Tree
Willow Acacia
Acacia salicina · Fabaceae
Also called: Australian Willow, Weeping Acacia, Cooba
Willow Acacia (Acacia salicina) is a low-water tree well suited to Tucson and the low desert. It grows to 25-40 ft H x 15-20 ft W in full sun, with a fast growth rate. Expect creamy white to pale yellow blooms Sporadically year-round, with peak bloom in late winter to spring.
Willow Acacia at a glance
- Water use
- Low (established)
- Sun
- Full sun
- Mature size
- 25-40 ft H x 15-20 ft W
- Growth rate
- Fast
- Bloom
- Creamy white to pale yellow, Sporadically year-round, with peak bloom in late winter to spring (and again in fall)
- Cold hardiness
- Hardy to about 15-18 F; USDA zones 9-11
- Soil
- Tolerates a wide range of well-drained soils including caliche; prefers good drainage and is sensitive to standing water.
- Native range
- Australia
- Best used as
- Shade tree, Screen, Windbreak, Streetscape/median tree
- Wildlife
- Flowers attract bees and other pollinators; provides cover and nesting sites for birds.
- Toxicity
- Not considered significantly toxic; foliage and pods are generally regarded as low risk, though Acacia seeds are not for human consumption.
How to grow Willow Acacia in Tucson & the low desert
Watering
Deep, infrequent irrigation; water established trees deeply about every 2-3 weeks in summer to a depth of 3 ft. Avoid frequent shallow watering, which promotes weak, shallow roots and increases blow-over risk.
Fertilizer & nutrients
Generally not needed; as a nitrogen-fixing legume it requires little to no fertilizer. A single light application of balanced fertilizer in spring can help young trees establish.
Pruning & care
Prune in late spring/summer to develop strong scaffold branches and a single dominant leader; thin the dense canopy to reduce wind resistance and prevent toppling. Avoid heavy topping.
Notes
Fast-growing weeping-form tree valued for quick shade, but the rapid, brittle growth and dense canopy make it prone to wind damage and limb breakage; it is also relatively short-lived (often 15-30 years). Can sucker and reseed. Has shallow, aggressive surface roots near excess water. Drops fine litter from phyllodes and pods.
Sources: AMWUA 'Landscape Plants for the Arizona Desert'; University of Arizona Cooperative Extension; Arizona-Sonora Desert Museum; Arid Zone Trees grower references