Acacia dealbata

Acacia dealbata

Seeing the picture of acacias on the Algarve on the cover of the May 2009 Pentachondra prompted me to write this article about Acacia dealbata.

A. dealbata is confined to Tasmania, Victoria, New South Wales and the Australian Capital Territory where it has the common name of Silver Wattle. In the United Kingdom it is called Mimosa or Florists’ Mimosa and  it used to be sold in posies or bunches by florists and even from street barrows in London. Flowering branches came into England from southern France but it is many years since I saw Mimosa on sale. Whilst much admired as a cut flower in Europe, in Australia it is considered bad luck to bring cut branches in flower into the house.

In southern parts of Australia it can make a shrub but more often it is a tree, especially in Tasmania where it can reach or even exceed 100 feet (30 metres). Most species of Australian acacia have their leaves replaced by phyllodes which are hard and spiny (see Jeff Irons’ article on the botany of Acacia in Pentachondra December 2008, page 8). Acacia dealbata has true bi-pinnate leaves which are silvery-grey, hence the common name. New stems and young leaves have a silvery pubescence which intensifies the leaf colouring. There are forms in which the leaves are glaucous rather than silvery, becoming almost blue in some selections. It was the blue leaved forms that were favoured by florists. In my experience, these forms are less hardy than the silvery grey ones.

Flowering occurs in winter or early spring. The yellow spheroidal heads of tiny fragrant flowers form large panicles. In the open this species tends to be tender and has not been reliably hardy in Britain except perhaps for the south west. But after 20 years of mild winters it might well be that it has become more widely established and plants have grown to flowering during that period. Flowering is variable and is dependent on summer warmth in the year before flowering.

My experience of it in southern England was in the earlier decade of the 1980s when cold winters with snow were frequent. I raised saplings from a range of wild collected seed from many sources. These were planted at the foot of a high south facing wall with most being killed off during the first winter. If they survived this stems were thicker and  roots had penetrated deeper and as a result these saplings were more likely to survive the next winter. My best result was with saplings raised from high altitude Tasmanian seed. One of these survived for four winters and  reached  a height of 15 feet (nearly 5 metres) only to be killed in the next.

Wattles are easy to raise from seed. Pour boiling water over the seed and allow it to remain in the cooled water for 24 hours before sowing. In my experience A. dealbata requires an acid soil and yet one can read in books that it will tolerate some alkalinity. Most usually, even in the milder winters, shrubs/trees will be grown against a south facing wall and this needs to be of considerable height.

A memorable experience, from when I was flying over Tasmania in winter on a journey from Melbourne to Hobart, was to see through the portholes mountain tops which were golden with the flowers of Silver Wattle.

Author: Brian Halliwell

Published: Issue 43 (December 2009)