Silk Tree: Care, Flowering & Toxicity

The delicate leaves and striking flowers of the silk tree, also known as the sleeping tree, make it difficult to deny its direct relationship with the mimosa.

The low distribution of the plant in Central European garden culture is mainly due to the fact that the silk tree (Albizia julibrissin) is usually not sufficiently hardy. How you can still admire the decorative silk acacia in your garden and which varieties Albizia julibrissin You can find out which ones are best suited for this in this article.

Silk tree: flowering, origin and characteristics

The silk tree is known under the synonym sleeping tree because of its leaves, which it folds up overnight or when it is dry. In Chinese medicine, the bark of the tree is processed into sedatives, which gives the synonym additional meaning. The plant was called silk acacia because of its close relationship and its very similar appearance to the acacias (Acacia) named. These belong like the mimosas (Mimosa) in the same subfamily as the silk tree, namely the mimosa family (Mimosoideae). They are all classified in the legume family (Fabaceae). Persian sleeping tree, Japanese silk tree and Chinese silk tree are other synonyms that describe the same plant and are based on their respective distribution areas. The original home of the silk acacia is southern Asia. The sleeping tree is now particularly widespread in some countries in Asia, but also in South Africa and parts of South America. The plant shows invasive spreading potential, but not here because it is too cold here.

Depending on the region and climatic conditions, the deciduous plant grows as a shrub or tree, reaching a height of 6 to 8 m under optimal conditions. The silk tree forms an umbrella-shaped crown and, due to the frequent frost damage, usually grows in a multi-stemmed and shrub-like manner in Central Europe.

The alternate leaf fronds are bi-pinnate and are around 20 to 30 cm long. A special feature of the perennial plant is that the leaflets fold up at night and when it is dry. From a certain age and in warm locations, the silk tree develops flowers in mid-summer and thin ones later, even in Central Europe legumes with 8 to 12 seeds. The fragrant, hermaphrodite flowers of the sleeping tree are clustered together in head-shaped inflorescences characterize the appearance of the plant with its pink or white, long stamens from July to August.

Since the silk tree is only partially hardy depending on the variety and often requires protection at the beginning, planting it in a bucket is also suitable in this case. Due to the brittle wood and the thin, sensitive bark, the plant is often damaged in storms. It usually only lives between 10 and 20 years and is therefore not very long-lived.

Is the silk tree bee friendly? Although the exotic flowers also attract insects with their delicate scent, the silk tree is not a great asset for native bees, for example.

The most beautiful varieties

The different silk tree varieties differ, among other things, in their degree of frost hardiness. This should be taken into account if the future location of the plant is not in a warm region. We describe these and other characteristics of the varieties below.

• Albizia julibrissin “Ombrella”: This commercially available variety is quite similar to the species, but it is very vigorous and can tolerate temperatures of -15 °C for short periods. The growth of “Ombrella” is umbrella-shaped and reaches a height of around 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 around -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: This commercially available variety attracts everyone's attention thanks to its unusual foliage. The leaves, which initially sprout as fresh green, later turn reddish-chocolate brown and finally golden yellow in autumn. The silk tree “Summer Chocolate” reaches a height of around 2 to 4 m and is hardy down to around -17 °C.

• Albizia julibrissin ˈPendulaˈ: The special feature of this variety is the arched, overhanging shoots with pink flowers. It can reach a height of up to 7 m and can withstand temperatures of around -17 °C.
• Albizia julibrissin “Evey’s Pride”: The deep brownish-wine-red foliage of this variety creates exciting colorful accents in any garden. It also grows up to 7 m high and bears bright pink flowers. Here too, winter hardiness is around -17 °C.

Tip: In addition to the varieties, there are two varieties of the silk tree. There is Albizia julibrissin var. roseadescribed as somewhat more frost hardy than the species and Albizia julibrissin var. mollis differs primarily in its densely hairy shoots. However, these varieties are rarely available commercially here.

Plant a sleeping tree

The location of the silk tree should definitely be sunny, warm and protected from the wind. So, for example, a south facade is very suitable. The sleeping tree does not place any specific demands on the soil properties - but permeability is important plays an important role, which is why light, sandy soils are definitely preferred over heavy clay soils should.

The best effect of the sleeping tree is achieved by planting it as a solitary plant. The optimal time to plant the silk tree is after the last frosts. The planting hole should be dug generously and, in the case of clay-rich, heavy soils, the excavation should be mixed with sand or gravel to optimize permeability. The plant is then placed in the hole, pressed down and watered.

Planting a silk tree in a pot: Just those Albizia julibrissin-Varieties with slightly lower growth heights can be used well as potted plants. This option is particularly suitable for safe wintering in regions with a harsher climate. To fill the large bucket, a drainage layer of expanded clay at the bottom and a well-drained, humus-rich substrate should be used. Ours, for example, is suitable for this Plantura organic universal soil ideal, which optimally supports the silk tree in the growth phase with the lime and magnesium fertilizer already contained as well as the organic fertilizer. The high humus content in our soil also ensures a good supply of water and nutrients, which is why the substrate is ideal not only for the pot, but also for planting outdoors.

Silk tree care: cutting, fertilizing, etc.

The silk acacia copes well with occasionally dry soils. Only new plantings should definitely be supplied with additional water during dry periods. It is best to water the silk tree in the pot as soon as the top layer of substrate is completely dry is, but at the latest when the leaves of the sleeping tree fold up or even during the day roll up.

The optimal supply of nutrients can be ensured by fertilizing the silk tree in spring. A high-quality long-term fertilizer is particularly suitable for this. Since the plant is not very salt-tolerant, a primarily organic fertilizer should be used instead of a mineral one. For example, use ours Plantura organic flower fertilizer, whose slow nutrient release suits the sensitivities of the silk tree.

Particularly when growing the silk tree in a bucket, annual pruning in spring makes sense. This allows you to adjust the shape as desired and limit the size somewhat. Freely planted specimens can be trained into a shrub-like growth by pruning. Mainly long, annoying shoots should be removed.

Tip: Due to its good pruning tolerance, the silk tree can also be grown as a bonsai.

Why is my silk tree shedding leaves? If your silk tree is shedding leaves, there can be several reasons. It can be due to a location that is too dark or due to incorrect care measures, such as too much or too little watering or fertilizing. Furthermore, frost damage could lead to leaf drop. However, another cause can also be fungal wilt disease Fusarium oxysporum which is a common and fatal disease for the silk tree. The first visible symptoms are yellowish, stunted, wilted leaves on the branches. Infestation with this fungus can be prevented primarily through the optimal location and proper care. Right from the start, you should make sure that the plant you purchase or the seeds you use look healthy and are not infected.

Is the silk tree hardy?

The winter hardiness of the silk tree is around -15 °C. As already described, the degree of frost hardiness varies somewhat from variety to variety. In milder, warmer locations, outdoor planting with appropriate protective measures can definitely work. Winter protection should not be foregone, especially in the younger years, as the frost hardiness increases somewhat later. In cooler regions with harsher winters, varieties with higher frost tolerance should be used. Planting in a container with a largely frost-free and relatively dry winter may be the safer option. To avoid cold damage, outdoor locations should always be protected and sunny.

To protect it outdoors, the trunk can be wrapped with cold insulation, for example made of raffia, and the root plate should be covered with a thick layer of mulch.

Propagation of silk acacia

A fairly reliable method for propagating the silk tree is via cuttings in early summer. The best way to do this is to take new shoots as close as possible to the base of the plant and remove the leaves in the lower area. They are then placed in pots with constantly moist growing soil and placed in a bright place with an ambient temperature of around 25 °C. Propagation also works well with root cuttings.

But propagating the sleeping tree using seeds also works quite easily and quickly. The only thing to remember is that the seeds are subject to mechanical germination inhibition caused by the seed coat. The easiest way to break this is with hot water treatment. The seeds are poured into a small container with water at around 90 °C and left there overnight. The seeds are then placed in planting trays with potting soil and only lightly covered with it. They must now be kept constantly moist and also placed in a bright place. The best germination temperature is between 20 and 25 °C. If the seeds were treated with hot water, the first seedlings will appear after about 10 to 14 days.

Is Albizia poisonous?

Poisonous parts of the silk tree are the fruits and seeds. They should be kept away from small children and animals to prevent consumption. The sap and leaves of the tree are harmless - they do not contain any toxins. No irritation or other reactions are to be expected when skin comes into contact with silk acacia.

Especially in view of the rising temperatures and increasing drought, the silk tree could play a larger role in our future as a so-called climate tree. What exactly Climate trees You can find out what they are and what they include in our special article.