Why Your Moon Cactus Lost Its Red Top & What to Do Next

Kevin had kept a grafted "moon cactus" (a bright red Gymnocalycium atop a green Hylocereus rootstock) for 12 years. The red top eventually dried up and turned brown, while the rootstock sprouted long arms with aerial roots. He hoped to propagate a new red top from the arms.

Greg explained that the red ball was a completely separate, chlorophyll-deficient cactus grafted onto the rootstock. Its red color comes from irradiation that alters chlorophyll. Once the graft dies, it cannot regenerate from the rootstock. The arms are purely the rootstock (Hylocereus) and will never produce a red top.

The only way to get the red ball back is to purchase a new grafted plant. Greg provided a link explaining the grafting process.

Understanding Grafted Cacti

• The colorful top is a mutant Gymnocalycium that cannot survive on its own.
• Rootstock provides water and nutrients; the scion provides the color.
• If the scion dies, the rootstock lives on but reverts to its natural green form.