Yellowing Base on Small Round Cactus: Rot or Stress?

A baseball-sized round cactus with yellowing at soil line and patchy underside: if firm, likely cultural stress; if soft, fatal rot.

Diagnosis by Touch

• Firm, hard yellowing: Corking (natural aging), sunburn, or mineral deposit
• Soft, mushy, yields to pin: Rot—progresses upward
• Spines pull out easily: Advanced rot

If Firm (Cultural)

• Reduce watering: only when bone dry
• Bright light, no direct sun (acclimate slowly)
• Check for pests (mealybugs at base)
• Repot in gritty mix if soil organic-heavy

If Soft (Rot)

1. Unpot; wash roots
2. Cut away all brown/black tissue
3. Dust with sulfur/cinnamon
4. Callus 1-2 weeks
5. Reroot in dry gritty mix
6. Discard old soil; sterilize pot

Prevention

• Terra cotta pot with drainage
• 50% pumice/perlite in mix
• Water by weight (pot light = dry)
• Winter: monthly water max

Small cacti rot fast. Act immediately if soft. If firm, adjust culture and monitor.