As the weather cools, a common problem in home produce gardens is yellowing of citrus leaves. This is often caused by the cooler weather making nutrients harder for the plant to access. Here we address three of the most common causes of leaf yellowing in citrus grown in North-East Melbourne and how the can be treated.

Iron Deficiency
Appearance: Yellowing of new leaves, sometimes leaving green around leaf veins
Possible causes: Iron can become ‘locked up’ in the soil and not available to the plant. Two common causes of this are cool soil temperatures in winter and high soil pH.
Treatment: Test the pH of your soil to make sure it’s appropriate for growing citrus. Citrus trees prefer a soil with a pH of 5.5 to 6.5. Inexpensive soil pH test kits are available from nurseries and hardware stores. If the pH is too high, it can be adjusted using a soil acidifier or Iron Sulfate. If the soil pH is at an appropriate level, iron can be added using iron chelate solution.

Magnesium Deficiency
Appearance: Yellow blotches appear on leaves, and join together leaving a green triangle or ‘dagger’ at the base of the leaf.
Possible causes: Can be caused by falling availability of soil magnesium due to cold weather or depletion by the plant using up available magnesium.
Treatment: This is most easily corrected by applying epsom salts. A foliar spray of Magnesium nitrate can also be used.

Nitrogen Deficiency
Appearance: Leaves yellow more or less evenly, starting with older leaves. Sometimes the leaf veins yellow first.
Possible Causes: Citrus can be very ‘hungry’ plants, nitrogen deficiency is often caused by them using up the nitrogen in the soil. As with the other nutrients, bioavailability can be lower in winter and early spring due to low soil temperatures.
Treatment: Application of a high nitrogen fertiliser such as pelletised poultry manure.