Focus on the difference between mimosa and acacia
Confusion can arise from the Latin name of the different species of mimosa, such as Acacia dealbata, Acacia baileyana, Acacia decurrensetc.. It is therefore important to know that mimosa is a plant belonging to the genus Acacia and that all plants bearing the name of this genus in their Latin name are mimosas.
They should therefore not be confused with the shrubs that we commonly and wrongly call “acacia”, which, for their part, belong to the Robinia genus and are black locust trees, such as Robinia pseudoacacia, or false-acacia black locust. The plants we are going to talk about here are therefore mimosas of the Acacia genus, that is to say trees or shrubs, depending on the variety, which can be grown in the ground or in pots.
History of Mimosa in France
Originally from Australia, the mimosa was brought to France at the beginning of the 19th century by the explorer Nicolas Baudin. The feet thus brought back were planted in the gardens of the Château de Malmaison, home of Empress Joséphine de Beauharnais. These trees seduced perfumers who saw in them a golden windfall and, around the 1880s, the mimosa was massively planted on the Côte d’Azur where the climate was favorable to it.
It has naturalized so well in this region that it is now considered an invasive plant. Thus, it is now classified as an “invasive exotic species”. Because it cannot withstand extreme cold, it is found throughout the Mediterranean, but also on the Atlantic coast. It is therefore very present in the south-west of the country and as far as the edge of the English Channel.
Why is mimosa considered an invasive plant?
Mimosa is also considered invasive in other countries in Europe and the world, such as Spain, Italy, Portugal, etc. In France, in regions other than the south of France, such as regions Midi-Pyrénées and South Atlantic, it is considered to be monitored and in the Pays de la Loire region, it has been classified as a “Potentially invasive plant”.
The reasons for these classifications as a proven invasive plant and a potentially invasive plant in regions where mimosas have become naturalized thanks to growing conditions that are perfectly suited to them are twofold:
- The production of numerous suckers : Indeed, the capacity of mimosas to produce suckers is impressive and is observed even after events such as frost episodes or fires. Suckers are suckers that start from the roots and can go far enough to give rise to new trees. This means that if the tree is destroyed or uprooted, its underground roots continue to live and produce suckers.
- The mode of reproduction of the mimosa : The mimosa can reproduce sexually via the numerous seeds that are produced, but also vegetatively via the numerous suckers. These modes of reproduction therefore favor its excessive spread and its problematic concentration in certain areas.
The consequences of this massive spread
The consequences are of two types:
- Biodiversity imbalance : It is easy to understand that faced with this ability of the mimosa to reproduce quickly and easily, the regions of the south of France and more particularly the PACA region find themselves with areas where other local and indigenous species can no longer develop. . This poses significant management problems, because this proliferation of mimosa in the natural environment cannot be controlled and directly threatens the biodiversity of these areas. Indeed, we must be aware that the concentration of a single species is damaging to ecosystems.
- Impact on soils : Let us add to this that mimosas have an impact on water flow and soil erosion. This is due to two facts: the first is that their too high concentration creates impermeable zones and the second is that the mimosa is part of the Fabaceae family, a family of plants which fixes nitrogen in the soil. This is good in itself, but like everything else, too much creates an imbalance: in this case, the increase in nitrogen levels is much too great in these areas.
Ways to fight
Faced with these numerous problems, control methods have been put in place in the regions: young plants are uprooted, large plants are cut, stumps and suckers are uprooted and seeds that have fallen to the ground are removed. From now on, to avoid rejections when a mimosa is cut, the stumps are systematically treated either mechanically or chemically.
Does this apply to a mimosa to plant in your garden?
The picture drawn is rather bleak, but it concerns natural areas. If you want to plant a mimosa in your garden, you can do so without worrying too much, because solutions exist:
- Concerning the production of rejects: Acacia dealbata is a mimosa characterized by significant suckering, so it is one that you should avoid at all costs. The solution lies in grafted subjects which are now offered for sale, such as Acacia retinodes which has little suckering, but is less hardy.
- Concerning the allergenic nature : It is common to hear that Mimosa can be bothersome for people sensitive to pollen or hay fever. However, the impact of mimosas on seasonal allergies is limited since it is an entomophilous plant, which means that its pollen is dispersed by insects and not by the wind, like that of anemophilous plants which are the most allergenic. . Furthermore, since pollen grains are heavier, they fall to the ground more quickly.
- Concerning the roots : Acacia dealbata has a powerful root system which can cause damage to foundations or pipes, or lift floor coverings. This problem can be avoided by opting for a subject grafted on Acacia retinodes, which is also called mimosa of the 4 seasons.
- Regarding the allelopathy problem : It is a biological phenomenon that appears when a plant, such as mimosa among many others, produces substances that have an impact on the germination, development and reproduction of other plants. Thus, at the time of flowering, the leaves and flowers of a mimosa will release a substance of this type. It can therefore be difficult to grow plants under its branches. The good news is that, a priori, periwinkles, euphorbias or grasses are not sensitive to these substances.