Euphorbia trigona aka African Milktree

Euphorbia trigona is a columnar succulent. Indoors it typically reaches around 1.5–2 metres (5–6 ft) tall with a narrow spread of roughly 0.5–1 metre, while outdoor plants in frost-free regions can reach 3–4 metres (up to about 12 ft) over many years. Reported growth rates vary — RHS calls it slow-growing (10–20 years to ultimate height), while NC State describes it as rapid in ideal warm, sunny conditions.

Euphorbia trigona is a tender tropical succulent that prefers typical warm room temperatures and should be kept above about 5°C (41°F). The RHS gives it a hardiness rating of H2, meaning it tolerates low temperatures from roughly 1–5°C but will not survive frost, and Wikipedia notes it can withstand only brief dips to around -3°C (27°F). Keep it well away from cold drafts and unheated windows in winter.

Euphorbia trigona very rarely flowers in cultivation, and most houseplant specimens never bloom at all — the plant is believed to be of hybrid origin and flowers are seldom produced. When mature plants do flower, RHS and NC State describe small, insignificant pale-green to yellowish cyathia produced at the tops of the stems in spring and summer. Indoors, expect foliage interest only.

The most commonly offered cultivar is Euphorbia trigona f. rubra (often sold as 'Royal Red'), which develops deep burgundy to reddish-purple stems and leaves, especially in bright light, rather than the species' plain green. RHS maintains a dedicated page for the rubra form, and NC State and the University of Arizona both list the Royal Red cultivar. Both share the same three-sided stems, paired spines, and care requirements.

Euphorbia trigona can only be grown outdoors year-round in frost-free climates, roughly USDA zones 10–11, where it is used as a specimen plant or hedge. In temperate regions the RHS rates it H2, so it must be kept as a houseplant or conservatory specimen and only moved outside during warm summer weather. Plant in sharply drained, sandy soil in full sun to part shade, and bring it back indoors before night temperatures drop below about 5°C.

Prune Euphorbia trigona only when necessary to control height or remove damaged branches, cutting stems cleanly with a sharp, clean knife at a branch junction. Always wear gloves and eye protection, because the milky latex sap is an irritant that can cause severe skin and eye reactions, and is harmful if ingested. The RHS recommends dipping cut surfaces in charcoal or lukewarm water to stop the latex bleeding and help the wound seal.

Euphorbia trigona roots readily from stem cuttings taken in spring or early summer. Cut a healthy side branch with a clean knife, rinse or dip the cut end in lukewarm water (or charcoal) to stop the latex bleeding, then let the cutting dry in a warm, shaded spot for 3–7 days so a callus forms. Once calloused, insert the cutting into gritty, well-drained cactus compost and water sparingly until roots establish. Always wear gloves and eye protection, as the sap is a strong irritant.

Yellowing leaves on Euphorbia trigona are most often a sign of overwatering and the root rot that follows in soggy soil. As a succulent native to arid parts of Central Africa, it stores water in its stems and should only be watered when the top 1–2 inches of soil feel dry. Using a well-drained, sandy or cactus mix and easing off water in winter usually resolves the problem.

Brown, mushy patches usually indicate rot from excess moisture or cold damage, while dry brown edges on the small teardrop leaves typically mean sunburn or underwatering. Euphorbia trigona grows best between 65–85 °F in bright indirect light, and should be moved indoors before temperatures drop below 45 °F. Let the soil dry between waterings and avoid sudden moves from shade into intense direct sun to prevent scorching.

Euphorbia trigona has a notably shallow, small root system and its tall candelabra-like stems are prone to falling over or leaning as the plant matures. Soft, drooping stems can also signal root rot from overwatering, which weakens the base of the plant. Repotting into a heavier, well-drained container and staking or supporting tall specimens usually corrects the problem.

The small teardrop leaves of Euphorbia trigona are naturally short-lived and are dropped seasonally, especially in cooler or drier conditions as the plant enters dormancy. The succulent stems are the main photosynthetic organs, so leaf loss is rarely a cause for alarm. Sudden wholesale leaf drop, however, can also indicate stress from overwatering, cold drafts, or a big change in light.

In ideal conditions Euphorbia trigona can be a rapid grower, so slow growth usually points to too little light, cool temperatures, or winter dormancy. It performs best in bright light, temperatures between 65–85 °F, and a well-drained cactus mix watered only when the top inch of soil is dry. Expect growth to slow markedly in winter and resume once warmth and longer days return.

The main disease of Euphorbia trigona is root rot caused by overwatering or poorly drained soil, which can also lead to other fungal problems. Common insect pests to monitor for are mealybugs, aphids, and spider mites — all typical of cacti and succulents grown as houseplants. Good air circulation, a gritty well-drained mix, and inspecting stems and leaf axils regularly are the best prevention.

No — Euphorbia trigona is not edible and should be considered toxic. All parts of the plant contain a milky latex with diterpenoid euphorbol esters; ingestion can cause severe gastroenteritis, vomiting, diarrhea, and even convulsions. The sap is also caustic on skin and is a medical emergency if it gets in the eyes.

In traditional African medicine, Euphorbia trigona has been used for wound healing, wart treatment, and as an anti-inflammatory, and it has also been investigated for cytotoxic and anticancer activity in modern phytochemical research. These uses rely on compounds in the latex, which is itself highly caustic and can cause severe skin blistering and eye injury. Self-treatment is not safe — the same latex responsible for any medicinal effect readily causes burns, dermatitis, and, on eye contact, potential blindness.

Euphorbia trigona is most widely grown as an ornamental houseplant or accent specimen, prized for its upright, candelabra-like stems. In frost-free climates such as parts of Central Africa it is also planted as a living hedge, and in Gabon it has been used as a ritual plant and for preparing arrow and fish poisons. Its sharp spines and caustic latex mean it works well as a boundary plant but a poor choice around children or pets.