A small, fast-growing tree, knife acacia, also known as knifeleaf acacia (Acacia cultriformis) displays droopy branches densely covered with small, silvery leaves shaped like knife blades. Clusters of sweet-scented, yellow flowers, which appear in spring, are often used in floral arrangements. At maturity, knife acacia reaches a mature height and width of 10 to 15 feet. After it is established, this drought-tolerant tree requires little care, making it a good planting choice for busy moms. Knife acacia grows in U.S. Department of Agriculture plant hardiness zones 9 through 10.
Water knife acacia once every three to four weeks during summer when moisture isn't provided by rainfall. Water deeply, using a garden hose to saturate the soil to a depth of 2 feet; infrequent, deep watering results in long, sturdy roots and a healthier tree. Let the soil dry before watering again, as acacia is adapted to dry climates and tolerates long periods of drought.
Maintain 2 to 4 inches of mulch around the tree. Use an organic mulch such as compost, bark chips or pine needles, which keeps the soil moist and keeps weeds in check. Additionally, organic mulch provides nutrients to the soil as it decomposes. When properly mulched, knife acacia requires no supplemental fertilizer.
Allow an unmulched span of at least 6 inches around the trunk, as mulch may attract rodents and other pests that chew on the trunk. One way to protect the trunk from rodents is to place a 6-inch circle of gravel, pebbles or crushed stone around the trunk.
Prune acacia in autumn or early spring. Although acacia generally requires little pruning, the tree benefits from thinning to make it more wind resistant. Trim dead and damaged branches and remove unsightly growth or branches that cross or rub against other branches. If you want to create a tree shape rather than a shrub, remove side branches from the lower part of the tree.