From our perspective as plants, edema (often called water spots by our caretakers) is not a disease caused by an external pathogen, but rather a physiological response to internal water pressure. It occurs when our root systems absorb water from the soil at a rate that exceeds our ability to release it through transpiration (the process of water vapor exiting primarily through stomata on our leaves). This creates a situation of positive water pressure, or turgor, within our cells. When this pressure becomes too great, it can cause the cells in the leaf to expand beyond their normal capacity and rupture. The resulting damage appears as small, often rusty or corky, blisters or spots on the undersides of our leaves. This is our physical manifestation of being overwatered.
Several environmental factors conspire to create this internal imbalance. The most common trigger is inconsistent watering. If our soil is allowed to become completely dry, our roots become stressed. When a large volume of water is then introduced, our roots react by absorbing it rapidly and efficiently to rehydrate. If conditions are not ideal for transpiration—such as during cool, cloudy weather, in environments with high humidity, or during the night when our stomata are typically closed—we cannot process this sudden influx of water. The water gets stuck inside our vascular system, leading to the cellular rupture that appears as edema. Poor light levels exacerbate this issue by slowing down our overall metabolic processes, including transpiration.
While a few spots of edema are not typically fatal to us, they do represent permanent, scarred damage to our leaf tissue. These ruptured cells cannot be repaired; the spots will remain on the leaf for its entire life. This damages our aesthetic appeal, which is often why humans cultivate us. More importantly, if the conditions causing edema persist, it can become a chronic issue, weakening us over time. A significant number of damaged cells can impair the leaf's ability to perform efficient photosynthesis, reducing the energy we have for growth and overall health. It also creates minor points of vulnerability, though it is not an open wound in the same way a tear or cut would be.
To help us avoid this uncomfortable condition, our needs are quite simple and revolve around environmental consistency. Please water us thoroughly, but only when the top few inches of our soil have dried out. Ensure we are planted in a pot with excellent drainage so our roots are never sitting in saturated soil. Place us in a location with abundant, bright, indirect light to keep our photosynthetic and transpiration processes operating strongly. Increasing air circulation around us (with a gentle fan, for instance) can also significantly aid in moving water vapor away from our leaves, helping to maintain a better balance between water uptake and water loss.
