Culture
Winter hardy in frost-free USDA Zones 10-11 where plants are best grown in well-drained soils in full sun to part shade. Must have sharply-drained soils. Water consistently in summer, but allow soils to dry out after each watering. Decrease watering in winter. Plants are intolerant of frost. Potted plants may be overwintered indoors. May be grown as a houseplant.
Noteworthy Characteristics
Euphorbia trigona, commonly called African milk tree, is an upright, shrubby, branching succulent native to central Africa where it typically grows in seasonally dry tropical forests. It is widely cultivated in warm, tropical, subtropical, and arid regions an ornamental plant, and around the world as a houseplant. This species has escaped cultivation in India where it grows in disturbed areas and roadsides, forming thickets and spreading mostly vegetatively though fallen stem fragments. Mature plants can reach up 6-12' tall with a stout, cylindrical, grey trunk and fleshy, 3-5 sided branches. Small, sharp spines and ovate leaves are held along the sides and tops of the stems. The leaves are dropped seasonally. Small, inconspicuous flowers are produced seasonally by mature specimens, but they are not considered horticulturally significant and plants in cultivation rarely flower.
Genus name probably honors Euphorbus, physician to the King of Mauretania.
The specific epithet trigona means "three-angled" or "triangular", in reference to the mostly three-sided stems of this species.
The common name African milk tree refers in part to the native range of this species as well as the milky white sap exuded from cut stems which is typical of euphorbs.
Problems
Root rot will occur in overly moist soils. Watch for aphids, mealybugs, and spider mites. Skin and eye irritation can result from contact with the milky sap.
Uses
Where winter hardy, this euphorbia is used as a specimen, hedge or container plant. May be grown indoors as a houseplant.