Why are my plant's leaves turning yellow?

A yellow leaf is an extremely common symptom, and one that can hold many meanings. It's also the least specific signal a plant can give you which can make identification of the problem tricky. A yellow leaf can mean too much water or not enough, too much sun or too little, or simply that a leaf has come to the end of its life.

The good news is that the causes look quite different once you know what to compare. Below are the six reasons a houseplant's leaves turn yellow, what each one actually looks like, and what to do next.

First, check the soil

Before you diagnose anything, push a finger into the soil up to the second knuckle to gauge the current conditions.

If the soil feels damp and cool two inches down on a plant that hasn’t been watered recently, likely points towards overwatering. Alternatively, if it feels bone dry, with the soil shrinking away from the sides of the pot, this would indicate severe underwatering.

If you can't tell, lift the pot up – a plant that has just been watered or is retaining too much water will feel noticeably heavier and this could signal a drainage problem. 

Overwatering

This is the most common cause by a wide margin, and it accounts for most of the yellow leaves we're asked about.

Overwatered leaves turn a soft, uniform yellow. They feel limp rather than crisp, and it usually starts with the lower, older leaves before working upwards. The soil stays wet for days, and you may notice small black flies around the pot, which are typically fungus gnats. Whilst they don't cause leaves to yellow, they can help you diagnose the underlying issue that is causing the leaves to turn yellow.

What to do

Stop watering and let the top third of the soil dry out completely before you go near it again. Tip out any water sitting in the saucer or cover pot. Roots left standing in water can't get the air they need, and that's what tips overwatering into root rot and yellowing leaves. 

Check the pot has a drainage hole. If the yellowing carries on and the stems feel soft at the base, slide the plant out and look at the roots. Healthy roots are firm and pale, whereas rotting ones are brown, soft and smell earthy in a way you'll recognise immediately. Trim those away, repot into fresh soil, and water sparingly while it recovers.

Watering needs drop considerably between October and February. A plant that was happy with a weekly drink in July may only want one every three weeks in the depths of winter.

Underwatering

Less common, but it does happen, particularly  during the summer months, or with plants in porous terracotta pots, or anything sitting in a warmer spot through the winter.

Underwatered leaves yellow from the edges inwards and feel dry and papery rather than limp. You'll often see brown, crisp margins on the same leaf. The soil will be dry all the way through and may have pulled away from the sides of the pot. 

What to do

Give the plant a proper soak. Stand it in a bowl or sink of water for twenty to thirty minutes so the soil rehydrates from below, then let it drain fully before it goes back into its cover pot. Once the soil has taken up water properly, return to a normal routine.

Not enough light

Light conditions can often cause yellowing.

Light-starved leaves go pale and washed out rather than deeply yellow, and the plant tends to look leggy, new growth may look smaller than the old, and you may see a distinct lean as it tries to reach for the light source. In turn, lower leaves may yellow and drop as the plant sheds foliage it can no longer support. 

What to do

Move it closer to a window during the winter months. Light levels fall away the further you move away from a window, so a plant two metres into a room in December receives a fraction of what it gets in summer due to shorter days and it may struggle to adjust to less light.

Clean the leaves and the window while you're there, since a winter's worth of dust makes a real difference. If a room simply doesn't have enough light throughout the year, choose a plant that suits it rather than fighting the conditions – snake plants, ZZ plants and pothos all cope well with lower light.

Too much direct sun

The opposite problem! But easy to tell apart once you look at where the yellowing sits.

Sun damage appears as bleached yellow or pale patches on the leaf surface, usually on the leaves facing the window, often with dry brown centres where the leaf has scorched. The shaded side of the same plant will likely look fine. 

What to do

Move the plant back from the window or filter the light with a sheer curtain. Scorched patches won't recover, so remove badly marked leaves once the plant has put out new growth to replace them.

Ordinary ageing

Sometimes a yellow leaf is not a problem at all, and simply part of the natural life cycle.

Plants shed their oldest leaves to conserve water and use less energy. If it's one or two leaves at the very bottom of an otherwise healthy plant, the new growth looks good, and nothing else has changed, this is then just a normal part of the plant’s cycle.

What to do

Carefully remove the leaf with secateurs.

Hunger, or a pot it has outgrown

A plant that has been in the same soil for two or three years likely needs  repotting.

Nutrient-hungry plants go pale overall, sometimes with the veins staying green while the tissue between them yellows. Growth slows, and you may see roots circling the surface or coming out of the drainage holes.

What to do

Repot into fresh soil in spring, and feed through the growing season from March to September. Hold off on feeding in winter, because a plant that isn't actively growing can't use it and the salts build up in the soil instead.

You can read our guide to repotting here.

Draughty spots

If yellowing occurs suddenly and comes with leaf drop, look at where the plant is standing. You’ll typically notice the leaves feel crisp too. A spot beside a front door, a single-glazed window or an unused fireplace can be several degrees colder than the rest of the room, and a cold draught will make a tropical plant drop leaves quickly. Radiators can cause the same shock but in reverse so gently repositioning a plant will usually fix this.

And if you're still not sure, email us a photo – hello@forest.london – and we'll help you work out what's going on.