Acacia stenophylla (Shoestring Acacia)
Foliage: Evergreen
Mature Height: 20’ - 40’
Mature Width: 15’ - 20’
Growth Rate: Fast
Hardiness: 18 degrees F
Exposure: Full Sun
Leaf Color: Green
Shade: Filtered
Flower Color: Cream to Yellow
Flower Shape: Ball
Flower Season: Spring
Thorns: None
Propagation Method: Seed
Sizes Available: Not in production
Shoestring Acacia, Acacia stenophylla, combines two qualities that are rare among popular desert landscape trees: columnar (upright growth) structure and evergreen foliage. This Australian native was introduced to the desert southwest decades ago but gained wide popularity only in the last 10 to 15 years. Shoestring Acacia is reasonably fast growing maturing to a height of 20 to 40 feet with a 15 to 20 foot spread. The trees are moderately drought tolerant but cannot be naturalized to subsist on the annual rainfall in the desert southwest. Shoestring Acacia grows well in full sun or partial shade and is cold hardy to about 18 F. In Australia, where it is used as lumber and a food source for Aborigines, it is found growing at the edges of rivers and will tolerate periodic flooding and heavy clay soils. The tendency to grow along streams may explain two of its Australian common names, Native Willow and River Cooba (Cooba is the Australian common name for Acacia salicina). Best growth is achieved in well drained soil and regular deep irrigation.
Cream to yellow colored, ball-shaped flowers, in small clusters, (3 to 6 flowers/cluster) occur throughout the year with the majority produced in spring. Flowers mature rapidly to pods that resemble a string of pale green beads with pods constricted between each seed. Leaves (or phyllodes) are long and narrow approximately 1/4 to 1/2" wide and up to 12" long. Leaves are pale grayish green and are generally straight but can be slightly curved or twisted. Stenophylla's do produce some leaf, flower and pod litter.
The bark of maturing trees is rough, deeply textured and dark brown giving it a sharp contrast to the gray-green foliage. The columnar shape of the tree is the result of its weepy branches and leaves that hang down parallel to the upright main trunk(s). The narrow leaves are fairly dispersed giving the canopy a transparent, lacy quality that produces filtered shade. Its unique structure and open canopy allows Shoestring Acacias to be used in a variety of landscape applications. They are used in screen planting around the perimeter of properties or along streets or sidewalks. They are also used near or against taller structures to add color and graceful silhouettes to large walls. The filtered shade allows most flowering shrubs planted underneath Shoestrings to grow and flower normally. The columnar structure makes them ideal for planting in narrow or tight landscape settings. Trees can also be planted in small clusters or groupings without encountering tangled branches.
Trees may produce suckers if roots are exposed to the sun or disturbed. If not pruned these suckers will form clumps of trunks that may or may not be desirable. Small trees, 15 gallon and 24" box, are not striking and do not often reflect the ultimate shape and character of this specie. In desert landscape designs Shoestring Acacias are among the most versatile and well adapted trees for a wide assortment of landscape uses. They require limited pruning and to date have no reported serious insect or disease pests.
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 30% 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.
Acacia stenophylla is relatively free of serious insects pests.
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, thrip, 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 phytotoxicty. Always read label and follow label instruction before using pesticides. For pesticide control recommendations contact a licensed pest control advisor.
The information provided here was gathered from research literature published by the University of Arizona, other professional landscape and horticulture organizations and our experience at Arid Zone Trees. Always consult local landscape experts for recommendations for your specific area.