What is Geranium Edema?
Edema of geraniums is a physiological disorder rather than a disease. It is not so much a disease because it is the result of adverse environmental issues. It also doesn’t spread from plant to plant. It can afflict other plant varieties though, such as cabbage plants and their relatives, dracaena, camellia, eucalyptus, and hibiscus to name a few. This disorder seems to be most prevalent in ivy geraniums with large root systems compared to shoot size.
Symptoms of Geraniums with Edema
Geranium edema symptoms are first viewed atop the leaf as small yellow spots between the leaf veins. On the underside of the leaf, small watery pustules can be seen directly under the surface’s yellow areas. Both the yellow spots and blisters generally occur on older leaf margins first. As the disorder progresses, the blisters enlarge, turn brown and become scab-like. The whole leaf may yellow and drop from the plant. The resulting defoliation is similar to that of bacterial blight.
Edema of Geraniums Causal Factors
Edema most likely occurs when air temperatures are lower than those of the soil combined with both soil moisture and relatively high humidity. When plants lose water vapor slowly but absorb water rapidly, the epidermal cells rupture causing them to enlarge and protrude. The protuberances kill the cell and cause it to discolor. The amount of light and lack of nutrition combined with high soil moisture are all contributing factors to edema of geraniums.
How to Stop Geranium Edema
Avoid overwatering, especially on overcast or rainy days. Use a soilless potting medium that is well-draining, and do not use saucers on hanging baskets. Keep the humidity low by increasing the temperature if need be. Geraniums tend to naturally lower the pH of their growing medium. Check the levels at regular intervals. The pH should be 5.5 for ivy geraniums (the most susceptible to geranium edema). Soil temperatures should be around 65 F. (18 C.).
