Acacia rigidula (Blackbrush Acacia)
Foliage: Deciduous
Mature Height: 10’ - 15’
Mature Width: 10’ - 15’
Growth Rate: Moderate
Hardiness: 15 degrees F
Exposure: Full Sun
Leaf Color: Green
Shade: Filtered
Flower Color: Yellow to Cream
Flower Shape: Rod Shape
Flower Season: Spring
Thorns: Yes
Propagation Method: Seed
Sizes Available: not in production at AZT
Acacia rigidula (Black Bush Acacia) is native to western and southern Texas and a several northeastern Mexican states. In natural setting it is typically found on rocky hillsides and along canyon floors at elevations from 1100 to 1800 feet above sea level. It occurs as scattered individual plant and in clumps or thickets. Under natural growing conditions the tree matures to about 10 to 15 feet tall and as wide but will likely grow larger in landscape settings. Arizona boasts the co-national champion Black Bush at 26 feet tall, 29 feet wide and a trunk diameter of 16 inches as designated by the Arizona Chapter of the National Registry of Big Trees.
Yellow to cream colored flowers arranged in 2 to 3 inch long, slender spikes appear from March to mid-June. Slender pods about 3 inches long develop from these flowers. The tree is deciduous and the branches are armed with numerous thorns. Black Bush thrives in full sun and a variety of soil types and conditions including very poor calcareous (caliche) soils. Trees grow at a moderate to slow rate. Regular irrigation is needed for establishment but, in the absence of severe drought, can be naturalized to survive on desert rainfall. Monthly summer irrigation of mature, established trees optimizes growth and appearance. Immature trees are sparse and rangy, becoming increasingly dense as they reach maturity.
Part of the unique charm of this tree, besides its modest statue, is its dark green, glossy, closely spaced foliage, borne on stiff, densely packed, gray barked branches. In summer Black Bush is easily mistaken for Texas Ebony (Pithecellobium flexicaule). These qualities combine to make Black Bush an excellent screen, barrier or foundation plant, as a backdrop for other flowering plants in the landscape or for erosion control. Specimens can be left as a large mounding shrub or pruned to a sculptural tree form that accents the contrast between green leaves and gray bark. As a deciduous tree it is best used in combination with evergreen trees or shrubs.
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.