The Genus Acacia
This is a large, variable genus of shrubs and trees. Mostly, they are native to Australia, with additional species Asia and Madagascar. In 2005, the genera Acaciella, Mariosousa, Senegalia and Vachellia were separated from Acacia. Acacias are cultivated around the world but are better known in the southwestern United States than in the Coastal Southeast. Many have attractive, colorful flowers. Some have compound leaves but several species bear phyllodes, expanded leaf stalks (petioles) that function as leaves. Some acacias have spines on the branches but the limbs of the tree species may be trimmed up so the spines are not a threat to passers by.
The bean family, Fabaceae, is one of the largest of the plant families. It is characterized by seed pods that are known to botanists as legumes. This is a large family that includes many important economic crop genera, including peanut (Arachis,) soybean (Glycine,) alfalfa (Medicago) and beans (Phaseolus.) Ornamental garden plants include orchid tree (Bauhinia,) redbud (Cercis,) coral tree (Erythrina,) lupine (Lupinus) and black locust (Robinia.)
I decided that I had to have this plant after seeing one in the New Orleans Botanical Garden. The pendant branches of gray-green to silvery-gray phyllodes are very attractive. It is reported to grow to thirty feet tall. Flowers are yellow. Reportedly, it can produce suckers when the roots are disturbed. This native of dry regions in Australia seems to be a little better known in the American southwest than here in the Coastal Southeast. It is reported to be drought tolerant. Surprisingly, reports from the southwest say that it tolerates heavy clay soils and will survive brief periods of flooding. Another report says that it will tolerate winter lows of 15 degrees F. These reports and the healthy young plant in New Orleans suggest that this attractive plant should be trialed elsewhere in the Coastal Southeast.
Plants may be found in specialty nursery catalogs.
I have a few young plants at the University of North Florida but do not yet have experience to share.
This is a distinctive evergreen shrub from Australia that usually grows to about eight feet tall in the garden but can reach twenty feet tall. Small, triangular, gray-green phyllodes line the stems like oddly-shaped leaves. Branches become somewhat pendant with age. The fragrant, yellow flowers are borne in small balls. It grows well in full sun and requires a well-drained soil. It is reported to be moderately salt tolerant and to grow from zone 9 south but can be found in lower zone 8b. A plant at Armstrong Atlantic State University in Savannah, Georgia survived a windy night in the mid-teens F with some stem die back.
This plant may be found in specialty catalogs. It is propagated by seeds. Reportedly, semi-hardwood cuttings in summer may be rooted.
I have not grown this plant yet but a nice specimen grew for years at the Armstrong Atlantic State University Arboretum. It was killed by two successive cold winters.
This is a spineless evergreen tree from Australia that grows to forty to sixty feet tall. It has an open, generally upright habit, often with somewhat weeping branches. The common name, “shoestring” refers to the long, narrow, pendulous phyllodes. White to yellowish flowers are borne in spherical clusters near the branch tips. The long seed pod is constricted between each round seed. The plant may produce root suckers but not frequently. In nature, it grows along water courses in scrub forest, and can tolerate flooding and high levels of salt in the soil. It is cultivated in irrigated California and Arizona gardens and is particularly attractive in small groves. It is useful in areas where security lights cannot be blocked by dense tree canopies. It is reported to be cold hardy to zone 8b and south. From my observations, this species, especially young trees, should be treated as cold tender in zone 8b.
This plant appears occasionally in local nurseries and may be found in specialty catalogs. Seeds are easy to germinate and seedlings are reasonably fast growing. Reportedly, this plant may be propagated by stem cuttings.
It grows best in a well-drained, sunny site and is drought tolerant in our area. New shoots begin to grow in late March to mid-April, depending on spring temperatures. The plant at my home flowered from June into November in its first year. It survived a brief winter low of 18º F but was killed to the ground by an unusually long, cold winter with a low of the same temperature. Plants have grown well in zone 9a at the University of North Florida in Jacksonville, Florida and I have planted many seedlings in parking lot islands. Occasionally, I lose plants to periods of heavy rain and to high winds.
other Acacia species
An Australia mulga, Acacia aneura, grew well for a few years in a hot, sandy parking lot island at the University of North Florida in zone 9a. It survived droughts but died during a year with normal rains. The gray foliage is attractive and it has no thorns. I will try it again sometime.
Acacia craspedocarpus grows at the Armstrong Atlantic State University Arboretum. It is a shrubby species to eight feet tall or more. The phyllodes are gray-green when mature but are covered with tiny coppery hairs when young. It is thornless
Acacia redolens is supposed to be a rapid grower but these plants grew poorly in a sandy site in zone 9a for a year during a drought. They died the following year during a summer average rainfall. This plant may survive in the right site in the Coastal Southeast but it this experience suggests that it will not be an easy plant for this area.