The bunches of mimosa or Acacia dealbata that we buy in March on the streets come from greenhouse cultivation where the mimosas are grown specifically for the production of cut flowers, but the mimosa is above all a beautiful garden plant that has no contraindications other than that of the climate. In fact, it can live outdoors in the olive tree area or for some varieties even in slightly colder areas; in fact, they are found in Liguria, Tuscany, Marche, in all the southern regions and in the microclimates of the great lakes of the north. Exceptionally, it can tolerate temperatures of -10/-12 degrees as long as they are for a short period.
A tree with a round crown
Acacia dealbata is an evergreen tree, native to Australia from where it was brought to Europe in 1824. If left in its natural state it forms a round crown 10/15 meters high, in the areas of origin trees of up to 25/30 meters have been reported. The bipinnate leaves are composed of very small leaflets that are soft to the touch and range in color from light green to glaucous depending on the variety. They have the unusual characteristic of closing during the night, on cold days or during strong storms. The flowers, which form a flower head, are small, gathered in glomerules, of a more or less accentuated yellow color and very fragrant. They are so numerous that when the plant is in full bloom it gives the impression of being a large yellow balloon.
Grafting plants for the garden
The common species reproduces easily from seed and in some areas such as the French Riviera, the Ligurian Riviera or the island of Elba it has become naturalized, occupying mainly the bottom of ravines or gullies where the soil is cooler, forming patches of small thickets. Its diffusion is due not only to the seed but above all to the suckers that form from the roots emerging even at a distance of several dozen meters from the mother plant, it has in fact a robust and very extensive root system.
Acacia dealbata does not live in calcareous soils.
In the garden, however, it is advisable to plant grafted varieties. These are smaller in size than the seed mimosa, have larger selected flowers, a more abundant flowering that goes from January to April depending on the variety and have foliage with brighter colors that go from deep green to glaucous. The color of the foliage is important because, being an evergreen, it is characterized differently in the garden near other plants and during flowering it creates a different contrast with the yellow of the flowers.
But the main reason that should make us prefer grafted plants is above all because these are grafted onto Acacia retinoides which allows the mimosa to live even in slightly calcareous soils.
It is in France, on the French Riviera that mimosa has found its greatest success and use. There it is used abundantly in gardens, parks and city avenues. In that region there are many nurserymen who have specialized in reproduction and research and this is the reason why several varieties on the market have French names. However, Italian nurserymen are not far behind and offer an excellent and diversified production. Nurseries specialized often in monoculture of Acacia are found on the Ligurian Riviera, in Tuscany in the area of Pistoia and Pescia and in recent years also in Sicily. The reproduction and cultivation of mimosa involve a long series of highly specialized operations and these nurseries have always been considered the ‘noble part’ of nursery gardening.
Species and cultivars
The species and cultivars are numerous but those actually available are no more than twenty. Below are the most important or the most curious.
With compound leaves
Acacia baileyana : large shrub or small, very elegant tree of 6/8 metres with small, short, silvery grey leaves, also native to Australia, it produces small flowers borne in sparse, elongated terminal panicles, the flowering is showy; many of the hybrids and cultivars existing today are the result of crosses between Acacia dealbata and Acacia baileyana .
Acacia baileyana ‘Purpurea’ : the new growth is reddish and the branches and the underside of the young leaves are also slightly purple.
A. dealbataobtained by grafting: this is the simple name given to this selection of Acacia dealbata, which grows strongly and has silvery foliage and is resistant to cold; the flowers are a little sparse.
A. dealbata ‘Gaulois’ : it is perhaps still one of the most beautiful in its late flowering in February/March; it has grey-green foliage and the plant grows strong even if it tends to string slightly, it is the variety most used for cut flowers.
A. dealbata ‘Mirandole’ : it is the most widespread in France where some nurseries and garden centers have given themselves this name; in fact, its origin is precisely on the French Riviera where this cultivar was isolated at Villa Mirandole in Cannes. It has beautiful gray-green foliage and early flowering with sparser flowers than the Gaulois and is quite rustic.
A. nivea : light yellow, almost white flowers, the plant grows strong and has beautiful deep green foliage but flowering is scarce and very late; rare to find.
A. dealbata ‘Rustica’ : this is the most recommended variety for planting in the garden and is also used planted in rows to create curtains of greenery; after A. dealbata from seed it is considered the most resistant to cold, it is of good shape, full, with bright green foliage and late flowering.
A. dealbata ‘Turner’ : similar to A. dealbata ‘Rustica’, it has a more compact habit, denser, more ash-coloured foliage and more abundant flowering with almost double flowers; a variety widely used for cut flowers.
A. dealbata ‘Virginia’ : rare variety, bright orange flowers; strangely some plants lose their orange colour as they age and year after year their flowers become more and more yellow; ultimately they resemble A. dealbata ‘Gaulois’; early flowering.
Acacia dealbata ‘Pendula’ or pendula mimosa: curious variety with drooping branches often grafted into a small tree. It can be planted close to a wall and the main branches supported with small clamps to create a geometric figure while the tips and secondary branches are left to hang freely; over time it can cover an entire wall with a fantastic effect.
With whole leaves
In some Acacias, what appear to be whole leaves are nothing more than the leaf stalk that has assumed an enlarged shape and which in fact functions as a leaf. These pseudoleaves are called phyllodes by botanists.
Acacia retinoides : this is the botanical name of the acacia used as a rootstock for all varieties of mimosa, it has several synonyms, in fact it is also called Acacia floribunda , Acacia semperflorens and mimosa of the four seasons. All these names make us understand that this plant has a long flowering period and in the warm areas of the south it has flowered almost all year round; although the flowering is continuous, it does not have the explosion of spring colour typical of Acacia dealbata . It forms a round crown 5/7 metres high and can also be proposed for city avenues, of course where the climate allows it. It is a beautiful plant with strange dark green leaves, narrow and elongated, 15/20 cm long.
Acacia retinoides reproduces from seed and can also survive in slightly calcareous soils.
Acacia retinoides ‘Imperialis’ : improvement of A. retinoides with canary yellow flowers larger than the species and more abundant flowering, even the phyllodes are larger and the bearing is more compact.With this variety it is possible to program the flowering with simple pruning, the period in which it is carried out allows floriculturists to program the period of the new flowering. In the Ligurian Riviera there are nurseries that use the characteristic of this variety to be able to sell flowering branches in every period of the year even in outdoor cultivations.
Acacia retinoides ‘Lisette’ : is an improved clone with larger flowers and more abundant flowering, very showy even in autumn.
A. x hanburyana ( A. dealbata x A. podalyriaefolia ): this curious variety with silvery grey phyllodes that resemble olive leaves was dedicated to Sir Thomas Hambury, creator of the Mortola gardens. Other compound leaves like the typical mimosa leaflets subsequently grow on this leaf. This botanical oddity can be explained by the fact that, as we have said, the entire leaves of the Acacias (phyllodes) are nothing more than enlarged petioles, so on this variety it simply happens that a real leaf grows on the petiole. It is a small tree or rather a large shrub that is not very resistant to the cold, which grows from 2 to 4 metres in height and has early flowering.
Acacia howittii ‘Clair de lune’ (Claire de lune): has drooping branches and thin, long, ash-grey phyllodes. It flowers late in March. It does not grow much and is perhaps the most graceful variety of mimosas in terms of its shape. Unfortunately, it is also one of the most delicate to the cold.
Acacia cultriformis (Cultriformis): small tree or large shrub that can grow up to 4 meters in height, has large and pointed phyllodes of a very light gray-green color, small non-scented flowers carried in erect clusters. It is a very decorative variety even when not in bloom.
Acacia podalyriaefolia (Motteana): has oval phyllodes similar to those of A. cultriformis but rounder, larger, soft and silky to the touch, glaucous in colour; it is a plant with limited growth, 4-5 metres at most, early, prolonged flowering and very fragrant flowers, with its flexible branches it is very well suited to being grown as an espalier against a south-facing wall.
In botany the only species that would have the right to be called mimosa is Mimosa pudica . The name comes from the Latin ‘Mimulus’ or ‘Mime’ an actor who can quickly change expression. It is a small thorny shrub with thin branches that in our climates is an annual plant. It has the curious characteristic that if even a small part of the leaf is touched, the whole leaf closes and immediately wilts as if it had suddenly withered, then within 15 – 30 minutes it returns to an upright position. In its natural habitat, which are the tropical areas of the Americas, it is a way to defend itself from the animals that graze on it, as soon as they start to eat it the whole plant wilts and takes on an unappetizing appearance for herbivores who thus move away.
The Acacias on the contrary are a very widespread family in almost all continents and include over a thousand species and varieties. The Acacia dealbata native to Australia has been improperly called mimosa and we do not know why, perhaps because of the great similarity that the flowers and leaves have with the Mimosa pudica but this name has finally taken root so much that today we tend to call almost all known species of Acacias mimosas while it should be kept only for the Acacia dealbata and its varieties. This term is also used as a female name and there are many women, certainly all beautiful like the mimosa, who can boast of this name.
The mimosa in the garden
Mimosa requires fertile, deep and above all fresh soil, better if slightly acidic. It does not tolerate drought and drought stress can even kill it. We prepare a hole as large as possible and bury a lot of mature manure. It is good to immediately provide a sturdy support because the seedlings, even if purchased small, grow quickly and in 3/4 years we can already have a large plant.
Watering is absolutely necessary in the first few years, it must be assiduous in the summer period and must continue even afterwards unless the soil is particularly cool. If we live in an area at the limit for temperature, we choose a more sheltered place that creates a microclimate and above all we plant varieties that are more resistant to the cold such as the dealbata from seed if the soil is not calcareous or the A. dealbata grafted or the A. dealbata ‘Rustica’.
The wind often shakes the large branches and sometimes even the entire plant. If there is this danger in the area, we choose a less exposed position or keep the volume of the crown reduced with pruning.
Fertilization. Essential in the first years, it is good to continue even later, with mature or pelleted manure and chemical fertilizer balanced in nitrogen/phosphorus and potassium, and it is better not to overdo it with nitrogen.
Pruning . They are useful because the branches grow too long and are subject to buckling. Pruning is done immediately after flowering and before the beginning of vegetation. The habit of picking flowering branches to decorate the house or give bouquets of flowers is not harmful, in fact it is a sort of pruning; at the end of flowering, with scissors, it is a good idea to give the plant a harmonious shape. If large branches are cut, it is a good idea to brush the cut with a fungicide product.
Notes on sowing by Marina Bardi
( Acacia dealbata 77,000 seeds per kg., Acacia saligna 27,000 seeds per kg.)
Acacia seeds, like all legumes, have very hard and waterproof teguments, which prevent the penetration of water and the beginning of the germination phase. To overcome this problem, they must be ‘scarified’. Scarification can be done mechanically by rubbing the seed with sandpaper or other abrasive or by immersing the seed in very hot water. Use as a proportion, three volumes of water and one of seeds; place the seeds in a bowl and pour over them the freshly boiled water. Do not increase the amount of water otherwise it will remain too hot for too long, damaging the embryo. Place the bowl in a warm environment and leave it there for 24 hours. If the seeds have not swollen, repeat the same treatment. Acacia sowing is done in spring or all year round in a warm greenhouse.