potted geranium–leaves are turning yellow and red
What is causing my geranium leaves to loose their green coloring?
Red geranium leaves signal the plant is stressed in some way. This may be because the plant is receiving too much water or too much sunshine, or has been planted outdoors too early or in mineral-deficient soil.
Fast-growing geraniums have small root systems that are vulnerable to deficiencies of phosphorus and trace minerals. Treat slow-growing, red-leaved plants with a high-phosphorus liquid fertilizer every two weeks during the growing season. For example, mix 1 tablespoon of water-soluble, 5-15-15 fertilizer with 1 gallon water to offset deficiencies and encourage blooms.