Sunburn on opuntia
What's Happening
Cactus sunburn occurs when plants acclimated to low light are suddenly exposed to intense direct sunlight. The waxy cuticle and epidermal cells cannot dissipate excess solar energy, causing cellular breakdown that appears as bleached, scarred, or corky tissue. Unlike etiolation (gradual stretching), sunburn is acute damage that cannot be reversed—affected tissue forms permanent corky scars. The damage typically appears on upper/southern-facing surfaces and can be confused with rot, but sunburn tissue remains firm while rot is soft.
How to Fix It
- 1
Gradual acclimation: Move plants to full sun over 7-14 days (start with 1-2 hours morning sun)
- 2
Immediate shade: Relocate sunburned plant to bright indirect light only
- 3
Assess damage: Sunburn = firm, discolored tissue; Rot = soft, mushy tissue with odor
- 4
Prune if needed: Remove severely damaged pads only if affecting plant stability
- 5
Prevent further damage: Use shade cloth (30-50%) during peak summer hours
- 6
Monitor recovery: New growth will emerge healthy if light conditions corrected
What You'll Need
How to Prevent It
Never move indoor cacti directly to full outdoor sun. Acclimate gradually over 2 weeks, increasing sun exposure by 1-2 hours daily. Use UV-filtering window film for south-facing windows. Maintain consistent light levels—sudden increases cause more damage than gradual exposure.