The Red Cathedral Cactus (Euphorbia trigona ‘Rubra’) is a striking houseplant known for its architectural form and deep reddish coloration. Despite its common name, it is a succulent belonging to the Euphorbia family, not a true cactus. The ‘Rubra’ cultivar is distinguished by its stems and small, teardrop-shaped leaves that develop a vibrant burgundy or ruby-red hue under proper lighting. It exhibits an upright, columnar growth habit with three- or four-sided ribbed stems, eventually forming a dense, shrub-like structure. Native to the arid regions of Central Africa, this plant is well-adapted to dry environments and is a low-maintenance option for indoor gardening.
Ideal Conditions for Growth
The reddish pigment intensifies with exposure to strong light, making placement important for maintaining color. This plant thrives in bright, indirect light for most of the day, requiring several hours of high intensity light. While it tolerates some direct sun, intense afternoon sunlight should be avoided, especially in warmer months, as it can scorch the stems. Insufficient light causes the plant to stretch and thin out (etiolation), and the vibrant red tones will fade to a duller green.
The Red Cathedral Cactus prefers warm, stable temperatures, ideally ranging between 65°F and 85°F (18°C to 29°C) during active growth. It is not tolerant of cold; temperatures below 50°F (10°C) can cause significant damage. Keep the plant away from drafts from windows or vents, particularly during the winter, as sudden temperature drops cause stress. Average household humidity levels are acceptable, and supplemental misting is unnecessary, as the plant is suited to dry indoor air.
Proper Potting and Soil Selection
The soil must prioritize rapid water movement to prevent the root system from remaining saturated. A commercial cactus or succulent potting mix provides a good base, but it should be amended with materials like perlite, pumice, or coarse sand to increase aeration and drainage. A well-performing mixture combines standard succulent mix with an equal part of inorganic material. Avoiding water-retentive soils is essential for preventing root rot.
The container must include a functional drainage hole to allow excess water to escape completely. Porous materials like terracotta or unglazed ceramic are preferred because they help wick moisture away from the soil and allow it to evaporate more readily. Since the plant grows tall and can become top-heavy, select a sturdy, wide-bottomed pot to provide stability and prevent tipping.
Repotting is infrequent, typically necessary only every two to three years or when the plant is visibly rootbound. The process is best performed in the spring or early summer, aligning with the beginning of its active growing cycle. When repotting, only increase the container size slightly, choosing a pot that is just one size larger than the previous one. This prevents excess soil volume that might retain too much moisture.
Routine Watering and Feeding Schedule
Improper watering is the most common failure point in caring for this plant. Use the “soak and dry” method: thoroughly saturate the soil until water runs from the drainage hole, then allow the soil to dry out completely before watering again. The plant stores water in its fleshy stems, making it highly drought-tolerant and more susceptible to overwatering than drying out.
Watering frequency depends on environmental factors, including temperature, light exposure, and the season. During the active growing period of spring and summer, watering may occur every two to four weeks, depending on how quickly the soil dries. As light decreases and temperatures cool in fall and winter, growth slows, and watering must be significantly reduced or stopped entirely to prevent root disease. If water is necessary in cooler months, limit it to a small amount once a month or less.
Observing the plant provides the best indication of its water needs. Soft, mushy stems or a yellowing color indicate overwatering and the onset of root rot. Conversely, if the stems begin to shrivel slightly or the leaves drop excessively, the plant requires hydration. Adjusting the watering schedule promptly based on these visual cues maintains plant health.
The Red Cathedral Cactus benefits from minimal fertilization, applied only during the spring and summer growth phase. Dilute a balanced, water-soluble fertilizer (such as a 20-20-20 or cactus-specific formula) to one-quarter or half strength before application. Feeding once per month during the growing season provides sufficient nutrients without promoting weak growth. Suspend fertilization completely in the fall and winter to avoid mineral salt accumulation, which can damage the roots.
Propagation and Common Issues
Propagation is most easily accomplished using stem cuttings taken from the main plant. When taking a cutting, wear protective gloves and safety glasses because all Euphorbia species exude a milky white sap, known as latex, when wounded. This latex is a toxic irritant that can cause skin rashes and eye damage. The cutting should be set aside in a dry, well-ventilated area for several days to allow the cut end to dry and form a protective, hardened layer called a callus.
Once the callus has formed, the cutting can be planted in a well-draining succulent mix to develop roots. Water the newly planted cutting sparingly until a root system is established, which can take several weeks. The plant is generally resistant to most pests, but it can occasionally be affected by mealybugs or scale insects. Treat these pests by gently dabbing them with a cotton swab soaked in isopropyl alcohol, which desiccates the insects upon contact.
The most persistent problem for this succulent remains root rot, a fungal disease caused by consistently waterlogged soil. Prevention relies on using fast-draining soil and strictly adhering to the “soak and dry” watering schedule. If the plant shows advanced signs of mushy, discolored stems, the affected sections must be promptly removed to prevent the spread of the rot.