Nine times out of ten it is watering, and more often too much than too little. Before you do anything, put a finger two inches into the soil.
Start with the soil, not the leaf
Overwatering and underwatering both produce yellow leaves, and the treatments are opposite, so guessing wrong makes it worse. The soil tells you which one you have. Push a finger in up to the second knuckle:
- Cool and wet, and it has been days since you watered: too much water. Roots that sit in it cannot take up oxygen, and the plant sheds leaves.
- Dry and pulling away from the pot: too little. The plant is dropping older leaves to keep the new ones going.
- Barely damp, and the plant still looks wrong: watering is probably not your problem. Read on.
Then look at where the yellow is
The pattern matters more than the colour. Yellow spreading from the bottom of the plant upward means something different from yellow appearing on the newest growth.
Overwatering or poor drainage
- What it looks like
- Lower leaves yellow first, evenly, and feel soft or limp rather than crisp. Sometimes a sour smell from the soil. Often several leaves at once.
- How to confirm
- Wet soil days after watering. Lift the pot: heavy for its size. Check the drainage hole is not blocked, and that the pot is not sitting in a full saucer.
- What to do
- Stop watering entirely until the top two inches are dry. Empty the saucer. If the soil smells sour or the stem is soft at the base, take the plant out and look at the roots: healthy roots are pale and firm, rotting ones are brown and fall apart. Cut those away and repot in fresh, free-draining soil.
Underwatering
- What it looks like
- Oldest, lowest leaves yellow then go crisp and brown at the edges. The plant may droop at the same time. Soil is dry and may have shrunk from the pot wall.
- How to confirm
- Dry two inches down, and the pot feels light. Water runs straight through and out of the bottom without soaking in, which means the soil has gone hydrophobic.
- What to do
- Water slowly until it stops draining, then again ten minutes later. If it runs straight through, stand the pot in a few inches of water for half an hour so the soil rewets from below. Then set a schedule rather than waiting for droop.
Not enough light
- What it looks like
- Gradual, even yellowing over weeks, usually on the side away from the window. New leaves come in smaller and paler, and the stems stretch with wide gaps between leaves.
- How to confirm
- Watering is fine, and the plant is more than a couple of metres from a window or behind a blind. Leggy growth reaching in one direction is the giveaway.
- What to do
- Move it closer to a window with bright but indirect light. Do it in stages over a week or two: a plant moved abruptly from gloom into strong sun scorches.
Nutrient shortage
- What it looks like
- Yellow between the veins while the veins themselves stay green, often on newer leaves. Common in plants that have been in the same pot for years.
- How to confirm
- Watering and light are right, the plant has not been repotted or fed in over a year, and roots are circling the bottom of the pot.
- What to do
- Feed with a balanced houseplant fertiliser at half the labelled strength during the growing season, and repot into fresh soil if it is pot-bound. Do not feed a plant that is sitting in wet soil: that adds stress rather than removing it.
Pests
- What it looks like
- Yellow stippling or fine pale speckles rather than whole yellow leaves. Sometimes faint webbing where the leaf meets the stem, or sticky residue on the leaf below.
- How to confirm
- Turn a leaf over and look closely at the underside and the leaf joints. Spider mites are barely visible dots; mealybugs look like small tufts of cotton; scale looks like raised brown bumps that do not brush off.
- What to do
- Isolate the plant from your others straight away. Wipe both sides of every leaf, then treat with insecticidal soap or a horticultural oil, repeating weekly for three weeks to catch the ones that hatch after the first pass.
One yellow leaf is usually nothing
Plants shed their oldest leaves. A single lower leaf going yellow on a plant that is otherwise growing well, especially in autumn, is normal ageing rather than a problem. Worry when several leaves yellow at once, when it moves upward through the plant, or when new growth is affected.
Related symptoms
- Brown, crispy leaf tips and edges, which often appears alongside yellowing.
- Drooping or wilting, the other symptom that both over- and underwatering cause.
- All plant symptoms.
General guidance, not a diagnosis of your plant. Which of these five it is depends on what the leaf and soil actually look like, which is what a photo settles.
Not sure which one it is?
This page narrows it down. A photo settles it: Bloom names the species, scores its health out of 100, and pairs each problem it finds with the treatment for it.
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