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Lost Crops of Africa: Fruits, Volume III
accepts a variety of exposures including full sun and fairly heavy shade. In shade it tends toward taller growth.
Rainfall Although native to coastal areas with annual rainfall of about 1,000 mm, the plant is drought-resistant and requires no watering in summer rainfall areas. As noted earlier, it has reasonable drought tolerance.
Altitude Unreported, but in Swaziland, it reaches about 1,000 m. A likely upper limit for good growth is 1,500 m.
Low Temperature The carissa grows where temperature rarely falls below freezing. Well-established plants can, however, survive −5°C relatively unscathed. Young plants need protection when the temperature drops to about zero.
High Temperature The upper limit is unknown but during summer in Pretoria it survives temperatures up to 32°C (in the shade). Best growth is obtained in full sun.
Soil The plants are not exacting in soil requirements. Almost any substrate, limestone heavy clay to sand, is fine as long as it drains well.
Salinity Carissa is quite salt tolerant. For irrigation purposes, water of 8 mmho conductivity (about 5,000 ppm) is acceptable. As mentioned, it withstands salty spray, making it a good choice for coastal gardens.
Generally speaking, Carissa species in Africa occur in two vast belts from Senegal to Sudan, and from Ethiopia to South Africa. These, too, produce edible fruits. At this stage, they remain undeveloped and the fruits seem less tasty then the species from Natal. As noted, however, C. haematocarpa may have special potential in drier areas, and C. bispinosa at altitude. A few Carissa species are also found in Europe, Asia, and Australia. Though C. macrocarpa currently seems most promising as a potential cultivated crop, the others deserve exploratory research and testing.