrella-shaped and reaches a height of about 8 – 10m.
- Albizia julibrissin ˈErnest Wilsonˈ: this variety is much more frost-hardy than the regular species. It can withstand temperatures down to about -23 °C. Due to the somewhat stocky growth with a height of 4 – 5m, it is more round in shape.
- Albizia julibrissin ˈSummer Chocolateˈ: with its unusual foliage, this commercial variety makes quite an impact. The leaves, which are fresh green when they first appear, later turn a chocolate brown and finally turn golden-yellow in the autumn. The ˈSummer Chocolateˈ variety of silk tree reaches a height of about 2 – 4m and is hardy to about -17 °C.
- Albizia julibrissin ˈPendulaˈ: the peculiarity of this variety lies in the arching, overhanging shoots with pink flowers. It can reach a height of up to 7m and can withstand temperatures down to about -17 °C.
- Albizia julibrissin ˈEvey’s Prideˈ: the deep brown-red foliage of this variety adds exciting pops of colour to any garden. It grows up to 7m high and bears bright pink flowers. This variety is winter hardy down to about -17 °C.
Did you know? There are two varieties of silk tree, namely Albizia julibrissin var. rosea, whichis somewhat more frost hardy, and Albizia julibrissin var. mollis, whichis distinguished mainly by its densely hairy shoots. However, these varieties are hard to get hold of in the UK.
Planting Persian silk trees
Persian silk trees like a sunny, warm location that is protected from the wind. A south-facing wall, for instance, is ideal. These trees are not fussy when it comes to soil. That said, they do need something well-draining, so light, sandy soils are preferable to heavy clay soil.
Aesthetically speaking, it is best to plant just one solitary Persian silk tree. The best time to plant it is after the last frosts around mid-May. To do this, first dig a generous planting hole. Mix the excavated soil with sand or gravel to optimise permeability in clay-rich, heavy soils. Then simply place the plant in the hole, press down and water everything in.
Planting a Persian silk tree in a container: Albizia julibrissin varieties with a slightly lower growth height are particularly suitable as container plants. Especially in regions with harsher climates, this option is ideal for safe overwintering. Start by creating a drainage layer of expanded clay at the bottom of the container, and then follow this with a well-drained, humus-rich soil. Our Plantura Organic All Purpose Compost is well-suited for this purpose, as it contains added lime and magnesium as well as organic fertiliser to optimally support your Persian silk tree throughout the growing period. Due to its high humus content, it is rich in nutrients and also retains water well, making it ideal for container and bed plants.
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Plant care: pruning, fertilising and more
Persian silk trees cope well with dry soil from time to time. You only need to provide additional water during dry periods to newly planted trees. Water Persian silk trees in containers as soon as the top layer of soil is completely dry, or if you notice the leaves start to fold or curl.
Fertilise your silk tree in the spring with a high-quality slow-release fertiliser. Since these trees are not very salt-tolerant, opt for a primarily organic fertiliser rather than a mineral one. Our Plantura Flower Food, for instance, is ideal, as it releases its nutrients gradually, thereby accommodating the sensitivities of the silk tree.
Annual pruning in the spring can be useful, especially when growing a Persian silk tree in a pot. It allows you to adjust the shape as desired and somewhat limit the size. Persian silk trees planted in the ground can be trained to grow more shrub-like by pruning. This mainly involves the removal of long, troublesome shoots.
Tip: Persian silk trees tolerate pruning well, so can also be grown well as bonsais.
Why is my Persian silk tree losing leaves? There are several reasons as to why your Persian silk tree is losing leaves. It could be down to frost damage, a lack of light or improper care, such as too much or too little watering or fertilising. Fungal wilt disease Fusarium oxysporum, is another cause of leaf drop, and is a common and fatal disease for Persian silk trees. The first visible symptoms are yellow, stunted, wilted leaves. The best way to prevent this fungal infection is to ensure you provide your silk tree with optimal growing conditions and proper care. Remember to always check for any signs of infection when purchasing Persian silk tree plants or seeds.
Are Persian silk trees hardy?
Persian silk trees are winter hardy down to about -15 °C. As already mentioned, the degree of frost hardiness varies somewhat from variety to variety. In warmer regions, you can plant these trees outdoors provided you take appropriate protective measures. It is essential to provide Persian silk trees with winter protection, especially when they are still young. Frost-hardiness increases somewhat as they mature. In colder regions with harsher winters, opt for varieties with a higher frost-tolerance. If you live in such climates, you will be better off planting your silk tree in a container and moving it somewhere relatively dry and frost-free over the winter months. To protect outdoor silk trees from the cold, make sure you keep them somewhere sheltered and sunny. For extra protection outdoors, wrap the trunk with an insulating material such as raffia and cover the root plate with a thick layer of mulch.
Propagating Persian silk trees
One very reliable method of propagating mimosa trees is by cuttings in early summer. To do this, cut a new shoot as close as possible to the base of the plant and remove the leaves at the bottom of the cutting. Then, put the cutting in a pot filled with soil. Place somewhere bright where temperatures stay around 25 °C, and keep the soil moist. Propagation by root cuttings also works well.
Propagating Persian silk trees by seed is also a quick and reliable method. Before you can do this, you will need to treat them with hot water first. This process is known as hot water scarification. To do this, pour the seeds into a small container with around 90 °C water and leave overnight. Next, place the seeds in planting trays with potting soil and lightly cover with soil. Place everything somewhere bright and keep the soil moist. The optimum germination temperature is between 20 and 25 °C. As long as the seeds have been treated with hot water, the first seedlings will start to emerge after about 10 to 14 days.
Are Persian silk trees poisonous?
The poisonous parts of Persian silk trees are the fruits and seeds. Be sure to keep them away from small children and animals to prevent them from eating them. The sap and leaves of the silk tree do not contain toxins, so are harmless. No irritation or other reactions are expected from skin contact with Albizia julibrissin.
