Sweet Acacia (Acacia smallii) takes its common name from the unmistakable fragrance of its bright yellow ball flowers. It brings color, shade and a desert character to any landscape setting. Fragrant flowers, upright stature and rapid growth rate makes it desirable for commercial and residential landscapes. Popular as a theme tree in streetscape planting or at development entries it is probably used most often as individual accent trees in mixed desert planting or in small groupings.

Sweet Acacias like other desert natives have slender, white to gray thorns along the branches. These thorns are conspicuous, readily visible and pose little risk to pedestrians. They are frequently used in street and sidewalk plantings as well as in parking lots. Their abundant shade and moderate stature contributes to their use in courtyards, patios, seating areas and near building entries. If desired, thorns on lower branches are easily removed with hand pruners.

Mature trees are adapted to full sun, well draining soils and infrequent deep irrigation. They will thrive in both desert and lawn plantings. Much of the literature reports that trees mature to a height of 15' to 30' but some mature specimens in the Phoenix-metro area have reached 35' to 45' and may be 30' wide. Single and multiple trunked specimens are equally popular. Like most desert adapted species, multiple trunked and low branching specimens best capture the natural character of the tree and improves resistance to wind damage. These spreading, mature specimens maximize the flower display and the accompanying fragrance.

Leaves are made up of 10 to 20 pairs of tiny, dark green, oval leaflets giving the leaf canopy adelicate, fern-like appearance. Unpruned mature trees provide dense shade and can inhibit the growth of flowering under-story plants and turf. Sweet Acacias are semi-deciduous. In warmer winters or in certain protected microclimates trees may retain a majority of the leaf canopy. Remaining leaves are shed in spring with the resumption of growth and the development of new leaves.

Bloom periods are somewhat variable depending on the severity of winter temperatures and the inherent genetic variability found in this specie. In years with mild fall weather flower buds may appear December through February with blooms persisting into late winter and early spring. Other specimens may not begin blooming until mid to late spring and continue flowering into April and late May. Mature seed pods are dark brown, cylindrical, 2 to 2 1/2 long and 1/4 to 3/8" in diameter.

Plant taxonomy is the science of organizing plants into grouping or categories and giving them names (a Latin binomial), based on agreed upon physical characteristics. Originally Sweet Acacia was named Acacia farnesiana after the 17th century Roman Cardinal Odoardo Farnese. Sweet Acacias have been found in tropical and semi tropical climates all over the world, including North America, South America and Africa. Since the late 1960's plant taxonomists have been troubled by the wide variety of horticultural characteristics (flowering periods, cold hardiness etc.) exhibited by the large and dispersed population of trees identified as Acacia farnesiana. Over the last 20 years several attempts have to made to address this variability leading to Sweet Acacia being identified as A. smallii, A. farnesiana and A. minute. 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 20-25 degrees F. In contrast, Acacia smallii appears hardy to about 15 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 the main reason it has become the more popular of the two Acacia species*.

Pruning and shaping Sweet Acacias, especially during the first few years, is essential for establishing the form and structure of the mature tree. Because of their many desirable qualities (flowers, shade, dark green canopy) these trees are used in a wide array of landscape settings. When designing this tree into the landscape appreciate that mature specimens will generally be as wide as they are tall and, with optimal growing conditions, can grow to 30 feet. Rapid tree growth coupled with the tendency to produce new branches all along the trunk make regular, moderate pruning a maintenance must. This succulent growth is ideally removed in the ½" to 3/4" diameter stage when it is easily cut with hand pruners or loppers.

Sweet Acacias possesses the best qualities of two other popular desert trees, Blue Palo Verde and Thornless Mesquites. It brings a brilliant floral display to the landscape, like those of Blue Palo Verde, in combination with a lush, deep green canopy, like Thornless Mesquite. With these qualities it is not surprising that it is among the most widely used desert trees.

*NOTE: Arid Zone Trees (AZT) distributes Sweet Acacias in Arizona, Nevada and California. The various desert communities within these states experience different low temperature extremes in any given winter. As a result, AZT only grows Acacia smallii. We are continuously looking for selections to propagate that exhibit the highest levels of cold hardiness that we can identify.