Introduction

This tall, semi-evergreen, native shrub or small tree has feathery, finely divided leaflets of a soft, medium green color. The slightly rough stems are a rich chocolate brown or grey, and possess long, sharp, multiple thorns. The small, bright yellow, puff-like flowers are very fragrant and appear in clusters in late winter then sporadically after each new flush of growth, providing nearly year-round bloom. The persistent fruits have a glossy coat and contain seeds which are cherished by birds and other wildlife.

General Information

Scientific name: Vachellia farnesiana

Pronunciation: Va-KEL-lee-a far-nee-zee-AY-nuh

Common name(s): sweet acacia, Huisache

Family: Fabaceae or Leguminosae

USDA hardiness zones: 9A through 11 (Figure 2)

Origin: the original range is uncertain but is thought to be tropical America

UF/IFAS Invasive Assessment Status: not considered a problem species at this time, may be recommended

Uses: specimen; street without sidewalk; container or planter; reclamation; highway median; bonsai

Description

Height: 15 to 25 feet

Spread: 15 to 25 feet

Crown uniformity: irregular

Crown shape: vase, round, spreading

Crown density: open

Growth rate: slow

Texture: fine

Foliage

Leaf arrangement: alternate (Figure 3)

Leaf type: bipinnately compound, even-pinnately compound; made up of pairs of 2 to 6 primary leaflets and 10 to 25 secondary leaflets

Leaf margin: entire

Leaf shape: linear

Leaf venation: pinnate

Leaf type and persistence: semi-evergreen

Leaf blade length: 1 to 4 inches; secondary leaflets are ½ inches

Leaf color: medium green

Fall color: no color change

Fall characteristic: not showy

Flower

Flower color: bright yellow

Flower characteristics: very showy; fragrant; emerges in clusters on globe-shaped heads that hang from 2-3" long stalks

Flowering: primarily late winter, but also year-round

Fruit

Fruit shape: pod or pod-like, elongated; cylindrical

Fruit length: 2 to 3 inches

Fruit covering: dry or hard

Fruit color: purplish-red

Fruit characteristics: attracts birds; showy; fruit/leaves not a litter problem

Trunk and Branches

Trunk/branches: branches droop; showy; typically multi-trunked; thorns

Bark: olive green and smooth, becoming gray brown, furrowed, and scaly

Pruning requirement: needed for strong structure

Breakage: resistant

Current year twig color: brown

Current year twig thickness: thin

Wood specific gravity: unknown

Culture

Light requirement: full sun

Soil tolerances: clay; sand; loam; acidic; alkaline; well-drained to occasionally wet

Drought tolerance: high

Aerosol salt tolerance: moderate

Other

Roots: not a problem

Winter interest: no

Outstanding tree: no

Ozone sensitivity: unknown

Verticillium wilt susceptibility: resistant

Pest resistance: free of serious pests and diseases

Use and Management

It can be trained into a tree for use in median strips, or can be used as a street tree where there is not a need for tall-vehicle clearance beneath the crown. The small stature and low, spreading branching habit makes pruning for vehicular clearance difficult unless it is properly trained from an early age. But the required input of man hours for early training may be offset by the high drought, pest, and insect resistance of the tree. Do not locate the tree too close to where people can be injured by the sharp thorns on the branches.

Although easy to grow in any acid or alkaline soil, including clay, the leaves will drop if the soil is allowed to dry out. This drought avoidance mechanism allows the plant to grow well with no irrigation, once established. Growing best in full sun, this thorny, well-branched shrub makes an excellent barrier planting or nesting cover for wildlife. When trained as a small tree and used as a freestanding specimen, it is likely to provide a source for comments, such as "What's that?" But its growth rate is extremely slow, making it unpopular in the nursery trade but popular with those who care for it in the landscape. Sweet acacia has its place in any sunny shrub border or as an accent plant in any garden if located away from areas where children frequent, since the thorns can inflict severe pain. It is well suited for dry climates with little rainfall.

Propagation of sweet acacia is by seeds or cuttings.

Pests and Diseases

No pests or diseases are of major concern. Occasionally anthracnose can infect leaves.

References

Koeser, A. K., Hasing, G., Friedman, M. H., and Irving, R. B. 2015. Trees: North & Central Florida. University of Florida Institute of Food and Agricultural Sciences.

Koeser, A.K., Friedman, M.H., Hasing, G., Finley, H., Schelb, J. 2017. Trees: South Florida and the Keys. University of Florida Institute of Food and Agricultural Sciences.