Mimosa acacias are not mimosa trees at all. People call silver wattle (Acacia dealbata) and Bailey acacia (Acacia baileyana) mimosa acacias because they have foliage and puffy flowers that resemble those of Albizia julibrissin--the mimosa, or silk tree. Many nurseries stock silver wattle and bailey acacia. Both trees thrive in moderate-winter areas that receive a modest amount of rainfall.
Silver wattle trees are native to southeastern Australia and Tasmania, where they grow wild along streams and in forested areas. Yearly rains average between 20 and 40 inches. Bailey acacia also comes from southeastern Australia and tolerates drought well. The trees thrive in coastal areas and in drier and hotter inland areas.
Acacia flowers produce pollen that honeybees collect. The resulting honey is pale and clear, and it is the only honey that does not crystallize over time. Birds eat seeds that form on acacias, and the dusky-footed woodrat uses its dried and fallen branches to create elaborate twig homes under the shelter of the tree's canopy.
Growth Habits and Needs
Both varieties of acacia grow quickly. Too much supplemental water causes excess rank growth, weak branching structure and early death. Bailey acacia is more drought tolerant than silver wattle, but both tolerate dry conditions well. Provide good drainage and neutral PH soils. Acacias do well on rocky or arid slopes. Frost can damage some foliage, but mature trees survive. Young tender seedlings might not survive temperatures below 20 degrees F.
Flowers and Foliage
Mimosa acacias have fine, ferny and soft foliage. Acacia baileyana has blue-gray leaves and Acacia dealbata has silver foliage and branches. Profuse golden or bright-yellow fluffy flowers cover the tree canopy in spring. Many people prize the flowers for bouquets, and the foliage is also useful, providing color and volume to arrangements.
Landscapers rely on tough acacias for parks, parking lots and roadsides. Silver wattle and bailey acacia endure pollution and tolerate poor soils. Acacias work in residential settings if given enough room to spread. The trees reach up to 40 feet high and 40 feet wide. Australian acacias, such as the mimosa varieties, do not have spiny branches. The flowers do attract bees, though, and the roots can lift patio paving. Both varieties make good hedges and tolerate shearing well.
Silver wattle and bailey acacia need good air circulation and limited supplemental irrigation. Growing the trees in irrigated lawns might shorten their lifespan. Acacia flowers produce a lot of pollen, and some people experience allergies when the tree is blooming. Mimosa acacias naturalize in areas that have similar climates to southeastern Australia. Naturalists in these areas consider the trees invasive because they spread rapidly in wilderness buffer zones. The acacias have shallow roots, and hillside trees tend to topple over after heavy rains--the lush, broad canopy overwhelms the root system. After a few years of growth, the trees build up dead twigs and wood. Clear out accumulated dead material from acacias to prevent fire hazards.