Nutrient deficiency is often the most likely reason for the yellowing of many older leaves. It indicates insufficient nitrogen or magnesium. Apply a high-nitrogen fertilizer, such as 2-1-1.

If your gardenia leaves are yellowing, ... copper, magnesium, nitrogen, ... these minerals will be unusable for the plant and it will suffer from deficiency — which causes yellow leaves.

Regarding nitrogen deficiency, it is the easiest of all deficiencies to diagnose. Like magnesium, nitrogen is highly mobile and when you see a branch with leaves that are pale green to yellow ...

Acidic soil: Gardenias prefer acidic soil, which helps them gain better access to nutrients.If the pH of the soil is alkaline, yellow leaves will develop. Keep soil between a pH of 5.0 and 6.0 ...

Frequently gardenia plants will become yellow (chlorotic) due to iron deficiency caused by alkaline soils. There are a couple of remedies. Chelated iron, applied to the soil, often compensates for ...

M.B.: The sweet-smelling gardenia craves an acid plant food. It sounds as if your gardenia has a magnesium deficiency, which is very common in gardenias and easy to fix. You can dissolve one ...

Q: My azaleas have turned somewhat yellow. The plants otherwise look OK. What could do this? Earl, B.A.