The genus Albizia consists of small trees, common in Asia, Europe, Australia and North America; in Italy the only species that is commonly cultivated is Albizia julibrissin, also called acacia or mimosa ci Costantinopoli, a species widespread all over the globe, considered an invasive species in some areas. The albizia is a small tree, which normally does not exceed 5-6 meters in height, producing a thin erect stem on which a thick, very wide and dense semi-spherical crown expands; the leaves are large, pinnate, made up of small oval leaflets, fall in autumn, and reappear in early spring.
In late spring albizie produce a spectacular flowering, their tiny flowers, characterized by having the corolla much shorter than the stamens, are gathered in tight bunches, which give rise to species of pink and yellow pom-poms, in the shape of a half ball. Once these trees were often confused with mimosas or even with acacias, with which they share many characteristics; in fact they have a certain kinship with both genera, being part of the fabaceae (leguminous).
As with all legumes, even the seeds of albizie are enclosed in thin siliques, such as those of beans or of the cercis, or long pods, which remain long on the tree. The seeds of albizia they are generally fertile, and it is not uncommon to find small specimens of albizia born from seed at the feet of adult trees.
How to grow albizia
These small, very decorative trees are completely rustic in Italy, and it is probably also for this reason that they have had great success in the past in cultivation. They are positioned in well-lit areas, with at least a few hours of direct sunlight every day.
They bear frost very well, up to about -25 ° C, but also drought, wind, pollution, saltiness; in many Italian cities they have been used in street furniture.
The adult specimens, at home for at least a few years, are self-sufficient trees, which do not require any care, as they are satisfied with the rainfall water, and form a well-balanced and orderly foliage, which does not need training. The newly planted saplings may need summer watering, certainly at the time of implantation, but also later in case of prolonged drought.
We recall that it is leguminous, therefore in general it is not necessary to supply fertilizers based on nitrogen, since the roots of the tree live in symbiosis with nitrogen-fixing bacteria, which make nitrogen present in the air available to the plant. At the end of winter it is advisable to remove the thinnest or weather-damaged branches from the youngest specimens.
We live in an area characterized by a strongly hot and dry climate in summer, it is advisable to place the albizia specimens in a semi-shaded area, especially during the hottest hours of the day; if instead we live in a region that has a decidedly very cold winter climate, for very long periods of time, with frosts also towards the end of winter, then it is good to place the albizia in an area slightly protected from the cold wind.
Recall that this is a tree that is not very large, but that produces a very enlarged crown, for this reason, at the time of the plant, remember to place the tree where it can easily develop its foliage, then at least a few meters away from other trees or buildings.
At the end of winter it is customary to fertilize the plants in bloom, burying small quantities of mature manure around the stem.
Albizie and psylla
Some years ago most of the albizie planted in the gardens and in the flower beds of most of the regions of the Po valley were attacked by a small insect, belonging to the genus psylla, which attacked such trees massively and heavily, so as to kill them a good percentage; only the most robust and healthy trees, and the best cared for, which received watering and shade in the summer, were saved.
Most likely an attack so massive and sudden, occurring only on a variety of plants (or at least, only on the albizie became very evident), was caused by various concomitant events; the first of which probably due to an anomalous spread of these insects, starting from some wine areas of Trentino. In addition to this it was a period that lasted some years, with particularly long winters, with late frosts, and very dry summers, accompanied by springs and autumn that were not too rainy; all these elements together contributed to the immoderate proliferation of the psylle, and to the total incapacity of the albizie to defend itself from the parasites.
Albizia in short
First name: Albizia julibrissin, albizzia julibrissin, acacia or mimosa of Constantinople
Plant type: Shrub
Use: In hedges or isolated plant
Height at maturity: 5-6 meters
Growth rate: slow
Diseases and pests: Psylla, cochineal
Temperature: Withstands summer heat and winter cold (even at temperatures below 00 C)
Pests and diseases
In the following years it seems that these infestations have not been verified; in any case, if your whiteness shows obvious signs of pest infestation, with large amounts of honeydew falling from the top, with flying insects evident on the underside of the leaves, and many suffering leaves that turn yellow in the middle of summer, it is good to place immediately remedy. Unfortunately, psylla is a difficult insect to eradicate with common insecticides, as it covers the eggs and larvae of a waxy substance, which keeps them stuck to the leaves; for this reason, before using an insecticide, the plant is "washed" using water and potassium soap, or soft soap, in order to expose all the stages of the insect to the insecticide. Any insecticide intervention in the garden is practiced only and exclusively when there are no flowers in full development, otherwise the treatments become harmful even for useful insects; and this happens also for the treatments practiced with products used in organic farming.
Plant the albizia in autumn or spring, but choose spring if you live in the winter where it is stiff, as you risk seeing the plant die due to winter frosts.
It is preferable that the cultivation of albizia takes place in open ground and not in pots, especially in regions with a hot-humid climate. The soil must be draining and the place must be sunny because the albizia loves light. If you live in an area where winter is rather harsh, choose a location sheltered from cold winds.
You can find on the market some plants to buy both in the pots, both in clods and in the bare root. Choose the right place and dig a hole about 60 cm in diameter and depth. If the soil is poor, provide sufficient humus. Remember that the albizia reaches considerable dimensions, so place the plant at least 5 m away from the other trees.
In the growth phase, up to two years, the albizia is particularly sensitive to temperature changes and frosts, so in the winter period made a mulch around the base of the plant. And if the temperatures are very cold it is advisable to cover the foliage with a cloth. During the summer, in the first two years, it is advisable to protect the top to prevent the young shoots from being burned by the sun.
Albizia pruning is necessary during the training period, which takes place at the beginning of spring (generally in March). Pruning will become increasingly rare in the adult tree.
There training pruningaims to select and promote the growth of the most robust stem, which will become the trunk of the plant. Choose the straightest and most robust stem; also do not forget to provide the plant with two rather solid stakes to favor the development of an erect stem, and to prevent the plant from being damaged by the wind. Eliminate the other weaker stems and the side branches. Let the stem grow and, when it reaches the height that you consider suitable, cut the top and leave the lateral branches that will develop spontaneously.
To favor the formation of a hemispherical crown, eliminate the vertically growing branches and the branches that cross or overlap: you will gradually notice that your whiteness will take on an umbrella shape.
If the albizia reaches very large dimensions in width, do not be too severe with the cuts since the plant reacts badly, so intervene by performing interventions on several consecutive years instead of eliminating too many branches at once. Make the cuts in the summer so that there is no difficulty in healing.
The cultivation of albizia
Ground: Calcareous, sandy, rocky
Cleaning / Pruning: Training pruning. Not necessary pruning in the adult plant: eliminate only the dry or ruined twigs, or the shoots that develop near the trunk.
Water needs: poor
Soil moisture: Draining
Fertilization: Late winter-early spring to encourage flowering.
Multiplication: Sowing, cutting
Watering and fertilizing
If you grow albizia in pots, remember to water it regularly. While the plant in the ground needs to be watered only if the summer is particularly hot and dry: you will find that the plant needs water with yellowed leaves due to excessive drought.
Albizia does not need periodic fertilization, but to improve flowering you can place mature manure around the stem at the end of winter or give fertilizer in the spring.
Propagation of Albizia
Albizia can be reproduced by sowing, rooted sucker and cuttings, but in this latter case the chances of success are limited. Sowing generally takes place spontaneously, and in this case the albizia can even become a weed.
There reproduction by sowing It is the most economical way to have numerous seedlings. However, the same plant variety is not always obtained from the seeds, so you'll have to graft it if you have preferences. If you already cultivate the albizia and intend to get young plants from the seeds, recover the seeds at the end of autumn when they are now dried, but before they are dispersed due to the opening of the pods. The seeds must be stored in the dark, in a cool, dry place.
There sowing will be carried out the following year, in late spring, when the temperature has reached at least 20 0C-25 0C. To facilitate reproduction, leave the seeds in water for a few days before sowing.
The reproduction by cuttings takes place in the summer period using semi-woody twigs, but this method is difficult to succeed.
The Albizia calendar
Sowing: Spring (temperature between 20 ° C-25 ° C)
Planting: Spring or autumn (in the mild areas where frost is absent even in winter)
Flowering: July August