Edema refers to the swollen, blister-like protrusions that can appear on the leaves and stems of some succulents and cacti. It is caused by the abnormal buildup of fluid in the plant’s tissues.
This condition is brought on by:
- Overwatering – Excess moisture is taken up by the cells, causing them to enlarge and burst through the outer skin.
- Low temperatures – Cooler weather slows the plant’s fluid absorption, leading to excess water in cells.
- High humidity – Moist air prevents proper evaporation through the pores (stomata) on leaves.
- Sun exposure after watering – Rapid heating after watering drives water accumulation in cells.
While unsightly, mild cases of edema won’t seriously harm the plant. But overwatering and improper conditions need to be corrected to avoid secondary infections and rotting. Edema serves as a visual indicator of abnormal, excess-wetness stress.