Euphorbia horrida
| Light | Bright light to full sun |
|---|---|
| Water | Moderately in the growing season; keep dry and cool in winter |
| Soil | Fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; USDA zones 9b–11 |
| Propagation | Cuttings and offsets; seed |
| Toxicity | Toxic — the milky latex irritates skin and eyes and is harmful if swallowed |
Euphorbia horrida is a robust, gray-green ribbed succulent from South Africa that grows into a stout column and is armed with stout spines, giving it the look of a barrel cactus — though it is a true Euphorbia, not a cactus at all. Its convincing resemblance to a spiny barrel cactus has earned it the common name African milk barrel, and it is a classic example of the way euphorbias and cacti have evolved similar forms on different continents.
Description
Euphorbia horrida forms a solid, cylindrical to barrel-shaped body that is usually gray-green to bluish-green and marked by numerous prominent vertical ribs. Along the edge of each rib sits a row of hardened, spine-like structures. In this species the "spines" are in fact persistent, woody flower stalks (peduncles) rather than true spines, but they function much the same way, protecting the plant and giving it its formidable, cactus-like armour. They can be reddish-brown when young, ageing to gray.
Plants are usually solitary when young but tend to cluster with age, forming a mound of several heads from the base. Like many succulent euphorbias, it is dioecious — individual plants are either male or female — and bears small, unshowy flowers (technically cyathia) near the top of the ribs, often flushed dark red or purple. As with every Euphorbia, the plant is filled with a milky white latex that flows freely when the tissue is cut or damaged.
Distribution and habitat
The species is native to the Great Karoo region of the Eastern and Western Cape provinces of South Africa, where it grows in arid, rocky scrubland. It is well adapted to a harsh, dry climate with hot days, cool nights and low, seasonal rainfall, often growing among rocks and low shrubs that provide a little shelter. Several forms and varieties occur across its range, varying in colour, rib count and the length of the spine-like peduncles.
Cultivation
Euphorbia horrida is one of the easier columnar euphorbias to grow and a good choice for someone moving beyond beginner succulents. Grow it in a very free-draining, mostly mineral mix in a pot with a generous drainage hole, and give it as much bright light as you can — it colours up best and stays compact in strong sun, whereas too little light makes it etiolate and lose its barrel shape.
Water moderately through the warm growing season, letting the mix dry out between waterings, then keep the plant dry and cool through winter to prevent rot. It tolerates heat well but resents cold, wet conditions; protect it from frost. See Watering and Repotting for general technique.
A word of caution: the milky latex is toxic and can cause painful skin and eye irritation. Wear gloves, keep it away from your face, and wash any sap off promptly when handling, pruning or taking cuttings. See Pests and diseases for troubleshooting.
Propagation
Euphorbia horrida is readily propagated from offsets or stem cuttings taken from clustering plants, and can also be grown from seed. Cuttings bleed copious latex when severed — dip the cut end in water or blot it to stop the flow, then let the cutting callus for several days to a week in a dry, shaded spot before setting it in dry, gritty mix to root. Handle all cuttings with gloves.
Seed is the usual route for producing large numbers of plants and for maintaining variety, but because the species is dioecious you need both a male and a female plant to set viable seed. See Propagation — cuttings, Propagation — offsets and Propagation — seed for full walkthroughs.
Common problems
- Rot — the most common cause of loss, almost always from overwatering, a slow-draining mix, or cold, damp winter conditions; the body softens and discolours from the base.
- Etiolation — too little light makes the plant stretch, pale and lose its stout barrel form.
- Pests — mealybugs (white fluff between the ribs and at the roots) and spider mites are the usual culprits; watch the base and root zone closely.
- Latex irritation — not a plant problem but a grower one: always protect skin and eyes when cutting or handling this species.
See also
- Euphorbia — the genus overview
- Soil and potting mix · Watering · Repotting · Propagation — cuttings · Propagation — offsets · Pests and diseases