Euphorbia grandicornis
| Light | Bright light to full sun once established |
|---|---|
| Water | Moderately in the warm months; keep dry and rested in winter |
| Soil | Fast-draining, gritty succulent mix (see Soil and potting mix) |
| Temperature | Warmth-loving; keep above about 10 °C, USDA zones 10–11 |
| Propagation | Stem cuttings; also seed |
| Toxicity | Toxic — irritant milky latex; keep away from pets and children |
Euphorbia grandicornis, commonly called the cow's horn or cow's horn euphorbia, is a spiny, shrubby succulent from southeastern Africa grown for its dramatic, deeply constricted stems. Its three-winged branches pinch in at regular intervals and zig-zag as they grow, each wavy margin armed with large, paired, horn-like grey spines that give the plant both its name and its unmistakable silhouette.
Description
Euphorbia grandicornis is a much-branched succulent that forms a sprawling, candelabra-like shrub, often to a metre or more in cultivation and larger in habitat. The stems are green, three-angled (occasionally four) and strongly segmented: each new section swells and then constricts sharply at the joint, so the branches appear to be built from a stack of separate horn-shaped units. This repeated pinching, combined with the way the plant angles at each segment, gives it a distinctly jointed, zig-zag look.
Along the wavy, horny margins of each wing sit paired spines that broaden at the base and can reach several centimetres long — the "horns" of the common name. Like other members of the genus, the plant carries a milky white latex that bleeds freely from any wound. Small yellow flower structures (cyathia) appear along the ridges in the growing season, followed by little three-lobed fruits; the true flowers are tiny and typical of Euphorbia.
Distribution and habitat
The species is native to southeastern Africa, occurring in South Africa (KwaZulu-Natal and the northern provinces), Eswatini and Mozambique. It grows in hot, seasonally dry bushland and thicket, typically in well-drained ground among rocks and other thorny shrubs, where its own formidable spines and branching habit help it form impenetrable clumps.
Cultivation
Euphorbia grandicornis is an undemanding grower where it can be kept warm and dry in winter. Plant it in a very free-draining, gritty mix in a pot that will support its top-heavy, sprawling growth, and give it bright light to full sun to keep the stems compact and well-coloured. Water moderately while it is actively growing in the warm months, always letting the mix dry out between soakings, and reduce watering to almost nothing through the cool season — cold, wet roots are the quickest route to rot.
Protect the plant from frost; it resents temperatures much below about 10 °C. When handling, pruning or repotting, take care with both the long spines and the irritant latex (see Common problems below). See Watering for general technique.
Propagation
The usual method is by stem cuttings. A segment or branch is cut cleanly, and the flow of latex is stopped — many growers rinse or dab the cut and then let the piece callus in a dry, shaded spot for several days before planting it in a barely-moist gritty mix. Rooting is quickest in warm weather. The species can also be raised from seed where it is available. See Propagation — cuttings and Propagation — seed for full walkthroughs; wear gloves and eye protection whenever you cut the plant.
Common problems
- Rot — the commonest killer, almost always from overwatering or a poorly-draining mix, especially in cool weather; affected stems soften, discolour and collapse at the joints.
- Cold damage — exposure to frost or prolonged chill causes corky scarring or blackened, mushy tissue.
- Latex irritation — the milky sap is a skin and eye irritant and is toxic if ingested; wash off any contact promptly and keep it away from your face, pets and children. This is a handling hazard rather than a disease, but it is the problem most new growers underestimate.
- Pests — mealybugs (white fluff in the joints and around the spines) and, in dry indoor air, spider mites are the usual offenders. See Pests and diseases.
See also
- Euphorbia — the genus overview
- Soil and potting mix · Watering · Propagation — cuttings · Propagation — seed · Repotting · Pests and diseases