Tree · Sonoran native
Sweet Acacia
Vachellia farnesiana · Fabaceae
Also called: Sweet Acacia, Huisache, Needle Bush, Perfume Acacia, Acacia farnesiana (syn.)
Sweet Acacia (Vachellia farnesiana) is a low-water tree native to the Sonoran Desert region well suited to Tucson and the low desert. It grows to 15-25 ft H x 15-25 ft W in full sun, with a moderate to fast growth rate.
Sweet Acacia at a glance
- Water use
- Low (established)
- Sun
- Full sun
- Mature size
- 15-25 ft H x 15-25 ft W
- Growth rate
- Moderate to fast
- Bloom
- Golden yellow (fragrant, round puffball flower heads), Late winter through spring (Feb-April), sometimes with sporadic later bloom
- Cold hardiness
- Hardy to about 15-18 F; USDA zones 9-11. May show frost tip damage in cold Tucson winters but recovers; semi-evergreen to briefly deciduous.
- Soil
- Well-drained soils; tolerates poor, rocky, sandy, and alkaline desert soils. Needs good drainage.
- Native range
- Native to the southwestern U.S. including southern Arizona (e.g., Pima/Santa Cruz counties) and widely through the American tropics/subtropics and Mexico; pantropical in distribution. Native to the Sonoran Desert region, though uncommon in the wild in Arizona.
- Best used as
- Fragrant flowering accent and small shade tree, Patio, courtyard, and streetscape tree (site away from high-traffic areas due to thorns), Wildlife/pollinator and native habitat plantings
- Wildlife
- Highly fragrant flowers are an important early-season nectar/pollen source for bees and butterflies; host plant value for native insects; pods/seeds eaten by birds and mammals; thorny canopy provides protected bird nesting and cover.
- Toxicity
- Not significantly toxic to humans; flowers have been used in perfumery (source of 'cassie' essential oil). Sharp paired thorns are the main hazard. Foliage is browsed by livestock and generally not considered poisonous.
How to grow Sweet Acacia in Tucson & the low desert
Watering
Drought tolerant once established; deep irrigation every 2-4 weeks in summer keeps it attractive, with little water needed in cooler months. Tolerates more water but supplemental deep watering during establishment is important.
Fertilizer & nutrients
Generally not needed; nitrogen-fixing legume thrives in lean soils. A light spring feeding can support young trees if desired, but mature trees rarely require it.
Pruning & care
Train to single or multi-trunk form when young; prune in late spring/summer to lift and shape the canopy and remove low, twiggy, or crossing branches. Be cautious of the sharp paired thorns. Avoid heavy pruning that stimulates weak watersprouts.
Notes
Formerly Acacia farnesiana; Vachellia farnesiana is the currently accepted name after the Acacia genus split. Valued for intensely fragrant golden late-winter/early-spring flowers that signal the end of winter in Tucson. Armed with sharp thorns, so place thoughtfully. Litter from flowers and pods occurs. Drought- and heat-tough; one of the showier small native desert legume trees.
Sources: Arizona-Sonora Desert Museum; AMWUA "Landscape Plants for the Arizona Desert"; University of Arizona Cooperative Extension; SouthwestDesertFlora.com; Lady Bird Johnson Wildflower Center