by Leza Bennetts and Erika Birmingham
Acacias are evergreen, nitrogen-fixing plants ranging in form from ground covers to tall trees. There are more than 1200 species worldwide.
There are many roles for acacias in permaculture design such as increasing soil fertility through nitrogen fixation, rehabilitation of degraded soils and in reforestation. They are useful for erosion control due to their rapid growth and effective seed dispersal, and many species sucker readily.
Most species are extremely hardy and drought tolerant and some are salt tolerant, making acacias particularly valuable in arid regions as timber, firewood, food and fodder for stock during drought.
Few acacias live in rainforests, as most cannot tolerate humid conditions, wet or clay soils, hence most are found in more arid climates.
Several acacia species produce high quality timber for cabinet-making and craftwork. Others provide a useful hardwood for fencing, building and firewood.
Until recently, many species of acacia were considered poisonous to domestic animals, however recent research has shown that suitable varieties can be grown as fodder crops for use as a supplement in drought conditions.
Seeds from acacias were once a staple food for Aboriginal people in Australia, as they were readily available, could be dried and stored for long periods of time and were easy to carry. Aborigines also used acacias medicinally and for fibre. The seeds have been analysed by nutritionists and have proved to contain higher levels of protein than wheat or other similar crops. Two species, A. tennuissima and A. coriacea, have the most palatable seeds.
Acacias are also an important source of pollen for attracting bees and birds, which are essential in orchards for pollination and pest control. Two useful species which flower almost all year round, are A. deanei (Deane’s Wattle) and A. retinoides (Wirilda).
Size is an important criteria for species to be planted in orchards. If too large they will compete for light and nutrients and can cause extensive damage to fruit trees when removed. Larger acacias may be more beneficial planted as a windbreak around orchards and replaced within orchards by a nitrogen-fixing ground cover.
Care in selection is important, for example, species must be borer resistant in, or near, orchards. A. decurrens is a host plant for the fruit tree borer which damages stone fruit. Acacias also have the potential to become a noxious weed, especially the suckering varieties. Wherever possible, planting of local species is preferable.
Click here to see a chart listing some acacia species chosen for their multiple uses in permaculture design.