<em>Albizia</em>: planting, pruning and care

Botany

Albizia are deciduous trees and bushes prized for their silky inflorescences and their finely divided foliage, as delicate as mimosa! The species most commonly cultivated is Albizia julibrissin. It is thought to originate from Persia (Iran) and parts of Asia (Asia Minor, Himalaya, Bhutan, China, Japan…). It has naturalised in several regions of the world and has become invasive 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 locations 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 18th century. Its species name, julibrissin, would derive from Persian and mean “silk flower”. This idea is reflected in its vernacular name Silk tree and refers to its very soft, silky flowers. In French it is also called Mimosa de Constantinople, and it is indeed very close to mimosa. Scientifically, it is sometimes placed in the genus Paraserianthes (synonym).

Albizia belongs to the family Fabaceae, as do beans, peas, wisteria, clovers and lupin… This is one of the most important families economically, as it includes many food plants. These plants have the particularity of not needing nitrogen fertiliser, since their roots, by associating with bacteria, manage to 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 under optimal conditions. Albizia has a superb structure: it forms a fairly spreading shape with very horizontal branches, allowing it to reach 5 to 6 metres in spread. With its flattened crown, it has a true parasol habit… It is a perfect tree for shading! Its bark is grey, smooth, developing vertical striations as the tree ages.

Albizia flowers in midsummer, from mid-June–early July and into August–September. It then produces a striking flowering, in tassels or pom-poms gathered in terminal clusters. Each flower is borne on a long peduncle and measures between two and four centimetres in diameter. The flowers have very short, 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 and give the very soft appearance that earned the plant its name Silk tree. They are white at the base and vivid pink at the tip, creating a bright, original gradient. The flowers are hermaphrodite (they bear both male and female organs: stamens and pistil). Depending on the species, the form of the inflorescence can vary. For example, in Albizia lophantha it takes a bottlebrush form.

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

Albizia flowers are scented! They produce nectar and are melliferous: they attract bees and butterflies.

As Albizia is very close to mimosas and acacias, it also has very attractive foliage resembling theirs. Its foliage is light, not very dense, providing a dappled shade that shelters from sun while letting through good light. Albizia is a deciduous tree, dropping its leaves in autumn and producing new ones in spring. Leaves of Albizia julibrissin measure up to 45 centimetres long and up to 25 centimetres wide. They are alternate, arranged one after the other along branches.

Albizia foliage is extremely decorative. The leaves are twice-divided: they split into leaflets, which are themselves divided into leaflets… producing very small segments that make the foliage particularly light and feathery. Its very fine leaves somewhat recall fern foliage. They often consist of 8 to 12 pairs of leaflets, each further divided into 20 to 50 leafletlets. Number of leaflets and leafletlets may vary by variety, but it is always even: they are paripinnate. Leafletlets are oblong and measure up to one centimetre in length.

The leaves have a beautiful colour, a tender yet deep green. Albizia ‘Summer Chocolate’ stands out for its very dark, brown-purple foliage. Young leaves are first green, then darken with time. This variety offers a slightly less spectacular flowering than Albizia ‘Ombrella’, but it is spectacular for its foliage!

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

The leaflets have the peculiarity of being able to move: they fold at night and when light is low. It should be remembered that Albizia is very close to mimosa, including Mimosa pudica, a sensitive plant known for quickly folding its leaves when touched… Fabaceae species can easily fold their leaflets!

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

From September–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 ovate, dark brown seeds. Albizia may self-seed spontaneously. You can harvest the seeds and store them for sowing in spring.

Detail of pods of Albizia julibrissin (photo Ninjatacoshell) / Pods still on tree / Seeds contained in pods (photo Ninjatacoshell)

Albizia is not extremely hardy. It can tolerate −10 °C, even −15 °C for short periods if cold is not prolonged. Young plants are more sensitive to cold, so consider using fleece. Albizia grows quite quickly, especially in warm sunny climates, but it does not live very long, rarely exceeding 25 or 30 years.

What are the main varieties of Albizia?

Most popular varieties

Albizia julibrissin Ombrella

This albizia features beautiful soft green, finely divided foliage, and in midsummer it bears pink-and-white pompom flowers. 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 thanks to its very dark, brownish-purple foliage with superb tones. Before taking on this colour, its young leaves are first green, creating a lovely mix of colours with 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 preferable to grow Albizia in a mild climate. It will be perfect in gardens in southern France! During its first years it is relatively sensitive to cold. Once mature, it copes better with cold winters and can tolerate between -10 and -15 °C. In any case, plant it in full sun, in a warm, well‑exposed position. Choose a location sheltered from cold winds. Albizia ‘Summer Chocolate’ seems a little more fragile and delicate to grow than the ‘Ombrella’ variety.

Albizia is an undemanding plant that tolerates poor soils. It prefers a free‑draining, rather sandy soil. Avoid planting it in heavy clay. It really does not like waterlogged conditions or compacted soils. Do not hesitate to add draining materials at planting: pumice, gravel…

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

As Albizia is a tree that can become quite large, it is best not to plant it too close to a house or terrace. Its roots spread and sometimes produce suckers, which could damage the building. In any case, it is better to leave sufficient space for it to develop its crown freely, without requiring severe pruning.

If you live in a region with harsh winters, prefer to grow Albizia in a container (at least for the first few years) and move it under glass for the winter. Choose a large pot and add a drainage layer at the bottom. Plant the tree and water. You can then plant it in the ground after a few years.

We recommend planting Albizia in full sun and as a specimen! (photo Mihailo Grbic)

When to plant?

Preferably plant Albizia in spring, outside periods of frost.

How to plant Albizia?

It is generally recommended to plant Albizia as a specimen, to show it off better. However, if you plant several, leave at least seven metres between trees.

1. Place the root ball to soak in a tub of water. This will help the plant to establish.
2. Dig a planting hole two to three times the size of the root ball (at least 80 cm wide and deep). Do not hesitate to add gravel or pumice to improve drainage.
3. Remove the plant from the pot and gently loosen the roots.
4. Position your Albizia. The top of the root ball should be level with the soil surface.
5. Install a stake to keep the trunk straight.
6. Backfill with soil and firm down.
7. Water generously.

We recommend regular watering in the weeks following planting.

How to care for Albizia?

Albizia is drought-tolerant. Watering during the first year after planting is advisable, but once mature it will easily go without watering. During the first few years the tree is still delicate, so we recommend protecting it over winter with horticultural fleece. You can also lay mulch at the base of the tree: this will provide extra protection against cold and help keep soil cool. Albizia tolerates poor soils; its fertiliser or compost needs are fairly low. You can nevertheless add a little at the start of spring to encourage flowering.

Pruning Albizia is not always necessary. If you do wish to intervene, follow our advice: Albizia: when and how to prune it? For an older 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. 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 affected branches to prevent its spread.

Albizia is sometimes affected by coral disease. Bark becomes deformed and cracks, and orange pustules appear on the trunk and branches. If your tree is severely affected, we recommend felling it to prevent the disease spreading to other plants. Otherwise, cut and burn the affected twigs, apply a wound‑sealing mastic then spray a fungicidal treatment (Bordeaux mixture, sulphur…). Feel free to consult our advice sheet: How to prevent coral disease?

Also watch out for canker. These are fungi or bacterium that attack wood: branches dry out, bark cracks, calluses appear on the trunk or branches… We recommend removing damaged parts and applying a fungicidal treatment (Bordeaux mixture, sulphur…). As prevention, to avoid canker, make clean pruning cuts with disinfected tools and apply a wound‑sealing mastic.

Psyllids can attack albizia. These are insects that pierce the foliage and secrete honeydew. This can drip beneath the tree, staining anything underneath (cars, garden furniture…). Sometimes it is scale insects that attack albizia. The honeydew secreted by psyllids or scale can lead to the development of sooty mould (a black fungal coating that covers the foliage). To control psyllids and scale, you can spray black soap on the foliage. When grown under glass, albizia can also be attacked by red spider mites.

How to propagate Albizia?

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

Sowing Albizia

Prefer to sow seeds of botanical species Albizia julibrissin rather than seeds of varieties ‘Ombrella’ or ‘Summer Chocolate’, as latter may produce young plants different from original variety. Sow in late winter or early spring.

1. If you already have an Albizia in your garden, harvest seeds from tree, in pods, once they have turned brown and dry. Otherwise, you can order them.
2. Store seeds until early spring, in cool, dry place.
3. Before sowing, place seeds in hot water for at least 24 hours. This softens seed coat. You can also scarify them to aid germination, by nicking seed coat with a knife or sandpaper.
4. Fill pots with potting compost mixed with sand, then water.
5. Sow seeds, then cover with layer of potting compost (2–3 centimetres) and firm lightly.
6. Place pots in warm, sheltered spot (at least 18 °C), with good light.
7. Substrate should remain relatively moist until germination. Water regularly.
8. Pot on into individual pots when large enough to handle. You can grow them under cover first year and plant in garden following spring.

Sometimes Albizia self-seeds, and you may see small shoots at base of tree. Simply lift them to pot on.

Propagate Albizia by cuttings

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

1. Prepare a pot by filling with potting compost.
2. Take a shoot at least 10 centimetres long. Cut just below a node (point where leaves join stem). There must be no flowers on this branch. Also remove leaves at base of stem, if any, leaving only those at top of cutting.
3. Optionally dip base of cutting in rooting plant hormone.
4. Insert cutting into substrate and firm compost around stem.
5. We recommend covering pot with plastic bag to create humid environment.
6. Place pot in sheltered, bright position, but out of direct sun.
7. Open plastic bag regularly to ventilate and prevent fungal growth.
8. Water as soon as substrate starts to dry.

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

→ Find out more in our tutorial Taking a cutting of Albizia

Grafting Albizia

You can graft Albizia in summer by shield budding. Water rootstock and scion a few days before working.

1. Cut a branch from variety you wish to propagate.
2. Take a well-formed eye by incising bark for a few centimetres, avoiding taking wood (harder part at centre of branch).
3. Make a T-shaped cut on rootstock, carefully incising bark.
4. Place shield in cut of rootstock, and trim edges if they protrude.
5. Secure graft union with tie leaving bud visible. Bud should begin to develop following spring.

What to plant with Albizia?

Albizia is ideal when planted as a specimen. It has a magnificent silhouette, with branches that grow horizontally and give it a very spreading habit. We recommend placing it in the middle of a short grass meadow, possibly with garden furniture beneath (bench, table, deckchair…), to enjoy a relaxing moment in dappled shade.

You can also plant it in a row. If planted along a path, it will provide pleasant shade and lend a majestic aspect. Alternate Albizia varieties if desired, for example pairing pink-flowering varieties with others that produce white flowers… Or combine the green foliage of Albizia ‘Ombrella’ with the purple foliage of the ‘Summer Chocolate’ variety. The contrast effect is very attractive.

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

For an exotic feel, Albizia can also be paired with other plants of an exotic style. Choose, for example, castor oil plant, Trachycarpus palms or Phormium. In all cases, opt for plants that appreciate hot, dry conditions. You can create a Mediterranean-inspired garden by planting lavender, Jerusalem sage (Phlomis fruticosa), santolina or Gaura lindheimeri (its flowering will complement Albizia!). Also include climbing plants, which you can train on a pergola or against a wall: trumpet vine, wisteria, vine and bougainvillea. Create a dry garden with lush, cooling foliage and colourful flowering.

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 ideas for pairing with Albizia in our advice guide!

Did you know?

• Uses

Albizia wood can be used in joinery and cabinet-making. Its bark is used in Chinese medicine for its diuretic, digestive and anti-inflammatory properties. Its flowers can also be used to treat depression, insomnia and anxiety.