Acacia smallii ‘AZT™’ (AZT™ Sweet Acacia)
Acacia smallii ‘AZT™’ (AZT™ Sweet Acacia) is one of the recent additions to our expanding inventory of cloned desert trees. It 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, and wonderfully fragrant flowers, it’s not surprising that it is among the most widely used desert trees. Showy, 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.
Originally Sweet Acacia was named Acacia farnesiana after the 17th century Roman Cardinal Odoardo Farnese. Sweet Acacias can be 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 geographically dispersed population of trees identified as Acacia farnesiana. Over the last 20 years several attempts have been made to address this variability leading to Sweet Acacia being identified as up to four differently species; A. smallii, A. farnesiana and A. minute; then most current Vachellia farnesiana.
The horticultural characteristic of greatest interest to landscape professionals in the desert southwest is cold hardiness. Experience over the last 15 to 20 years had shown that Acacia farnesiana is severely (sometime fatally) damaged by temperatures below 20-25 F°. In contrast, Acacia smallii appeared hardy to about 15 to 20 F° and survived 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 Sweet Acacia species. The need for consistent, predictable cold hardiness make Sweet Acacia an ideal candidate for clonal propagation and AZT began the search for Mother trees that possessed sound branch and rooting structure, flowering characteristics and possessed reliable cold hardiness to at least 20 degrees F°.
Seed grown Sweet Acacia have exhibited high variability in some critical horticultural characteristics. Some common variations, like canopy and leaf density, bark texture, and flowering have little impact on tree longevity or durability. Wide and significant differences in cold hardiness, from tree to tree, have lead to catastrophic, wide spread damage to some trees during severe desert freezes. Like all Variety Acacia smallii ‘AZT™’ (AZT™ Sweet Acacia) is propagated from cuttings (cloned) and is the product of an extensive screening process that begins with horticultural qualities, like cold hardiness, rooting characteristics and overall durability. Once these qualities are identified, we look for potential Mother trees whose physical appearance reflects the natural beauty that have made Sweet Acacia a landscape staple in desert landscapes. Acacia smallii ‘AZT™’ (AZT™ Sweet Acacia) consistently exhibits cold hardiness down to 15-20 degrees F°.
The literature describes mature Sweet Acacias at a height of 15’ to 30’. Our experience with Acacia smallii ‘AZT™’ (AZT™ Sweet Acacia) has been that trees may reach 35’ to 45’ and may be 30’ wide. Mature specimens are best adapted to full sun, well draining soils and occasional deep irrigation(s). They tolerate both desert and lawn plantings. Rapid tree growth coupled with the tendency to produce new branches all along the trunk make regular, moderate pruning essential to good maintenance. Leaves are made up of 10 to 20 pairs of tiny oval leaflets giving the leaf canopy a delicate, fern-like appearance. Un-pruned mature trees provide dense shade that may inhibit the growth of flowering understory plantings. Acacia smallii ‘AZT™’, AZT™ Sweet Acacia is 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 growth.
Acacia smallii ‘AZT™’ (AZT™ Sweet Acacia) is one of the first desert trees to bloom in the spring. Flowers of AZT™ Sweet Acacia appear in February, March and continue to be produced until approximately April. Mature seed pods are dark brown, cylindrical, 2 to 2 1/2 long and 1/4 to 3/8" in diameter. The bloom period for seed grown selections seems to be somewhat variable depending on the severity of winter cold temperatures and the selection planted. 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.
Cultural Practices:
Foster the development of a more dispersed root system and reduce the risk of wind throw by arranging irrigation emitters at varying distances from the trunk to encourage roots to "seek out" water and nutrients. Irrigation emitter arrangement along with other information on irrigations practices for desert trees can be found at Irrigation Practices for Desert Trees.
Prune as needed to reinforce the structure and form of the tree. Periodic thinning is the most desirable method of pruning. Avoid hedging or heading back desert species, as this will only stimulate excessive branching. Do not remove more than 20% of the canopy during the summer as this can lead to sunburn injuries that can later be invaded by wood boring insects. Always use clean, sharp tools that are cleaned regularly in a 10% solution of bleach. For detail pruning guide see Pruning Desert Trees.
Periodically insect pests can be a problem on some desert trees. On young trees, insect infestation can slow typical seasonal growth. Inspect trees during the growing season for common garden sucking insects such as aphids, thrips, whiteflies or psyllids. During dry months, (May and June) in dusty conditions, spider mites can appear. Monitor for infestation and apply controls as needed. Spray applications of water or water and Safer Soap give short-term control (3 to 7 days) for small insect population. For heavy infestation or longer control use federally registered insecticides. A contact insecticide application will kill existing adults. An application with a systemic soil drench will provide 8 to 12 weeks control for any post application insect hatchings or migration of insects. Before using pesticide for the first time or on new plants or cultivar, treat a few plants and check for phytotoxicity. Always read label and follow label instruction before using pesticides. For pesticide control recommendations contact a licensed pest control advisor.