Persian silk tree: care, flowering & 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.
The plant’s limited distribution in Central European landscape gardening is mainly due to the fact that the Persian silk tree (Albizia julibrissin) is not sufficiently hardy in most cases. In this article, you will learn how you can grow the decorative Lankaran acacia in your garden and which varieties of Albizia julibrissin are best suited for this purpose.
Persian silk tree: flower, origin and properties
The Persian silk tree is sometimes referred to as a night sleeper because its leaves fold up overnight or during dry periods. In Chinese medicine, the bark of the tree is used in sedatives, which gives additional meaning to the synonym. The silk the name refers to is silk acacia, because of its close relationship and strong resemblance to the acacias (Acacia). Like the mimosa (Mimosa), these belong to the same subfamily as the Persian silk tree – the mimosa family (Mimosoideae). They are all classified in the legume family (Fabaceae). Persian sleeping tree, mimosa tree, Japanese silk tree, and Chinese silk tree are other synonyms describing the same plant based on their respective ranges. The original home of the Persian silk tree is southern Asia. Nowadays, the mimosa tree is widespread in Asian countries, but also in South Africa and parts of South America. The plant shows invasive spread potential; however, this does not apply to our region due to the cold.
The deciduous plant grows as a shrub or tree, depending on the region and climatic conditions, reaching a height of 6 to 8 m under optimal conditions. The Persian silk 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 30 cm long. A distinctive feature of the perennial plant is that the leaflets fold up at night and during drought. After a certain age and in warmth-favourable locations, the Persian silk tree develops flowers in midsummer and later thin legumes with 8 to 12 seeds. The fragrant, hermaphrodite flowers of the mimosa tree are clustered together in head-shaped flower heads and give the plant its characteristic appearance with its pink or white, long stamens from July to August.
Since the Persian silk tree, depending on the variety, is only conditionally hardy in our country and often requires protection at the beginning, planting it in a container is also suitable. Due to its brittle wood and thin, delicate bark, the plant is often damaged during storms. It usually reaches an age of only between 10 and 20 years and is therefore not very long-lived.
Is the Persian silk tree bee-friendly? Although the exotic flowers with their delicate fragrance also attract insects, the Persian silk tree is not a great enrichment for native bees.
The most beautiful Persian silk tree varieties
The different varieties of the Albizia julibrissin differ, among other things, in the degree of frost hardiness. Be sure to pay attention to this if the future location of the plant is not in a warm region. We have described this and other characteristics of the varieties below.
- Albizia julibrissin ˈOmbrellaˈ: This commercial variety is quite similar to the species, but it is very vigorous and tolerates temperatures of -15 °C for a short time. The growth of ˈOmbrellaˈ is umbrella-shaped and reaches a height of about 8 to 10 m.
- Albizia julibrissin ˈErnest Wilsonˈ: The variety ˈErnest Wilsonˈ differs from the species mainly in its much more pronounced frost hardiness. It can withstand temperatures down to about -23 °C. Due to the somewhat stocky growth with a height of 4 to 5 m, the shape is more rounded.
- Albizia julibrissin ˈSummer Chocolateˈ: With its unusual foliage, this commercial variety is very striking. The leaves, which are fresh green when they first appear, later turn red to chocolate brown and finally turn golden yellow in the fall. The Persian silk tree ˈSummer Chocolateˈ reaches a height of about 2 to 4 m 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 7 m and can withstand temperatures down to about -17 °C.
- Albizia julibrissin ˈEvey’s Prideˈ: The deep brown-wine red foliage of this variety adds exciting colour accents to any garden. It also grows up to 7 m high and bears bright pink flowers. Here, too, the winter hardiness is about -17 °C.
Tip: In addition to these varieties, there are also two varieties of silk tree. The Albizia julibrissin var. roseais somewhat more frost hardy, and Albizia julibrissin var. mollis is distinguished mainly by its densely hairy shoots. However, these varieties are rather rare in the trade in our part of the world.
Planting a Persian silk tree
It is very important that the Persian silk tree’s location is sunny, warm and protected from the wind. A south-facing wall is a very suitable option, for example. The silk tree does not make any specific demands on soil properties; however, permeability does plays an important role, which is why light, sandy soils are certainly to be preferred to heavy clay soil.
The Persian silk tree is most effective when planted as a solitary specimen. The best time for planting the silk tree is after the last frosts. Dig the planting hole generously and mix the excavated soil with sand or gravel to optimise permeability in clay-rich, heavy soils. After that, place the plant in the hole, press down and water.
Planting Persian silk tree in a container: The Albizia julibrissin varieties with a slightly lower growth height are particularly suitable as container plants. Especially in regions with harsher climates, this option is suitable for safe overwintering. To fill the large container, you should add a drainage layer of expanded clay at the bottom, then fill with a well-drained humus-rich substrate. For this purpose, for example, our Plantura Organic All Purpose Compost is ideal, which optimally supports the Persian silk tree in the growth phase with the already contained lime and magnesium fertiliser and organic fertiliser. The high humus content in our soil also causes a good water and nutrient supply, which makes the substrate ideal not only for container-grown plants but also for planting in the open ground.
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Caring for Persian silk tree care: pruning, fertilising and more
The Persian silk tree copes well with occasionally dry soils. It is only essential to provide additional water during dry periods to newly planted specimens. It is best to water container-grown Persian silk trees as soon as the top layer of substrate is completely dry, but no later than when the silk tree leaves fold or curl.
Optimal nutrient supply can be ensured by fertilising the silk tree in the spring. A high-quality slow-release fertiliser is particularly suitable for this purpose. Since the plant is not very salt tolerant, this should be done using a primarily organic fertiliser rather than a mineral one. For example, use our Plantura Flower Food, whose slow release of nutrients accommodates the sensitivities of the silk tree.
Especially when growing a Persian silk tree in a pot, annual pruning in the spring is useful. This allows you to adjust the shape as desired and somewhat limit the size. Freely planted specimens can be trained to shrubby growth by pruning. This mainly involves the removal of long, troublesome shoots.
Tip: Due to its good pruning tolerance, Persian silk tree can also be grown well as a bonsai.
Why is my Persian silk tree losing leaves? Leaf loss in Persian silk trees may be due to several reasons. It may be due to an excessively dark location or to improper care practices, such as too much or too little watering or fertilising. Furthermore, frost damage could lead to leaf drop. However, another cause may be the fungal wilt disease Fusarium oxysporum, which is a common and fatal disease for the Persian silk tree. The first visible symptoms are yellow, stunted, wilted leaves on the branches. Infestation with this fungus can be prevented mainly by ensuring an optimal location and proper care. At the very beginning, care should be taken to ensure that the purchased plant or seed used looks healthy and is not infested.
Is the Persian silk tree hardy?
The Persian silk tree’s winter hardiness is about -15 °C. As already described, the degree of frost hardiness varies somewhat from variety to variety. In milder, warm-weather locations, outdoor planting can certainly work with appropriate protective measures. Especially in the younger years, it is essential to provide the tree with winter protection – frost hardiness increases somewhat later. In cooler regions with harsher winters, opt for varieties with higher frost tolerance. Container planting with largely frost-free and relatively dry overwintering is possibly the safer option here. To avoid damage due to the cold, outdoor locations should always be sheltered and sunny.
For protection outdoors, the trunk can be wrapped with cold insulation, for example, raffia, and the root plate should be covered with a thick layer of mulch.
Propagating the Persian silk tree
One very reliable method of propagating the mimosa tree is via cuttings in early summer. For this purpose, it is best to take new shoots as close as possible to the base of the plant, with the leaves removed in the lower part. They are then put in pots with a constantly moist growing medium and placed in a bright place with an ambient temperature of about 25 °C. Propagation by root cuttings also works well.
Propagating the Persian silk tree by seed also works quite smoothly and quickly. It should be noted that the seeds are subject to mechanical inhibition of germination caused by the seed coat. This can be most easily broken by treating them with hot water. In this process, the seeds are poured into a small vessel with water at about 90 °C and left in it overnight. The seeds are then placed in planting trays with potting soil and at most lightly covered with it. They must now be kept constantly moist and put in a bright place. The optimum germination temperature is between 20 and 25 °C. If the seeds have been treated with hot water, the first seedlings will show after about 10 to 14 days.
Is Albizia julibrissin poisonous?
The poisonous parts of the Persian silk tree are the fruits and seeds. Be sure to keep them away from small children and animals to prevent consumption. The sap and leaves of the silk tree are harmless – they do not contain toxins. No irritation or other reactions are expected from skin contact with Albizia julibrissin.
Particularly in view of the rising temperatures and increasing drought, the Persian silk tree could also play a greater role here in the future as a so-called climate tree.