Geraniums are reliable, sturdy plants that require little maintenance to keep them blooming throughout the growing season. While growing geraniums offers many advantages and few disadvantages, there are a few problems that may befall geraniums. Fortunately, geraniums usually remain healthy all season.
Geraniums are cold tender and won’t survive past the first frost in autumn. Saving geraniums over the winter is sometimes possible if the plants can be stored in a cool, non-freezing place. Most gardeners prefer to start with new geranium plants every spring, as overwintering isn’t always successful. Only the healthiest geraniums are overwintered, as any pests or disease will be carried over to the next growing season.
Botrytis is a fungal disease that is often harmful to geraniums, especially during cool, damp weather. The fungus appears as a brown, moldy growth on the flowers first, before spreading rapidly from flower to petal, then from plant to plant. Removing blooms as soon as they begin to wilt helps to halt the spread of botrytis. Full sunlight, plenty of air circulation between plants and fairly dry soil helps to prevent botrytis. Although geranium is sometimes affected by other fungal diseases, botrytis is the most common.
Xanthomonas is a bacterial disease that attacks the vascular system of geraniums. The leaves of affected plants turn yellow or brown before the plant eventually dies. The disease is easily transmitted to other geranium plants through the soil or by gardeners touching other plants with unwashed hands. Affected plants are disposed of in the garbage and are never placed on a compost pile. New geraniums are not planted in the spot for a season, as the soil remains in the soil for three months.
Geraniums are relatively pest-free but are sometimes plagued by insects. A spray of insecticidal soap is usually enough to control aphids, mites and whiteflies that dine on the juice of the leaves. Caterpillars such as leaf rollers, cabbage loopers and cankerworms are controlled with a biological control spray such as Bacillus thuringiensis. Slugs are picked off by hand or controlled by slug baits or other commercial treatments.