Our very mild late winter and spring has suited tender plants, such as Mimosa, Acacia dealbata. There are several Mimosa trees in Norwich and they have been flowering for weeks now, lighting up front gardens with the bright yellow puffs of their flowers. As I write, some of the flowers are beginning to turn brown with age, but from a distance the effect is still magnificent. Close up, the flowers have a delicious scent. The Fragantica website describes this as a “child-like, sweet, soft and hazy heliotrope-smelling note with sugar-spun tonalities”. Mary Keen describes the scent as the “smell of southern spring“.  They smell nice, anyway.

Acacia dealbata is a native of southeastern Australia (New South Wales, Victoria, Tasmania and the Australian Capital Territory). It was introduced into Southern France in 1820 and is now widely planted and naturalised in many parts of the world with a suitable climate, including other parts of Australia, the Mediterranean region from Portugal to Greece and Morocco to Israel, the Black Sea coast of Russia, Ukraine, California, Madagascar, South Africa, Zimbabwe, the highlands of southern India, south-western China and Chile. It can be a serious weed in New Zealand and parts of South Africa.

Mimosa is a member of the Fabaceae, the Pea family. Other English names include Silver Wattle and Blue Wattle. In its native land Acacia dealbata is a pioneer species that colonises after a bush fire. The roots have nitrogen-fixing bacteria in their nodules, and can bind together soils to prevent erosion. Mimosa grows rapidly to about 30 metres (100 feet) tall but seldom lives longer than thirty to forty years. In the UK, it is more likely to reach 8 – 12 metres (26 – 40 feet) tall and frost, rather than natural causes or fire, is likely to end its life.

In the UK, growing Mimosa is often a bit of a gamble and “probably not something to try out of doors north of the Trent“. It can survive brief cold spells down to -10°C, but it is officially given a hardiness rating of H3 by the RHS: Hardy in coastal and relatively mild parts of the UK (-5 to 1°C).  It would probably not survive a cold winter like 2009 and 2010, though most winters are now milder in the south of England.

Shrubs such as Leptospermum are equally tender but small enough to cover in the winter, whereas Mimosa can become too tall to wrap up against the chill. It is most likely to survive in a sunny, sheltered spot in well-drained soil. If cut down by frost, it may regrow as a multi-stemmed shrub. If you need to prune your Mimosa, follow the RHS instructions for Early flowering evergreen shrubs (pruning group 8) – prune after flowering.

Acacia dealbata subspecies ‘Subalpina’, which grows at higher altitudes, is a bit hardier than the wild type and said to be worth seeking out: at the time of writing it is stocked by Shoot. James Wong mentions a related dwarf form, Acacia nanodealbata (sometimes spelt nono-dealbata). Anna McKane describes some other hardy (ish) Acacia species in her 1996 article in The Independent, “On the trail of hardy mimosas“.

Mimosa trees can be raised from semi-hardwood cuttings or from seed, though the seeds need to be treated with boiling water and then left to soak for a day. The boiling water mimics the heat of a fire that would trigger germination in the wild.

The Plants for a Future website tells us that Mimosa gum (which exudes from the trunk) is edible, and can be used as a substitute for gum arabic. The real thing comes from two close relatives: Senegalia senegal (Gum Acacia) and Vachellia seyal (Red Acacia).

Mimosa flowers are often sold by florists. The flowers are edible when cooked and according to Plants for a Future can be made into fritters, although the recipes I found when searching for “Acacia flower fritters” used the white flowers of the related Black Locust tree,  Robinia pseudoacacia.  Mimosa can be used as a dye plant, either for yellow (the flowers) or green (the seed pods).

Mimosa Salad sounds appetising, but no Mimosa was harmed (or used) in making it. A festive salad in the former USSR, its main ingredients are cheese, eggs, canned fish, onion, and mayonnaise. If boiled egg yolk is crumbled and scattered on its surface, it is said to resemble mimosa flowers scattered on snow.

Mimosa against a blue March sky.