Albizia Bonsai: The Sleeping Silk Tree

TheConstantinople Acacia(Albizia julibrissin), often also called "Silk Tree" or "Gaggia," is a bonsai tree that brings a touch of exoticism and delicacy. Belonging to the Fabaceae (Leguminosae) family, it is distinguished by two unique features: its pink summer flowers in the shape of a soft, fragrant down, and its compound leaves that, thanks to a phenomenon called nictinastia, close in on themselves when the sun goes down or when touched, as if the plant were going to sleep. It is a fast-growing essence, ideal for those who like to see fast results.

Origin & species

Native to a wide belt from Iran to Japan, it was introduced to Europe in the 18th century by a Florentine naturalist who brought it from Constantinople (hence the common name). It is a deciduous tree that takes on an umbrella shape in nature. The "Summer Chocolate" variety, with bronze/purple leaves, is popular in bonsai for its color contrast, but is slightly more delicate than the green-type species.

Exposure and Microclimate

Albizia is a child of the sun. It loves warmth and bright light.
Place it in full sun for most of the year. Light is essential for flowering and for keeping the leaves (which tend to be large) an acceptable size.
In summer, if you live in torrid areas, a little shade in the middle hours will prevent the tender leaves from "drooping" excessively from transpiration, but do not deprive it of light, otherwise the branches will stretch out of proportion.

Watering

Needs regular water but cannot tolerate constant "wet feet."
Water thoroughly when the potting soil begins to dry on the surface. It drinks a lot in summer because of the large leaf area. However, reduce watering in late summer to encourage wood hardening before winter. If the leaves close during the day (and it is not night), the plant is telling you it is thirsty!

Water quality

It is not particularly fussy. Tap water is fine. As a legume, it is quite adaptable to different pHs, although it prefers neutral or slightly acidic soils.

Substrate

Drainage is critical, but it also needs nutrients to support fast growth.

• Recommended mix: 50 percent Akadama (for structure), 30 percent Pumice and 20 percent Humus or Universal Potting Soil.
• The addition of organic matter is important to retain needed moisture in the warm months, as Albizia suffers if the root ball dries out completely.

Repotting

This is done in late spring (May), when temperatures are stably warm and buds are swelling.
The root system is vigorous and fleshy. Repot young specimens every 2 years. When repotting you can shorten the thicker roots, but try not to disturb the central root ball too much. Use pots a little wider to accommodate horizontally expanding roots.

Fertilization

Watch out for nitrogen!
Like all leguminous plants, Albizia fixes atmospheric nitrogen. If you use fertilizers that are too nitrogen-fixing, you will have giant leaves, long internodes and zero flowers.
Use a balanced organic fertilizer (balanced NPK) in spring, and switch to one with high potassium (K) and phosphorus (P) before summer to stimulate flowers.

Flowering and fruiting

It blooms in midsummer (June-July) with pink/white inflorescences made of long silky stamens.
After the flowers, it produces long, flat pods (legumes) that contain seeds. In bonsai, these pods sap energy and are unsightly if left in quantity: remove them as soon as they form so as not to weaken the tree.

Structure pruning

This is done in late winter, before awakening.
The wood of the Albias is quite brittle and tends to break if bent badly, but cuts heal fairly well. Remove branches that grow vertically or cross the trunk. Since it tends to lose low branches if they do not get light, prune the apex firmly to give strength to the lower part.

Maintenance pruning

This is a fast-growing plant. During the growing season, shorten branches that stretch out of shape.
However, if you want flowers, remember that these are born on the year's growth (on the tips of new branches). If you keep topping everything until July, you will cut off the buds!

Stapling

This is done in spring on strong shoots that are not needed for flowering. Cimate to 2-3 leaves to keep the foliage compact. If the goal is structure and not flowers, staple regularly throughout the summer.

Binding & folding

The bark of the Albizia is thin and delicate; it marks very easily.
Apply wire in late spring to young branches that are still flexible. Protect the branch with crepe paper or raffia before putting the wire on. Check every 15 days: the branches swell quickly, and the wire will incarnate in no time.

Diseases and pests

• Psyllid (Acacia Psyllid): A small insect that attacks new shoots, deforming them.
• Cottonwood me alybug: It often lurks at branch forks.
• Fusarium: A vascular fungus that can strike if the soil does not drain well (causes sudden wilting of branches).

Winter & protection

It is deciduous and loses its leaves. It withstands moderate cold, but fears prolonged intense frosts, especially on the roots.
In northern Italy, protect the pot with mulch or store it in a cold greenhouse. Beware of late spring frosts that can burn delicate early shoots.

Annual calendar

• January-February: Rest, structure pruning.
• March-April: Reawakening, repotting (late spring).
• May-June: Fertilization (little nitrogen), selective stapling.
• July-August: Flowering (show!), heavy watering.
• September-October: Pod removal, PK fertilizer.
• November-December: Leaf drop, protection.

Useful products for this bonsai

• Hard Quality Akadama (For healthy roots)
• Fertilizer for Blooms (Low nitrogen for Albizia)
• Medium Scissors (For green pruning)
• Coppered aluminum wire (Gentle on bark)
• Healing putty (To protect brittle cuts)
• Earthworm humus (To enrich the substrate in summer)

Frequently Asked Questions about Albias

Why do the leaves close in the daytime?
If the leaves close while there is still light, the plant is either water stressed (thirsty) or suffering from excessive heat stroke. Water it immediately and put it in the shade for a few hours.

Is it the same as a Mimosa?
It is often called a "Mimosa," but the real Mimosa(Acacia dealbata) has yellow pellet flowers that bloom in February/March. Albizia has pink feathery flowers that bloom in summer. They are cousins (same family), but different plants.

Why doesn't it bloom?
The Albizia blooms at the tip of new branches produced in the year. If you keep pruning the branches to keep it in shape until summer, cut off the flowers. To see it bloom, you have to let it grow free (and somewhat disheveled) from May onward.