Acacia smallii (Sweet Acacia)

Sweet Acacias are popular and well-adapted shade trees for arid region landscapes. Fragrant flowers, upright stature and rapid growth rate makes it desirable for commercial and residential landscapes. It is used as a theme tree in streetscape planting or at development entries but is probably used most often as individual accent trees in mixed desert planting. Most of the literature reports that trees mature to a height of 15’ to 30’. Our experience has been that trees may reach 35’ to 45’ and may be 30’ wide.

Mature trees are best adapted to full sun, well draining soils and infrequent deep irrigation. They tolerate both desert and lawn plantings. Standard and multiple trunked specimens are equally popular. Rapid tree growth coupled with the tendency of this tree to produce new branches all along the trunk make regular, moderate pruning a maintenance must.

Leaves are made up of 10 to 20 pairs of tiny oval leaflets giving the leaf canopy a delicate, fern-like appearance. Unpruned mature trees provide fairly dense shade and inhibit the growth of flowering understory plantings. Sweet acacias are semi-deciduous. In warmer winters or in certain microclimates trees may retain a majority of the leaf canopy. Leaves are shed in spring with the resumption of new growth.

Bloom period seems to be somewhat variable depending on the severity of winter cold temperatures. In years with mild fall weather flower buds may appear on some trees in November and December with blooms persisting into late winter and early spring. Other specimens may not begin blooming until mid to late spring with flowers lasting until April to late May. Mature seed pods are dark brown, cylindrical, 2 to 2 1/2 long and 1/4 to 3/8" in diameter.

TAXONOMY Plant taxonomy is the science of organizing plants into established categories and giving them names (a Latin binomial), based on their characteristics. Originally this tree was called Acacia farnesiana after the 17th century Roman Cardinal Odoardo Farnese. Since the late 1960’s plant taxonomists have been troubled by the wide variety of horticultural characteristics (flowering periods, cold hardiness etc.) exhibited by Sweet Acacias. In 1969 it was proposed that Sweet Acacias actually represented two different tree species. Acacia smallii was proposed as the name for all the Sweet Acacias occurring from California to western most Florida and Acacia farnesiana for those trees found in the balance of Florida and the Caribbean.

The horticultural characteristic of greatest interest to landscape professionals in the desert southwest is cold hardiness. Experience over the last 10 to 15 years has shown that Acacia farnesiana is severely (sometime fatally) damaged by temperatures below 20 degrees F. In contrast Acacia smallii appears hardy to about 10 to 20 degrees F. and survives most central and southern Arizona and southern California winters injury free. While there are other physical (tree structure) and botanical distinctions between these two species the greater cold hardiness of Acacia smallii is of most interest to landscape professionals. Arid Zone Trees distributes Sweet Acacias in Arizona, Nevada and California. The various communities within these states experience different low temperature extremes in any given winter. As a result we only grow Acacia smallii, and we constantly are looking for selections to propagate that have exhibited the highest levels of cold hardiness that we can identify