How to Grow and Care for Sea Urchin Cactus

The Sea Urchin Cactus is a popular plant valued for its low-maintenance nature and impressive flowering capabilities. Its globular, ribbed body grows in a clumping habit by freely producing offsets, also known as pups, from its base. Over time, these pups can form a large, mounded cluster, adding to its distinctive appearance.

Sea Urchin Cactus Identification

The plant commonly called the Sea Urchin Cactus is scientifically known as Echinopsis multiplex. It is closely related to and sometimes considered a variant of Echinopsis oxygona, leading to some overlap in common names like Easter Lily Cactus. This cactus is characterized by its globular to short-cylindrical stem, which can grow between 15 to 30 cm in height.

The green body, which may become grayish-green with age, features 12 to 15 pronounced, straight ribs. These ribs are lined with areoles, small woolly pads from which the spines emerge. The spines themselves can vary in color from yellowish-brown to blackish and are stout and spreading. Distinguishing it from similar cacti comes down to its specific combination of rib count and spine characteristics.

Comprehensive Care Guide

Light

This plant thrives with plenty of sunlight, receiving at least six to eight hours of direct sun each day. When grown indoors, placing it near a south-facing window is the best option for robust development and potential blooming. If moving a plant from a lower-light indoor environment to a brighter outdoor spot, acclimate it gradually. A sudden shift into intense, direct sun can cause sunburn on the cactus’s stem.

Soil

The soil for a Sea Urchin Cactus must provide excellent drainage to prevent moisture-related issues. A commercial potting mix formulated for cacti and succulents is a suitable choice. To enhance drainage, you can amend the mix by incorporating materials like perlite or coarse sand, ensuring water flows freely through the pot.

Water

During the active growing season of spring and summer, the plant benefits from thorough but infrequent watering. Water approximately every two to three weeks, allowing the soil to dry out completely between sessions. In the winter, the plant enters a dormant period, and its water needs decrease significantly. During this time, watering should be reduced to a minimum while the plant is resting.

Temperature and Humidity

The Sea Urchin Cactus prefers warm conditions that mirror its native South American habitat. The daytime temperature range for active growth is between 18°C and 35°C (65°F and 95°F). While it can tolerate cooler temperatures, it is sensitive to frost, which can cause permanent damage. In colder climates, it is best to bring the plant inside before the first frost. This cactus adapts well to household humidity levels.

Fertilizer

This cactus has modest nutritional needs, as it is adapted to grow in nutrient-poor soils. During the growing season from spring through early fall, provide a balanced fertilizer formulated for cacti and succulents. Feeding should occur about once every one to two months. Dilute the fertilizer to half-strength to avoid over-fertilizing, which can harm the plant.

How to Encourage Blooms

Achieving the large, showy flowers of the Sea Urchin Cactus hinges on providing a period of winter dormancy. These cacti need a distinct rest to set buds for the following spring and summer blooming season. This involves significantly reducing watering from October through March and stopping fertilizer applications completely. The plant should be moved to a cool, bright location for the duration of this rest.

An unheated room or a conservatory where nighttime temperatures can drop is suitable, as temperatures around 4-7°C (39-45°F) are effective. This cool, dry period mimics the seasonal changes of its natural habitat, signaling the plant to prepare for its flowering cycle. When spring arrives, gradually resume normal watering, which triggers the emergence of fuzzy flower buds from the areoles. The flowers are large, funnel-shaped, pink or lavender, opening in the evening and lasting for about a day.

Propagating Sea Urchin Cactus

Multiplying a Sea Urchin Cactus is easily accomplished using the offsets, or pups, it produces. The best time for this is during the spring or summer growing season. Select a healthy pup that is at least an inch or two in diameter. Gently twist and pull the offset away from the base of the mother plant, or use a clean, sharp knife to make a cut as close to the parent as possible.

Once the offset is removed, allow the cut surface to dry and form a callus by placing it in a dry, shaded area for several days to a week. This healing process prevents rot when the new plant is potted. After the callus has formed, plant the offset’s base into a pot with a well-draining cactus mix, just deep enough to keep it upright. Water sparingly until new growth appears, which indicates that roots have formed.

Troubleshooting Common Problems

Root rot is a common issue caused by overwatering. A rotting plant may become soft and squishy or develop dark, mushy patches at its base. To address this, unpot the plant, cut away any affected root or stem tissue, and allow it to dry before repotting in fresh, dry soil.

Insufficient light leads to a condition called etiolation, where the cactus stretches toward a light source, becoming pale and misshapen. This damage is permanent, so prevention by providing adequate sunlight is the only solution.

Pests can also present challenges, with mealybugs and spider mites being common. Mealybugs appear as small, white, cottony masses on the plant, often hiding between the ribs or near the base. Spider mites are tiny and difficult to see, but their presence is often revealed by fine webbing or a silvery, scarred appearance on the plant’s surface. For small infestations, dabbing individual pests with a cotton swab dipped in isopropyl alcohol is effective.