Yellowing leaves on geraniums  can be caused by several problems, including overwatering, underwatering, nutrient deficiencies (especially nitrogen), insect infestations and disease. It’s important to identify the cause of the problem before deciding whether or not to cut off yellow leaves because they may still be alive and could continue to draw nutrients away from healthy parts of the plant.

Watering Problems

Overwatering is one of the most common reasons that geraniums will turn yellow, especially in the lower leaves. Since geraniums are somewhat drought-tolerant, you should only water them when the top 1-2 inches of soil feels dry to the touch. Overwatering can lead to root rot and other problems. You should also check the soil ph regularly and make adjustments to prevent overly acidic conditions.

Unveiling the Mystery: Why Are My Geranium Leaves Turning Yellow

Geraniums are fairly tolerant of most common nutrient deficiencies, but it’s best to use a soil test kit to find out what your garden needs. You can add a diluted fertilizer to the soil to help remedy any deficiency. Chelated zinc is the easiest for geraniums to absorb, so you should use a fertilizer that contains this mineral. If the plants are suffering from a magnesium deficiency, you can try soaking them in Epsom salts. Potassium can be added with kelp meal, aged horse, cow, or chicken manure, coffee grounds, and homemade compost.

If the yellowing is due to disease, you should always remove dead or dying foliage. Pests and disease can harbour on these discarded leaves and may spread to other areas of the garden. If the disease is a fungal infection, you should spray the infected area with fungicide. Bacterial infections such as blight or southern bacterial wilt, can also discolor the foliage and cause wilting and thinning of leaves.