Scientific: Acacia stenophylla
Common: shoestring acacia
Family: Fabaceae (Leguminosae)
Origin: Broadly distributed across inland eastern Australia. Found mostly along river channels in Queensland, Australia in areas of 10 to 25 inches of rainfall per year.
Invasive alert: Shoestring acacia can reseed in the irrigated urban landscapes of Phoenix, but it is not locally invasive. However, 100 miles south of Phoenix in the pueblo city of Tucson (slightly higher elvation and cooler desert climate - Sunset zone 12), shoestring acacia shows a tendency to more aggressively reseed and is considered by many there to be an invasive tree.
Pronounciation: A-KAY-sha sten-o-FYE-la
Hardiness zones:
Sunset 8, 9, 12-24
USDA 9-11
Landscape Use: Silhouette tree, street tree, xeric landscape design themes, a great tree for narrow spaces if form is upright.
Form & Character: Strongly vertical and upright when young spreading with age, leaves and young stems and branches pendulous, weeping, open, airy, variable in shape from strongly upright to spreading, glaucous, semi-arid.
Growth Habit: Evergreen, woody, narrowleaf perennial tree, vigorous, upright when young to spreading with age, to 40-feet tall. Long, narrow young stems and branches often cross over other branches and grow back into the crown.
Foliage/Texture: Gray up to 16 inches long linear phyllodes (modified petioles that look like and function like leaves) contrast well with maroon colored twigs and young stems, trunk smooth when young changing to roughened dark gray to brown age; fine texture.
Flowers & Fruits: One-half inch small, cream-yellow puff-ball flowers originate from axillary meristems in November to January; fruit a long "chain" pod to 8 inches, constricted between seeds.
Seasonal Color: Flowers (only somewhat ornate) in late fall and winter.
Temperature: Very tolerant of lower desert heat, cold tolerant to 15oF.
Light: Full sun
Soil: Well-drained soils are best.
Watering: During summer heat, deep water established trees every two weeks, otherwise little to no water needed.
Pruning: Stake and train (prune) rigorously when young to establish a structurally sound scaffold branch system and to raise the crown. If left unpruned, then its canopy will trail to the ground and develop many weakly attached, acute branch angles with dangerous bark inclusions.
Propagation: From scarified (95% sulfuric acid best) seed, cuttings or
transplanted root suckers. Seedling plants are variable in shape in form.
Additional comments: Shoestring acacia (when properly trained) is truly an excellent upright tree for light shade and silhouette effects. It thrives under conditions of intense desert heat and drought and as such performs better than most trees in locations with copious impervious surfaces. Two significant concerns about this tree are that 1) it does need aggressive training when young to establish structural integrity and an aesthetic branch architecture and 2) it does shed a significant amount of leaf, flower and fruit litter. Shoestring acacia roots assist Rhizobium bacteria in fixing soil N2. It has a beautiful wood grain and grows heartwood that is of high quality, very hard and close-grained. The wood will take fine polish and is used for furniture and cabinetry.
Taxonomic note: The genus Acacia consists of an estimated over 900 species that are native to mostly Australia and the Pacific Islands, but also found in tropical Asia and Madagascar.
