Gymnocalycium

Gymnocalycium is a popular genus of small, rounded cacti native to the dry regions of Argentina and Paraguay. Unlike natural green or brown forms that contain chlorophyll, colorful decorative varieties (such as Gymnocalycium mihanovichii) lack chlorophyll and cannot feed themselves through the roots. They must be grafted onto a green cactus (usually Hylocereus), which supplies them with nutrients. Thus, the name “Gymnocalycium” in trade usually refers to two plants: the green rootstock and the colorful graft. For successful cultivation, favorable conditions must be created for both parts.

Placement

Gymnocalycium requires bright but indirect light. Direct sunlight can scorch the colorful top. East- or west-facing windows are ideal. On the south side, light shading is recommended. Northern windows provide insufficient light.

Watering

Water moderately. In spring and summer, water about once every 7–10 days, allowing the soil to dry completely. In winter, during dormancy, reduce watering to about once a month. Overwatering causes root rot, but the plant should not be left shriveled either. It is safer to underwater than overwater. Always use soft, lime-free water.

Fertilizing

Fertilize only during the active growing and flowering season, from April to September. Use cactus and succulent fertilizers low in nitrogen but rich in potassium and phosphorus. Apply about once every 3–4 weeks. Do not fertilize in winter.

Repotting

Young plants are repotted every spring into a slightly larger pot. Mature plants can be repotted every 2–3 years. The soil must be loose, well-draining, and airy. A mix of turf soil, sand, and gravel works well. Always provide a thick drainage layer at the bottom of the pot.

Temperature

In summer, Gymnocalycium thrives at +20…+28 °C and can be placed outdoors if protected from rain. In winter, it requires cooler conditions around +12…+15 °C. Below +10 °C, the green rootstock may die.

Pruning

The colorful top does not require pruning. However, side shoots from the green base should be removed regularly as they draw nutrients away from the graft. Apply crushed charcoal to the cut areas.

Conclusion

Gymnocalycium is an ideal choice for those seeking a hardy yet decorative plant. It requires bright but gentle light, rare watering, moderate feeding during the growing season, repotting every few years, and cool winter conditions. With proper care, it will delight you for many years.