Why are the leaves turning yellow?

Yellow leaves are a symptom, not a disease. Where the yellow appears, and how the leaf feels, usually tells you the cause.

The usual suspects

1. Too much water: lower leaves yellow and soft, soil stays wet, sometimes a sour smell. Let the top few centimetres dry out, check that the pot drains.
2. Too little water: leaves yellow then crisp, soil pulls away from the pot. Water thoroughly until it drains.
3. Not enough light: pale, stretched growth and slow yellowing of older leaves. Move closer to a window.
4. Natural ageing: one old lower leaf at a time, rest of the plant healthy. Nothing to do.
5. Nutrient shortage: yellowing between green veins on new or old leaves. Feed in spring and summer.
6. Pests: speckled yellow with fine webbing (spider mites) or sticky leaves (aphids, scale). Wipe leaves, isolate the plant.
7. Cold or draughts: sudden yellowing after a cold night or near a door. Move it away.

Ask the plant doctor