How to Grow and Care for a Ruby Ball Cactus
Successfully grow a vibrant Ruby Ball Cactus by understanding its unique biology. This guide explains how its grafted nature dictates its care and long-term health.
The Ruby Ball Cactus, scientifically Gymnocalycium mihanovichii, is a popular houseplant known for its vibrant, spherical top. These cacti are a common sight in garden centers, with colors ranging from bright red and pink to orange and yellow. Their small size and unique look make them a frequent choice for indoor spaces, dish gardens, and succulent collections.
Understanding the Grafted Nature
The most distinct feature of the Ruby Ball Cactus is that it is two different cacti joined by grafting. The colorful, globe-shaped top is the scion, a mutant Gymnocalycium mihanovichii. This scion has a genetic mutation that prevents it from producing chlorophyll, the pigment for photosynthesis. Without chlorophyll, the top cactus cannot create its own food and would not survive on its own.
To solve this, the colorful scion is grafted onto a different cactus known as the rootstock, often a hardy species like Hylocereus. The green rootstock performs all the photosynthesis, providing nutrients to support both itself and the scion. This symbiotic relationship allows the non-viable colored cactus to grow.
Ruby Ball Cactus Care Guide
Light
The colorful scion is sensitive and can be scorched by intense, direct sunlight, while the green rootstock needs bright light. The ideal placement is a location that receives bright, indirect sunlight for most of the day. An east-facing window providing gentle morning sun is a suitable spot to energize the rootstock without harming the top.
Water
Overwatering is a common issue for these cacti, as they are susceptible to root rot in damp soil. Use a “soak and dry” method, allowing the soil to dry out completely between waterings. When watering, do so thoroughly until water runs from the drainage holes, and discard any excess from the saucer. During the dormant winter months, reduce watering significantly.
Soil
Proper soil is important for drainage. A well-draining cactus or succulent potting mix is recommended. You can buy a commercial mix or create your own by combining potting soil with inorganic materials like perlite or coarse sand. The goal is a medium that does not retain excessive moisture, which helps prevent root rot.
Temperature and Humidity
Ruby Ball Cacti thrive in average room temperatures, between 68°F and 82°F (20°C to 28°C), and do not have demanding requirements. They prefer the low humidity found in most homes, so it is not necessary to supplement it. Overly moist air can be detrimental to the plant.
Fertilizer
During the spring and summer growing season, feed the cactus monthly with a balanced fertilizer for cacti and succulents, diluted to half strength. Suspend feeding during the fall and winter when the plant’s growth slows. Always apply fertilizer to moist soil to avoid burning the roots.
Repotting and Propagating a Ruby Ball Cactus
Repot a Ruby Ball Cactus every two to three years, or when it outgrows its container. The best time is spring as the plant enters its active growth phase. Choose a new pot that is slightly larger than the old one and has excellent drainage. Handle the plant gently, avoiding pressure on the fragile graft union.
Propagating a Ruby Ball Cactus is challenging due to its grafted nature. The colorful scion cannot survive on its own, but it may produce small offsets, or “pups.” These can be carefully removed and grafted onto a new rootstock cactus. If the top scion perishes, the green rootstock can be cut and rooted to grow as its own plant.
Common Ruby Ball Cactus Problems
A frequent issue is rot, which appears as soft, mushy spots at the base of the rootstock or at the graft joint. This problem is almost always caused by overwatering. If rot is discovered, it can be difficult to reverse, especially if it has advanced significantly.
The eventual failure of the graft is a common occurrence. The scion and rootstock grow at different rates, which puts strain on the union and can cause them to separate. Because of this, these plants often have a shorter lifespan of just a few years. A shriveling scion on a healthy rootstock often signals a failing graft, which is a natural part of this plant’s life.
The green rootstock may sprout its own arms or branches. While this indicates the rootstock is healthy, this new growth diverts energy from the colorful scion. To ensure the scion receives the support it needs, carefully prune these side shoots with a clean, sharp knife.
Pests are not a major problem, but Ruby Ball Cacti can be affected by mealybugs or spider mites. These pests often cluster around the cactus ribs or at the graft union. Treat an infestation by dabbing the pests with a cotton swab dipped in rubbing alcohol or by using horticultural oil.