The Sea Urchin Cactus, known for its distinctive spherical, spiny appearance, is a popular houseplant. This succulent, a member of the Echinopsis genus from South America, is often identified as Echinopsis calochlora or Echinopsis eyriesii. Its unique aesthetic, reminiscent of a sea urchin, makes it a favored choice for many plant enthusiasts.
Identifying Your Sea Urchin Cactus
The Sea Urchin Cactus typically exhibits a globular or flattened spherical shape, sometimes becoming cylindrical with age. Its dark green body features 9 to 18 prominent, sharp-edged ribs running vertically along the stem. Circular areoles, up to 1 cm apart and often filled with white or tawny wool, are found along these ribs.
From these areoles emerge short, stiff spines that radiate outwards; for example, Echinopsis calochlora has dark gray, needle-like spines, including a single central spine and eight to nine radial spines. The plant also produces striking, funnel-shaped flowers, often 8 to 10 inches long, which can be white, pink, yellow, or orange and may bloom at night. These flowers emerge from the apex of the stem.
Essential Care Requirements
Light
Sea Urchin Cacti thrive in bright, direct sunlight, needing at least 6 to 8 hours daily for strong growth and abundant blooms. Indoors, a south-facing window provides optimal light. Acclimate the cactus to intense sunlight gradually, especially when moving it outdoors, to prevent sunburn.
Watering
Proper watering is important for Sea Urchin Cactus health, as it is susceptible to overwatering and root rot. Use a “soak and dry” method, allowing the soil to dry completely between waterings. During the active growing season, when daytime temperatures consistently exceed 21°C (70°F), water regularly.
As fall approaches and temperatures drop below 21°C (70°F), the cactus enters a semi-dormant period, and watering should be cut back significantly, to about once a month or less. Some growers suspend watering completely during winter dormancy. If buds are forming, prevent the pot from becoming bone dry.
Soil and Potting
A well-draining, gritty cactus or succulent mix is important for the Sea Urchin Cactus to prevent waterlogged roots. An appropriate mix can be created by combining 40% perlite or small crushed rock, 20% sand, and 40% regular potting soil. Pots with drainage holes are also important for drainage. While Echinopsis have shallow root systems, shorter “azalea pots” are suitable.
Temperature and Humidity
Sea Urchin Cacti prefer warm temperatures during their active growth phase, between 18°C to 35°C (65°F to 95°F). While they tolerate some cooler temperatures, they are sensitive to frost and very low temperatures, requiring protection from hard freezes. During winter dormancy, a cooler period is beneficial and can promote better blooming the following year. These cacti are well-suited to low humidity environments.
Fertilizing
Fertilize the Sea Urchin Cactus during its growing season, typically spring and summer. A balanced liquid fertilizer, or one formulated for cacti with higher phosphorus (e.g., 15-30-15), can promote growth and blooming. Dilute the fertilizer to half or quarter strength to prevent root burn. Suspend fertilization during the dormant winter period.
Propagation and Repotting
Propagation
Sea Urchin Cacti can be easily propagated from offsets, also known as pups, which cluster around the base of the mother plant. Remove these offsets for propagation during the active growing season, when daytime temperatures are consistently above 22°C (70°F). Gently twist the pup off the parent plant or use a clean knife, ensuring it is at least 1 inch in diameter.
After removal, allow the cut surface to dry and form a callus for a few days to a few weeks to prevent rot. Once callused, plant the pup in a fast-draining rooting mixture, barely moistening the soil to encourage root growth. Keep the newly planted pup in a shaded area initially, gradually moving it to a brighter spot as it establishes roots.
Repotting
Repotting your Sea Urchin Cactus is necessary when it becomes root-bound or every few years to refresh the soil. The best time for repotting is during the warm growing season. Before repotting, ensure the soil is dry, then carefully remove the plant from its current pot.
Gently remove old soil from the roots and trim any rotted or dead sections. When selecting a new pot, choose one that is slightly larger than the previous one. Place the plant in the new pot, spreading its roots, and backfill with a fresh, well-draining cactus potting mix. After repotting, avoid watering for about a week to allow any damaged roots to heal, then resume light watering.
Troubleshooting Common Issues
Overwatering is a common problem for Sea Urchin Cacti, often leading to root rot. Signs of rot include softening or discoloration of the cactus body. Conversely, underwatering can cause the cactus to shrivel. Adjusting watering frequency and ensuring proper drainage can resolve these issues.
A lack of growth or flowering may indicate insufficient light or nutrients. Moving the plant to a brighter location or applying a diluted cactus fertilizer during the growing season can help stimulate growth and encourage blooms. Common pests include mealybugs and spider mites, which weaken the plant by feeding on its sap. Mealybugs appear as fuzzy white insects, while spider mites may cause fine webbing and small brown dots on the plant. Addressing these pests can involve wiping them off with rubbing alcohol or using horticultural oil.