Oedema can be a problem on plants during periods of cool and cloudy weather, reports Univ. of Md. Extension personnel. Symptoms appear as corky, tan spots on foliage. Geraniums, begonias, kalanchoes and begonias are usually the plants most often affected, but any broadleaved plant is susceptible. The cause is plants take in water faster than they can use it resulting in some plant cells to rupture.
Univ. of Mass. Extension floriculture specialist Tina Smith said do not over water plants, and keep the growing medium on the “dry side” during extended periods of low light and cool temperatures. Reducing humidity, by venting the greenhouse, also helps to control the disorder.