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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. |
