The Cathedral Cactus (Euphorbia trigona) is a striking succulent prized for its architectural form and low-maintenance needs. It is often called the African Milk Tree or Abyssinian Euphorbia, names derived from its Central African origins and the milky sap it produces. This plant features tall, upright, three-sided stems, giving it a unique, candelabra-like appearance. This guide provides instructions for cultivating a healthy Euphorbia trigona in a home environment.
Creating the Ideal Environment
The Cathedral Cactus thrives in a location that mimics its native, hot, and arid habitat. It requires bright, indirect light for optimal growth, but it can tolerate some direct sun, particularly morning sun. Placing the plant near a south- or west-facing window provides the necessary light exposure. Insufficient light causes the stems to become elongated and weak.
This succulent prefers warm conditions, growing best in temperatures ranging from 60°F to 85°F (16°C to 29°C). The plant will struggle if temperatures drop below 50°F (10°C) and will not survive a frost. Keep the Euphorbia trigona away from cold drafts, which can cause sudden temperature stress. The plant is tolerant of low humidity, preferring the drier air typical of most indoor environments.
Soil, Potting, and Hydration Management
Proper soil composition and careful hydration are the most significant factors in successfully growing a Cathedral Cactus. The plant requires a porous, fast-draining substrate to prevent water from lingering around the roots, which is the primary cause of plant death. A commercial cactus or succulent potting mix is an appropriate base, amended with materials like perlite, pumice, or coarse sand to enhance drainage. A common and effective ratio is a 2:1:1 mix of cactus mix, perlite, and coarse sand.
The pot selected for the Euphorbia trigona must have drainage holes to allow excess water to escape completely. Overwatering is a frequent mistake, so the correct technique is to water thoroughly and then allow the soil to dry out completely before watering again. During the active growing season in spring and summer, this may mean watering every week or two. A simple test is to insert a finger about two inches deep into the soil; if it feels dry, the plant can be watered.
Watering frequency must be significantly reduced during the plant’s dormant period in fall and winter. The soil should remain dry for longer periods, often requiring water only once every four to six weeks. This seasonal reduction prevents root rot. Repotting should only be done when the plant has become root-bound, using a container that is only one to two inches larger in diameter than the previous one.
Active Care: Fertilization, Pruning, and Propagation
Fertilization
The Cathedral Cactus benefits from periodic feeding exclusively during its spring and summer growing season. Fertilization should occur about once a month using a balanced liquid fertilizer formulated for succulents or cacti. Dilute the fertilizer to half or quarter strength to prevent root burn or salt buildup. No feeding is necessary during the fall and winter months while the plant is dormant.
Pruning
Pruning is occasionally necessary to manage the plant’s height, maintain its upright shape, or remove damaged stems. Since the Euphorbia trigona can grow quite tall with a shallow root system, pruning helps maintain stability. Use a sharp, sterilized knife or shears to make a clean cut at a joint or near the base of the stem.
Propagation
The simplest method for creating new plants is propagation through stem cuttings. After taking a cutting, set it aside in a dry, shaded area for several days until a protective layer, called a callus, forms over the cut end. Once calloused, the cutting can be planted an inch or two deep in fresh, well-draining succulent soil and watered very sparingly until new roots develop.
Handling the Sap and Troubleshooting Common Issues
All species within the Euphorbia genus produce a white, milky latex sap when damaged, which is a safety concern. This sap contains phorbol esters, which are toxic if ingested and act as severe irritants upon contact with skin or eyes. Direct contact can cause skin rashes and swelling, while eye exposure can lead to intense pain and temporary vision impairment.
Safety protocols require wearing protective gloves and eye protection whenever handling, pruning, or propagating the plant. If the sap touches the skin, wash the area immediately with soap and water. Tools used to cut the plant should be cleaned thoroughly to remove any sticky residue.
Common issues are typically related to watering or pests. Softening stems are a clear sign of overwatering and root rot, requiring an immediate reduction in water and checking the roots for decay. Brown or yellow spots on the stems are often a result of sunburn from overly intense, direct sun exposure. Pests like mealybugs and spider mites can be treated by wiping the area with a cotton swab dipped in rubbing alcohol.