When a geranium turning yellow, it can be a sign of an infection or poor plant care. If it’s the former, prompt diagnosis and treatment should bring back the leaves to green. If the problem is a fungal disease, it can be much more difficult to get rid of.
Waterlogged soil prevents the geranium’s roots from getting the nutrients they need and causes yellowing leaves, wilting, and stunted growth. Make sure the potting mix is well-draining and use compost, sand, and gravel to amend it if necessary. Water the geranium only when the top inch of soil feels dry.
Like many other plants, geraniums need ample sunlight to thrive. Insufficient light can cause the leaves to turn yellow, especially on older leaves near the bottom of the plant. If possible, move the geranium to a sunnier location or prune nearby trees or shrubs to let it receive more direct sunlight.
A number of nutrient deficiencies can turn a geranium’s leaves yellow, depending on the type of deficiency and the symptoms. Zinc deficiency causes new geranium leaves to turn yellow in between the veins, while magnesium and nitrogen deficiencies create yellow spots at the leaf edges. Rebalancing the fertilizer schedule and removing any contaminated soil should help restore the leaves to their proper color.