Euphorbia mammillaris
| Light | Bright light to gentle full sun; a little more colour on the variegate with strong light |
|---|---|
| Water | Sparingly; let the soil dry fully between waterings, dry rest in winter |
| Soil | Fast-draining mineral mix (see Soil and potting mix) |
| Temperature | Keep above freezing; USDA zones 9b–11 |
| Propagation | Cuttings (easy); also offsets and seed |
| Toxicity | Toxic; the milky latex irritates skin, eyes and mouth (see below) |
Euphorbia mammillaris is a clumping, ribbed succulent from the Cape region of South Africa, widely grown for its neat, geometric columns that look remarkably like little cobs of corn — hence the common names corn-cob euphorbia and Indian corn cob. It belongs to the vast genus Euphorbia and, like its relatives, is not a cactus despite the resemblance; it is best known in cultivation through its blushing pink-and-cream variegated form.
Description
Euphorbia mammillaris forms low, branching clumps of short, upright stems, each stem a stout cylinder divided into (usually) seven to seventeen knobbly ribs. The tubercles along those ribs give the surface its characteristic corn-cob texture. Stems are a soft grey-green, and scattered short, blunt, pale spines — actually persistent, sterile flower stalks rather than true spines — stud the ridges.
The plant is dioecious, carrying tiny cyathia (the specialised euphorbia "flowers") near the stem tips. Like all euphorbias it bleeds a white, milky latex when cut or bruised, and this sap is an irritant to be handled with care.
The popular variegated form, often sold as Euphorbia mammillaris ‘Variegata’, loses much of its green pigment and flushes soft cream, pink and rose, deepening to bright pink in strong light and cool weather. Because it has little chlorophyll it grows more slowly and is a touch more delicate than the plain green species.
Distribution and habitat
The species is native to the Cape region of South Africa, ranging from the Western Cape eastward into the Eastern Cape, where it grows in dry, open scrub and on stony ground, often forming spreading colonies among low shrubs. It is adapted to a semi-arid climate with a long dry season, which is why it resents sitting wet in cultivation.
Cultivation
Euphorbia mammillaris is one of the easier succulent euphorbias and a good choice for a beginner who is comfortable with the group's caustic sap. Grow it in a very free-draining, mostly mineral mix and give it bright light — the green form is happy in gentle full sun, while the variegate colours up best with strong light but appreciates a little shielding from the fiercest afternoon rays to avoid scorching its pale skin.
Water thoroughly once the soil has dried out completely, then let it dry again; through winter keep the plant nearly dry and cool but frost-free. Overwatering, especially in a heavy mix or a pot without drainage, is the usual cause of rot and loss. Repot infrequently, in the warmer months, and see Watering and Repotting for general technique.
Always wear gloves and eye protection when cutting or handling damaged stems, and keep the plant out of reach of children and pets.
Propagation
Stem cuttings are the standard and easiest method. Take a healthy stem or branch, then dip the cut end in cool water or blot it to stop the latex flow, and let the cutting callus for several days to a week before setting it in a dry, gritty mix to root. The plant also branches freely, so rooted offsets can be separated from the clump; seed is possible but less common in the hobby. See Propagation — cuttings and Propagation — offsets for full walkthroughs.
Note that variegated cuttings must be taken from stems that carry enough colour and enough green to survive — an all-pink shoot has too little chlorophyll to root and grow on its own.
Common problems
- Caustic latex — the milky sap is a skin, eye and mucous-membrane irritant and is toxic if ingested. Wear gloves, avoid touching your face, and wash off any sap promptly.
- Rot — from overwatering or a slow-draining mix; stems soften, discolour and collapse, usually from the base.
- Etiolation — too little light makes stems stretch, thin and lose their tidy ribbed shape; the variegate also loses its pink flush.
- Sunburn — the pale variegated form can scorch if moved abruptly into intense sun; acclimatise it gradually.
- Pests — mealybugs (white fluff between the ribs and at the roots) and spider mites are the usual offenders. See Pests and diseases.
See also
- Euphorbia — the genus overview
- Propagation — cuttings · Propagation — offsets · Soil and potting mix · Watering · Repotting · Pests and diseases