Most commercial potting soil mixes can be used as a germinating media. Avoid coarse medias with large particles. The International Geranium Society publishes a bulletin containing detailed information on specific geranium topics. International Geranium Society, P.O. Box 927934, Pasadena, CA 91109-2734. Diseases Plant diseases are one of the key limiting factors in the production of geraniums by commercial growers and home gardeners.
Strict sanitation is basic to the successful culture of disease-free geraniums.
If necessary, fungicides can be used to augment sanitary measures, but they cannot replace them. Commercial growers should familiarize themselves with common diseases and be prepared to act promptly if serious disease problems arise. Rotating the geranium bed, so that at least three years elapse before the site is again planted to geraniums, is probably the most practical preventive disease control measure available to the home gardener. This is a decision gardeners have to make for themselves. Primarily a greenhouse problem where relative humidity is high and air circulation poor.