Why are the leaves on my geraniums turning yellow?
Yellowing leaves of geraniums may indicate nitrogen deficiency or fungal disease. Before applying fertilizers or pesticides, use a soil pH meter to ensure that the soil acidity is right for the geranium which is between 6.0 to 6.5.
If the soil is too acidic, you may apply lime but if it’s too alkaline, you may apply sulfur.