Euphorbia trigona (African Milk Tree)

Euphorbia trigona, commonly known as the African Milk Tree or Cathedral Cactus, is a visually striking, fast-growing plant often mistaken for a cactus due to its tall, spiny, and columnar appearance. This resilient succulent is a popular choice for both indoor and outdoor gardens due to its low-maintenance care, architectural form, and tolerance for various conditions.

Euphorbia is a member of the spurge family (Euphorbiaceae), which also includes the popular poinsettia, croton, crown of thorns, castor bean plant, or Copperleaf.

Description

The African Milk Tree features tall, upright stems that are triangular in cross-section, hence its species name “trigona.” The plant has green stems with ridged edges adorned with rows of small, sharp thorns. Each ridge also has small, teardrop-shaped leaves that grow intermittently, adding a touch of softness to the otherwise spiny appearance. The plant’s stems are often patterned with lighter and darker shades of green, creating a beautiful contrast.

In some cultivars, such as Euphorbia trigona ‘Rubra’, the stems and leaves take on a reddish or burgundy hue, further enhancing the plant’s ornamental appeal. Over time, the plant develops multiple branches, giving it a dense, bush-like form.

Native Habitat

The African Milk Tree is native to the central regions of Africa, particularly in countries like Angola, Gabon, and Congo. In its native habitat, it thrives in hot, arid environments and is well-adapted to endure long periods of drought. Its natural ability to store water in its fleshy stems allows it to survive in areas where rainfall is scarce.

Plant Type and Habit

Although its appearance resembles a cactus, Euphorbia trigona is a succulent and not a true cactus. The plant is a perennial that grows upright with a branching habit, and its fast-growing nature allows it to develop into an impressive specimen quickly.

In terms of habit, it forms a vertical, columnar structure with multiple branching stems and a stout, cylindrical, grey trunk. This upright growth habit makes it ideal for filling vertical space in both indoor and outdoor settings.

Plant Size

In its natural habitat, the African Milk Tree can grow up to 6-12 feet (1.8 to 3.6 meters) tall and 5-10 feet (1.5 to 3 meters) wide.

Flowers

The African Milk Tree is primarily grown for its stunning form and not for its flowers, as it rarely blooms in cultivation, particularly when grown indoors. When it does flower, the blooms are small, inconspicuous, and yellow or white. They emerge at the tips of the branches, but flowering is uncommon, especially outside its natural habitat.

If grown in ideal conditions and if the plant does bloom, it typically produces flowers in the summer months. However, as previously mentioned, it is rare to see flowers on this plant in cultivation, particularly when grown indoors.

Foliage

The plant’s most striking feature is its triangular stems, which grow upright and columnar. The stems are fleshy and green, with ridged edges adorned by short, sharp spines. These spines grow in pairs along the ridges and typically measure about 1/4 inch (5 mm) in length.

The ridges of the stems also produce small leaves, which are oval or teardrop-shaped. These leaves are green in color, although they may take on a reddish hue in certain varieties. While the leaves are not long-lasting, they add an element of texture and color to the plant when present.

Hardiness

The African Milk Tree is hardy in USDA zone 9-11 and can tolerate temperatures down to 27°F (-3°C) for short periods. However, it thrives best in warmer climates with temperatures ranging from 65°F to 85°F (18°C to 29°C). In regions with cold winters, the plant should be grown indoors or brought inside during the colder months, as it is not frost-tolerant.

Uses

The African Milk Tree is widely used as an ornamental plant, both indoors and outdoors. Its upright, columnar structure makes it an excellent addition to:

• Indoor plant collections: It works well in bright, sunny spaces like living rooms, offices, or sunrooms.
• Outdoor landscaping: In warmer climates, it can be grown as a dramatic focal point in gardens or rock gardens.
• Containers: Due to its narrow growth habit, it is well-suited for growing in pots, making it easy to move and place in various spaces.

Additionally, the plant’s rapid growth and ability to branch make it a popular choice for creating privacy screens or natural fences in outdoor settings.

Wildlife

Euphorbia trigona may attract insects and small birds in its natural habitat, although it is not particularly known for supporting a wide range of wildlife. Its flowers, if produced, may attract pollinators, but this is relatively rare in cultivated plants.

Toxicity

One important aspect of the African Milk Tree is its toxicity. Like other Euphorbia species, this plant produces a milky white sap when its stems or leaves are damaged. This sap is toxic and can cause skin irritation, rashes, or blistering if it comes into contact with the skin. It is also harmful if ingested, making the plant toxic to humans and pets. When handling the plant, it’s important to wear gloves and wash your hands afterward.

Deer and Rabbits

Thanks to its spiny structure and toxic sap, the African Milk Tree is generally resistant to deer and rabbits.

Drought Tolerance

Euphorbia trigona is highly drought-tolerant due to its succulent nature. Its fleshy stems are capable of storing water, allowing the plant to survive long periods without moisture.

Invasiveness

The African Milk Tree can potentially become invasive in certain regions. It has become naturalized in places like Cuba and India, where it grows in disturbed sites and abandoned gardens, forming dense thickets in dry and semiarid areas. The plant spreads primarily through vegetative reproduction, with cuttings and stem fragments easily taking root and establishing new plants. This ability to spread aggressively in certain climates makes it a species to monitor closely, especially in non-native regions.

Benefits

The primary benefits of growing Euphorbia trigona include its architectural beauty, drought tolerance, and ability to thrive with minimal care. Its rapid growth and vertical habit make it an excellent plant for filling vertical spaces or adding height to indoor and outdoor landscapes.

Additionally, the plant is low-maintenance and can be easily pruned to control its size and shape, making it an ideal choice for busy gardeners or those looking for a statement piece in their plant collection.

How to Grow and Care for an African Milk Tree

The African Milk Tree is a striking succulent popular for its upright, architectural form and ability to thrive in both indoor and outdoor environments. It’s known for its rapid growth, drought tolerance, and minimal care requirements, making it an excellent choice for beginner and experienced gardeners.

Light Requirements

The African Milk Tree thrives in bright, indirect sunlight, but it can also tolerate direct sunlight in the morning or late afternoon. When grown indoors, placing it near a south—or west-facing window is ideal, as it can get ample light throughout the day. Rotate the plant regularly to ensure even growth, as it tends to grow toward the light.

Outdoors, it can handle full sun, but in very hot climates, it should be shielded from the harsh midday rays, as too much intense light can cause sunburn on the stems.

Soil Requirements

As a succulent, the African Milk Tree requires well-draining soil to prevent root rot. A commercial cactus or succulent mix is ideal. You can also create your own mix by combining potting soil, perlite, and sand for better drainage. The key is to avoid water-retentive soils, as the roots of this plant are prone to rotting in waterlogged conditions.

Ensure your pot has drainage holes to allow excess water to escape and prevent soggy soil.

This plant grows best with a soil pH of 6.1 to 7.8.

Watering Schedule

The African Milk Tree is highly drought-tolerant, but proper watering is essential to keep it healthy. Water thoroughly, but make sure the soil dries out completely between waterings. Overwatering is one of the most common mistakes with this plant, leading to root rot and other issues.

• Growing Season (Spring and Summer): Water approximately weekly, allowing the soil to dry out between waterings.
• Dormant Season (Fall and Winter): Reduce watering to once every 4-6 weeks or when the soil is completely dry.
• Tip: It’s better to underwater than overwater this succulent. The plant stores water in its fleshy stems, allowing it to survive extended periods without moisture.

Temperature and Humidity

The African Milk Tree prefers warm temperatures and can thrive in conditions ranging from 65°F to 85°F (18°C to 29°C). While it can tolerate brief drops in temperature, it is not frost-hardy and should be protected from temperatures below 40°F (4°C). In colder climates, it’s best to bring the plant indoors during the winter months.

As for humidity, this plant prefers low to moderate humidity and is well-adapted to dry air. There is no need to mist the plant, and it performs well in typical household conditions.

Fertilizing

African Milk Trees benefit from occasional feeding during the growing season, but they don’t require much fertilizer. Use a balanced, low-nitrogen fertilizer or a cactus-specific fertilizer to encourage healthy growth.

• Fertilizing Schedule: Fertilize once a month during the growing season (spring and summer), diluting the fertilizer to half strength.
• Dormant Season: Do not fertilize the plant during fall and winter when it’s not actively growing.
• Too much fertilizer can cause leggy growth or root damage, so stick to the recommended amounts.

Pruning and Shaping

Pruning an African Milk Tree is important because the plant can grow very tall while having a shallow root system, making it prone to becoming top-heavy or even toppling over.

Regular pruning is necessary to maintain stability and prevent the plant from falling. Always wear gloves to protect yourself from the toxic sap when pruning, and use a sharp, sterilized knife to make clean cuts.

Focus on pruning evenly on both sides of the plant to avoid creating an imbalanced load that could cause the plant to lean or pull out of the soil. After pruning, the cuts will naturally callous over, helping the plant heal and continue growing in a stable, healthy manner.

Overwintering

To overwinter the African Milk Tree, move it indoors before temperatures drop below 40°F (4°C), as it is not frost-tolerant. Place it in a location with bright, indirect light and maintain room temperatures between 60°F to 75°F (16°C to 24°C).

Reduce watering significantly, allowing the soil to dry out completely between waterings. Avoid fertilizing during winter, as the plant enters a dormant period. Ensure good air circulation and keep it away from cold drafts to prevent stress.

Propagating African Milk Tree

Propagating an African Milk Tree is a straightforward process, primarily done through stem cuttings. Follow these steps for successful propagation:

Choose a Healthy Stem: Select a healthy, strong stem from the plant. Look for a mature, non-damaged section that’s firm and upright.

Wear Protective Gear: Since the plant produces a toxic sap that can irritate the skin, always wear glove and eye protection when handling it. The sap is caustic, so take extra care not to touch it.

Cut the Stem: Use a sharp, sterilized knife or scissors to cut a 4-6 inch section of the stem. Make a clean, straight cut to ensure a healthy new start for the cutting.

Let the Cutting Callous: Place the cutting in a dry, shaded location for several days, allowing the cut end to callous over. This callousing process helps prevent rotting when the cutting is planted.

Prepare the Soil: Use a well-draining cactus or succulent mix. You can also improve drainage by adding sand or perlite to the mix.

Plant the Cutting: Once the cutting has calloused, plant it in a small pot filled with the prepared soil. Insert the cutting a couple of inches deep to ensure stability.

Water Sparingly: After planting, water lightly. Moving forward, allow the soil to

dry out between waterings to avoid root rot. Initially, water very sparingly until the cutting starts to root, which can take a few weeks.

Provide Light: Place the newly planted cutting in a location with bright, indirect light. Avoid direct sunlight, which can stress the cutting during its early growth phase.

Wait for Root Growth: It may take several weeks for the cutting to develop roots. Once rooted, you can begin caring for it like a mature African Milk Tree.

Potting and Repotting African Milk Tree

Potting and repotting an African Milk Tree is essential for maintaining its health and ensuring proper growth. The plant’s tall, upright structure and shallow root system make careful pot selection and occasional repotting crucial for stability and nutrient availability.

Potting the African Milk Tree

• Choose the Right Pot: Select a sturdy pot with drainage holes. The plant’s height and weight can cause it to tip over, so a heavy, wide-bottomed pot (like a terracotta pot) can help provide better stability. Ensure the pot is large enough to accommodate the shallow root system without crowding.
• Soil: Use a well-draining cactus or succulent soil mix. You can also make your own by combining potting soil with sand or perlite for improved drainage. Avoid heavy or water-retentive soil, as this can lead to root rot.
• Potting Process: Fill the pot with the cactus mix, leaving enough room to plant the African Milk Tree. Place the plant in the pot and fill in around the roots, gently patting the soil down to secure it without compacting it too much.
• Watering After Potting: After potting, water lightly to settle the soil, but ensure the soil dries out before the next watering. The African Milk Tree prefers to be kept on the dry side.

Repotting the African Milk Tree

• When to Repot: Repot every 2-3 years or when you notice the plant becoming root-bound or outgrowing its pot. Repot in spring or early summer, when the plant is in its active growing phase.
• Prepare a Larger Pot: Choose a pot that is 1-2 inches larger in diameter than the current one. This will give the roots more space to spread without causing excessive soil moisture retention.
• Remove the Plant: Wear gloves to protect yourself from the plant’s sharp spines and toxic sap. Gently remove the plant from its pot. You may need to tap the sides of the pot or run a knife along the edge to loosen the soil.
• Examine the Roots: Inspect the roots for any signs of rot or damage. If necessary, trim away any unhealthy roots with sterilized scissors.
• Repotting Process: Place the plant in the new pot and fill in around the roots with fresh, well-draining soil. Ensure the plant is centered and stable. Press the soil down gently to support the plant, but avoid compacting it too much, as this can reduce airflow to the roots.
• Watering After Repotting: Water the plant sparingly after repotting. Allow the soil to dry out completely between waterings to avoid stress on the newly repotted plant.

Pests and Diseases

African Milk Trees are generally pest-resistant, but they can occasionally suffer from pests that can damage the plant if left untreated.

Mealybugs and scale insects: Look for small, cotton-like clusters or brown, raised bumps on the stems. Treat infestations with insecticidal soap or neem oil.

Spider mites: If the plant appears dusty or has tiny webs, it may be infested with spider mites. Increase humidity around the plant and treat with neem oil or a mild insecticide.

Disease: The most common disease issue is root rot, caused by overwatering. Ensure proper drainage and allow the soil to dry completely between waterings to prevent this.

African Milk Tree Common Problems

Leggy Growth: If your African Milk Tree starts to grow tall and spindly, it may not be getting enough light. Move it to a brighter location where it can receive more sunlight.

Yellowing Stems: This can be a sign of overwatering. Ensure the soil is completely dry before watering again. Check for root rot and trim off any damaged areas.

Sunburn: If the stems turn brown or red in patches, the plant may be getting too much direct sunlight. Move it to a location with indirect light, especially during the hottest part of the day.

Frequently Asked Questions

Is the African Milk Tree edible?
No, the African Milk Tree is not edible. Its milky sap is toxic and can cause skin irritation or digestive problems if ingested by humans or animals.

What to do when an African Milk Tree gets too tall?
If your African Milk Tree becomes too tall, you can prune it. Use a sharp, sterilized knife to cut the top of the plant, ensuring an even cut. The cuttings can be propagated after they have calloused over. Always wear gloves when pruning due to the toxic sap.

Is the African Milk Tree dog safe?
No, the African Milk Tree is toxic to dogs. If ingested, it can cause vomiting, diarrhea, or other symptoms. Keep the plant out of reach of pets.

How long can an African Milk Tree go without water?
The African Milk Tree is drought-tolerant and can go for several weeks without water. During the growing season, water every 2-3 weeks, and in winter, it can go for 4-6 weeks or more without water, depending on humidity and temperature.

Can I put my African Milk Tree outside?
Yes, you can put the African Milk Tree outside during warmer months if the temperature stays above 40°F (4°C). Place it in a spot with bright, indirect light or morning sun to prevent sunburn.

Do African Milk Trees like full sun?
The African Milk Tree prefers bright, indirect light, though it can tolerate some direct sunlight, especially in the morning or late afternoon. However, it’s best to avoid intense, midday full sun as it can cause sunburn.

What is the pest of the African Milk Tree?
The most common pests are mealybugs, scale insects, and spider mites. Regularly inspect the plant and treat infestations with insecticidal soap or neem oil.

Why is my African Milk Tree falling over?
The plant may be top-heavy due to its rapid vertical growth and shallow root system. Prune it evenly to balance the plant, use a heavier pot for stability, or stake the plant if it’s leaning too much.