*Albizia*: plant, prune and maintain

Botany

The Albizias are deciduous trees and bushes appreciated for their silky inflorescences and finely dissected foliage, delicate like mimosa! The most commonly cultivated species is Albizia julibrissin. It is believed to be native to Persia (Iran) and Asia (Anatolia, Himalayas, Bhutan, China, Japan…). It has naturalised in several regions of the world and has become an invasive plant in the United States. The genus Albizia comprises between 140 and 150 species native to Africa, Australia, and Asia. They are found in tropical and subtropical regions, which explains why Albizia prefers warm situations and is only moderately hardy.

It was named Albizia in honour of Filipo degli Albizzi, a naturalist who brought the plant to Europe in the 18^th century. Its species name, julibrissin, is thought to derive from Persian, meaning “silk flower”. This idea is reflected in its vernacular name Silk tree, which alludes to its very soft silky flowers. In French, it is also called Constantinople mimosa, and it is true that it is very close to mimosa. As for its scientific name, it is sometimes classified under the genus Paraserianthes (synonym).

Albizia is part of the Fabaceae family, like beans, peas, wisteria, clovers, or lupins… It is one of the most economically important families, as it includes many food plants. These plants have the particularity of not needing nitrogen fertilisers, as their roots, by associating with bacteria, can fix atmospheric nitrogen. Albizia belongs to the subfamily Mimosoideae: it is very close to Mimosas and Acacias.

Albizia flowers

Albizia generally reaches between six and ten metres in height, but it can grow up to 15 metres tall under optimal conditions. Albizia has a superb architecture: it takes a rather spreading form, with very horizontal branches, allowing it to reach 5 to 6 metres in span. With its flattened crown, it has a true parasol habit… It is a perfect tree for shade! Its bark is grey, smooth, and forms vertical stripes as the tree ages.

Albizia flowers in mid-summer, from mid-June to early July, and until August-September. It then offers an original flowering, in feathery clusters or pom-poms, gathered in terminal clusters. Each flower is borne on a long peduncle (flowering stem) and measures between two and four centimetres in diameter. The flowers have very short and fused sepals and petals, with five lobes. It is the stamens, very long and numerous, that are impressive. They measure between two and four centimetres in length, giving this very soft appearance, which earns the plant its nickname Silk tree. They are white at the base and bright pink at the tip, creating an original, very bright gradient. The flowers are hermaphroditic (they bear both male and female organs: stamens and pistil). Depending on the species, the shape of the inflorescence can vary. Thus, in Albizia lophantha, it takes on a “bottlebrush” shape.

The flowers of Albizia julibrissin take the form of white and bright pink pom-poms, which stand out beautifully against the green foliage. They resemble the flowers of calliandra. Depending on the different species and varieties, the flowers can also be entirely white, as in Albizia julibrissin ‘Alba’, or cream white, as in Albizia amara, or even yellow-green. Sometimes they take on a very bright hue, almost red, as in Albizia ‘Rouge de Tuilière’. When they are white or cream, the flowers of Albizia have a very light and delicate quality.

The flowers of Albizia are fragrant! They produce nectar and are melliferous: they attract bees and butterflies.

As Albizia is very close to Mimosas and Acacias, it also has very beautiful foliage, which resembles theirs. Its foliage is light, not very dense, thus providing dappled shade that shelters from the sun while allowing good light to pass through. Albizia is a deciduous tree, shedding its leaves in autumn and producing new ones in spring. The leaves of Albizia julibrissin can measure up to 45 centimetres in length and up to 25 centimetres in width. They are alternate, arranged one after the other on the branches.

The foliage of Albizia is extremely decorative. The leaves are twice dissected: they divide into leaflets, which are themselves divided into leaflets… creating very small segments that make the foliage particularly light and feathery! Its very fine leaves somewhat resemble fern foliage. They often consist of 8 to 12 pairs of leaflets, each subdivided into 20 to 50 leaflets. The number of leaflets and leaflets can vary depending on the varieties, but it is always even: they are said to be paripinnate. The leaflets are oblong and can measure up to one centimetre in length.

The leaves have a very beautiful colour, a tender yet deep green at the same time. The Albizia ‘Summer Chocolate’ stands out for its very dark, purplish-brown foliage. Its young leaves are initially green, then darken over time. This variety offers a somewhat less interesting flowering than the Albizia ‘Ombrella’, but it is spectacular for its foliage!

The foliage of albizia: detail of a leaf of Albizia julibrissin / the purplish foliage of Albizia ‘Summer Chocolate’ / Albizia julibrissin (photo Jean-Pol GRANDMONT)

The leaflets have the particularity of being able to move: they fold at night and when light levels are low. It should not be forgotten that Albizia is very close to mimosa, including Mimosa pudica, a sensitive plant known for quickly folding its leaves when touched… The Fabaceae are plants that can easily fold their leaflets!

The roots of Albizia, like those of other Fabaceae, have the ability to fix atmospheric nitrogen by associating with bacteria of the genus Rhizobium. The roots form nodosities, which allow the bacteria to live in symbiosis with the plant, providing it with nitrogen in exchange for carbon compounds from photosynthesis.

From September to October, Albizia produces long, flattened pods, first green then brown. They measure between 10 and 20 centimetres in length and contain between five and fifteen oval, dark brown seeds. Albizia can sometimes self-seed. You can collect the seeds and store them for sowing in spring.

Detail of the pods of Albizia julibrissin (photo Ninjatacoshell) / The pods still on the tree / The seeds contained in the pods (photo Ninjatacoshell)

Albizia is not extremely hardy. It can withstand -10 °C, even -15 °C, for a short period, provided the cold does not last. Care should be taken with young plants, which are more sensitive to cold, and do not hesitate to install a winter cover. Albizia is a tree that grows quite quickly, especially in a warm and sunny climate, but it does not live very long, rarely exceeding 25 or 30 years.

What are the main varieties of Albizia?

The most popular varieties

Albizia julibrissin Ombrella

This albizia offers beautiful tender green foliage, highly divided, and it bears pompom flowers in pink and white in mid-summer. It is perfect as a shade tree!

• Flowering time August, September
• Height at maturity 5 m

See the product sheet

Albizzia julibrissin Summer Chocolate

An original variety with very dark, purplish-brown foliage, featuring stunning nuances. Before taking on this shade, its young leaves are initially green, creating a beautiful mix of colours with the older leaves.

• Flowering time August, September
• Height at maturity 4,50 m

See the product sheet

When to plant Albizia?

Where to plant?

It is best to grow Albizia in a mild climate. It will be perfect for gardens in the south of France! During the first few years, it is relatively sensitive to cold. Once mature, it can more easily withstand cold winters, tolerating temperatures between -10 and -15 °C. In any case, plant it in full sun, in a warm, well-exposed location. Choose a spot sheltered from cold winds. Albizia ‘Summer Chocolate’ seems a bit more fragile and delicate to grow than the ‘Ombrella’ variety.

Albizia is a low-maintenance plant that tolerates poor soils. It thrives in well-draining, sandy soil. Avoid planting it in clayey ground. It really dislikes stagnant moisture and overly compacted soils. Don’t hesitate to add drainage materials when planting: pumice, gravel…

Albizia tolerates salty soils quite well: it will easily adapt if your garden is by the sea. It also withstands calcareous soils.

As Albizia is a tree that can grow quite large, it is best not to plant it too close to a house or terrace. Its roots spread out and can sometimes produce suckers, which could damage the building. In any case, it is better to give it enough space to develop its crown freely, without needing excessive pruning.

If you live in an area with a harsh climate, it is advisable to plant Albizia in a pot (at least for the first few years) and bring it indoors under glass for the winter. Choose a large pot and place a drainage layer at the bottom. Plant the tree and water it. You may eventually plant it in the ground after a few years.

We recommend planting Albizia in full sun and in isolation! (photo Mihailo Grbic)

When to plant?

Preferably plant Albizia in spring, outside of frost periods.

How to plant Albizia?

It is generally recommended to plant Albizia in isolation, to better showcase it. However, if you are planting several, maintain at least seven metres of distance between the trees.

1. Soak the root ball in a basin filled with water. This will help the plant establish itself.
2. Dig a planting hole two to three times the size of the root ball (at least 80 cm wide and deep). Don’t hesitate to add gravel or pumice to improve drainage.
3. Remove the plant from the pot and gently untangle the roots.
4. Place your Albizia. The top of the root ball should be level with the soil.
5. Install a stake to keep the trunk upright.
6. Replace the soil and firm it down.
7. Water generously.

We recommend regularly watering in the weeks following planting.

How to care for Albizia?

Albizia is drought-resistant. It is advisable to water it during the year of planting, but once mature, it can easily do without watering. During the first few years, the tree is still fragile, which is why we recommend protecting it for winter with a winter cover. You can also apply mulch at the base of the tree: this will provide additional protection against the cold and keep the soil cool. Albizia is suited to poor soils, and its fertiliser or compost needs are quite low. However, you can add a little in early spring to encourage flowering.

Pruning Albizia is not necessarily useful. If you do wish to intervene, follow our advice: Albizia: when and how to prune it? For an old specimen, read our article How to rejuvenate an old albizia or silk tree.

As for diseases, albizia can be affected by fusarium wilt, caused by a fungus. The leaves wilt and discolour but tend to remain on the tree. Like many fungal diseases, it is favoured by a combination of heat and humidity. Unfortunately, there is no treatment. Cut and burn the affected branches to prevent its spread.

Albizia is sometimes affected by coral disease. The bark deforms and splits, and orange pustules appear on the trunk and branches. If your tree is severely affected, we recommend felling it to prevent the disease from contaminating other plants. Otherwise, cut and burn the affected shoots, apply a healing paste, and then spray a fungicidal treatment (Bordeaux mixture, sulphur…). Feel free to consult our advice sheet: How to prevent coral disease?

Be also cautious of canker. This involves fungi or bacteria that attack the wood: branches dry out, the bark splits, and calluses appear on the trunk or branches… We advise removing the damaged parts and applying a fungicide (Bordeaux mixture, sulphur…). As a preventive measure to avoid canker, carry out clean pruning with disinfected tools and apply healing paste.

Psyllids can attack albizia. These are insects that pierce the foliage and secrete honeydew. This may drip down under the tree, staining everything below (cars, garden furniture…). Sometimes, scale insects also target albizia. The honeydew secreted by psyllids or scale insects may lead to the appearance of sooty mould (a black substance caused by a fungus that covers the foliage). To combat psyllids and scale insects, you can treat by spraying black soap on the foliage. When grown in a greenhouse, albizia can also be attacked by red spider mites.

How to propagate Albizia?

To propagate Albizia, we recommend sowing, which is easier to succeed than propagation by cuttings or grafting.

Sowing Albizia

It is preferable to sow seeds of the botanical species Albizia julibrissin rather than those of the varieties ‘Ombrella’ or ‘Summer Chocolate’, as the latter may produce young plants different from the original variety. You can sow at the end of winter or the beginning of spring.

1. If you already have an Albizia in your garden, collect the seeds present on the tree, in the pods, once they have turned brown and dry. Otherwise, you can order them.
2. Store the seeds until early spring, in a cool, dry place.
3. Before sowing, place the seeds in hot water for at least 24 hours. This helps to soften the seed coat. You can also scarify them to facilitate germination by nicking their coat with a knife or sandpaper.
4. Fill pots with a mixture of potting soil and sand, then water.
5. Sow the seeds, then cover with a layer of potting soil (two to three centimetres thick) and lightly firm down.
6. Place them in a warm, sheltered location (at least 18 °C), with good light.
7. The substrate should remain relatively moist until germination. Water regularly.
8. Transplant them into individual pots when they are large enough to handle. You can grow them under cover for the first year and plant them in the garden the following spring.

Sometimes, Albizia self-seeds, and you may see small shoots at the base of the tree. You can simply collect them to transplant.

Taking Cuttings of Albizia

In mid-summer, you can take semi-woody cuttings. Propagation by cuttings of Albizia is more delicate than sowing, but it allows for faithful reproduction of horticultural varieties.

1. Prepare a pot by filling it with potting soil.
2. Take a shoot at least 10 centimetres long. Cut just below a node (the point where leaves attach to the stem). There should be no flowers on this branch. Also, remove any leaves at the base of the stem, if present, to keep just a few at the top of the cutting.
3. Optionally dip the base of the cutting in rooting hormone.
4. Plant it in the substrate and firm the soil around the stem.
5. We recommend covering the pot with a plastic bag to create a humid atmosphere.
6. Place the pot in a sheltered, bright location, but out of direct sunlight.
7. Open the plastic bag regularly to air it out and prevent the development of mould.
8. Remember to water as soon as the substrate begins to dry out.

It is also possible to take root cuttings in winter, around February. Scrape the soil around the tree to collect some roots (2 to 3 centimetres in diameter). Cut fragments at least 10 centimetres long. Prepare pots with potting soil and plant the roots in them. Water.

→ Learn more in our tutorial How to Take a Cutting of Albizia

Grafting Albizia

You can graft Albizia in summer, by budding. Water the rootstock and the scion a few days before you intervene.

1. Cut a branch from the variety you wish to propagate.
2. Take a well-formed bud by making an incision in the bark a few centimetres long, avoiding taking any wood (the harder part located at the centre of the branch).
3. Make a T-shaped cut on the rootstock by carefully incising the bark.
4. Place the bud in the cut of the rootstock, and trim the edges if they protrude.
5. Wrap the grafting point, leaving the bud exposed. It should start to develop the following spring.

How to pair Albizia?

Albizia is ideal when planted in isolation. It has a magnificent silhouette, with branches that grow horizontally, giving it a very spreading habit. We recommend placing it in the middle of a short grass meadow, possibly with garden furniture underneath (bench, table, deck chair…) to enjoy a moment of relaxation under dappled shade.

You can also install it in alignment. If planted along a path, it will beautifully shade it while adding a majestic touch. You might alternate varieties of Albizia, for example, by pairing pink-flowering varieties with those that offer white flowers… Or by combining the green foliage of Albizia ‘Ombrella’ with the purplish foliage of the variety ‘Summer Chocolate’. You will achieve a lovely contrast effect.

To pair with albizia, we recommend choosing other plants in similar tones. Prefer large divided foliage, such as wisteria or ferns, to create a lush-looking garden. Also opt for flowers in pink or mauve tones: Gaura lindheimeri, oleander, Lagerstroemia indica…

For a tropical effect, Albizia can also be paired with other exotic-style plants. Choose, for example, castor oil plant, Trachycarpus palms, or Phormium. In any case, opt for plants that enjoy warm and dry conditions. You can create a Mediterranean-inspired garden by installing lavenders, Jerusalem sage (Phlomis fruticosa), santolines, or Gaura lindheimeri (its flowering will harmonise with the Albizia!). Also focus on climbing plants, which you can direct over a pergola or against a wall: trumpet vine, wisteria, vine, and bougainvillea. Create a dry garden with lush, refreshing foliage and colourful flowers.

Albizia can find its place in an exotic-style garden! Albizia julibrissin ‘Ombrella’ (photo wlcutler), Trachycarpus fortunei, Nerium oleander (photo Tubifex), Campsis radicans (photo Dinesh Valke)

→ Discover more pairing ideas with Albizia in our advice sheet!

Did you know?

• Uses

Wood of Albizia can be used in carpentry and cabinetmaking. Its bark is used in Chinese medicine for its diuretic, digestive, and anti-inflammatory properties. Its flowers can also be used to treat issues of depression, insomnia, and anxiety.