Yellow leaves
A common sign of a problem rather than a disease in itself, where leaves lose their green colour because of watering, light, nutrient or root problems.
Also known as: Yellowing leaves, Leaf yellowing
Symptoms and identification
Leaves turn pale green to yellow, either over the whole leaf, along the edges or between the veins. Older leaves yellowing first usually points to overwatering or a lack of nitrogen. Yellowing on new leaves often points to an iron or other trace-element shortage.
Causes
Overwatering and poor drainage are the most frequent causes, followed by underwatering, lack of nutrients, not enough light, root damage, pests such as spider mites and aphids, and natural ageing of the lowest leaves.
Organic treatment
Check the soil moisture, drainage and roots first, then look under the leaves for pests. Correct the watering, feed with a balanced organic fertiliser if the plant is hungry, and remove leaves that are fully yellow.
Prevention
Water only when the top of the soil is dry, use pots with drainage holes and a free-draining mix, feed regularly during the growing season, and give plants the right amount of light.
Chemical treatment (use with care)
Use a balanced liquid fertiliser or a chelated trace-element feed only once you know the cause is a nutrient shortage, as the label directs.