Why are my plant leaves turning yellow?

Yellow leaves are a symptom, not a diagnosis. Which leaves yellow, and in what pattern, points at the cause: lower leaves first suggests one thing, yellow between the veins another, and uniform yellowing across the whole plant another again.

What you'll need

• Finger or moisture meter (optional)

Step by step

1. Check the soil moisture 5cm down before anything else.Push a finger in. Soggy means overwatering; bone dry means underwatering. Both produce yellow limp leaves, which is why people water a drowning plant.
2. If it is waterlogged, stop watering and improve drainage.Check the pot has drainage holes and is not standing in a saucer of water. Roots suffocate in saturated soil and cannot take up water, which is why the plant looks thirsty.
3. Yellowing lower leaves first usually means nitrogen shortage.The plant is moving nitrogen from old leaves to new growth. A balanced feed corrects it, and it is common in pots where nutrients have leached out.
4. Yellow between green veins means a micronutrient problem.Usually iron or magnesium, often because the soil is too alkaline for the plant to absorb what is there. Ericaceous feed helps acid-lovers.
5. Uniform yellowing on a houseplant often means too little light.Pale, leggy growth alongside yellowing confirms it. Move it closer to a window gradually rather than suddenly.
6. Check the undersides of leaves for pests.Aphids, red spider mite and whitefly cause stippled yellowing. Look closely — spider mite is barely visible and leaves fine webbing.
7. Consider recent changes.Repotting, moving, a cold draught or a radiator underneath all cause yellowing a week or two later. Plants react on a delay.
8. Accept some yellowing as normal.Older lower leaves yellow and drop naturally throughout a plant's life. A few is not a problem; a spreading pattern is.

Tips

• More houseplants die from overwatering than from anything else. Watering on a schedule rather than by checking is the usual reason.
• Yellow leaves rarely turn green again. Judge whether the treatment is working by new growth, not by the leaves already affected.
• Tap water in hard water areas raises soil pH over time, which causes yellowing in acid-loving plants specifically. Rainwater fixes it.

Common mistakes

• Watering more because the leaves look limp — Overwatered plants look thirsty because damaged roots cannot absorb water. Adding more makes it worse.
• Feeding a stressed or waterlogged plant — Fertiliser on damaged roots burns them further. Fix the water problem first, then feed once it recovers.
• Removing every yellow leaf immediately — The plant is still reclaiming nutrients from them. Remove them once they are fully yellow or brown, not at the first sign.

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