Why are my plant leaves turning yellow?

Published 2026-10-24 · 8 min read

Your plant leaves are turning yellow because chlorophyll — the green pigment a leaf uses to catch light — is breaking down, and in most homes the cause is water: too much of it around the roots. Overwatering, underwatering, dim light and a missing nutrient look alike at first glance, yet each leaves a different pattern on the plant. Read the pattern and you can name the cause in about a week, without guessing and without repotting everything.

Why do plant leaves turn yellow?

Chlorosis is the loss of chlorophyll that turns a leaf yellow. The yellow was there all along, hidden under the green: once the green goes, the carotenoids underneath show. A yellow leaf is not automatically a sick plant. It is a leaf the plant is no longer supplying with what it needs, or a leaf the plant has decided to retire.

The RHS treats houseplant watering as a per-plant skill rather than a timetable: different houseplants need different amounts of water, and the technique matters as much as the frequency. No single schedule fits both a Monstera deliciosa and a cactus, and none fits a plant in July the way it fits the same plant in January.

That is why a calendar is the wrong tool. A plant in a north-facing hallway uses a fraction of the water a plant uses in the same pot on a sunny sill in June, and the water it does not use stays in the substrate. The question is never "is it Friday", it is "is the root ball dry". Answer that one and most yellow leaves stop happening.

What overwatering does to the roots, and how to stop it

Lift the plant out of its cover pot and look at the drainage hole. If the substrate is dark, compacted and smells of a cellar, the roots are drowning. Take the root ball out, rinse off the wet substrate, and cut away anything black, hollow or soft with clean scissors. Repot into fresh, open substrate in a pot that drains, and do not water for a few days.

Watering less is not the same as watering rarely. Soak the pot until water runs out of the hole, let it drain completely, and then leave it alone until the top three centimetres are dry. A little water given often keeps the whole substrate damp without ever flushing it, which is the worst of both.

Overwatering is the most common cause

Roots breathe. In a pot that stays wet, the air spaces in the substrate fill with water, the roots run out of oxygen and begin to rot. A rotting root cannot take up water, so the plant droops and yellows while sitting in moisture. The symptom looks like thirst and the cause is the opposite, which is why so many yellow plants get watered again and get worse.

These signs usually arrive together:

Several leaves yellow within a week, starting lower down the plant.
The yellow leaf feels soft and limp, not papery.
The substrate is still damp a week after the last watering.
The pot is heavy, and the drainage hole is missing or blocked.
The soil smells sour, or a green film grows on the surface.
The cover pot holds a puddle an hour after you water.

Underwatering leaves a different pattern

Drought moves from the outside in. Leaf margins and tips yellow first, then turn brown and crisp. Leaves curl inward, new growth comes out small, and the pot feels surprisingly light when you lift it. A plant left dry for weeks will drop leaves too, but those usually fall while still partly green, and the oldest leaves go first.

Too little light, or too much sun

Light is measured in lux, and a phone light-meter app held at leaf height settles the question in a minute. Low light means roughly 100 to 250 lux at the leaf for most of the day: a north-facing room, a hallway, or a spot three metres back from a window. In that range most foliage houseplants cannot make enough sugar to keep every leaf. The lowest leaves yellow and drop, and each new leaf comes out smaller and paler than the one before.

Bright indirect light means you could read a book at midday without switching on a lamp, but the sun never lands directly on the foliage. Too much direct sun burns rather than starves: bleached or yellow patches appear on the side facing the glass, often with a brown, scorched centre, within a few days of a heatwave. Moving the plant about a metre back from the window is usually enough.

Which leaves turn yellow tells you a lot

Position is the cheapest diagnostic you have.

Oldest leaves at the bottom, yellowing first: normal ageing, waterlogging, or a shortage of nitrogen or magnesium. Both are mobile nutrients, so the plant pulls them out of old leaves to feed new growth.
Young leaves at the top yellowing first, veins still green: a shortage of iron or another micronutrient the roots cannot reach, often because the substrate pH is wrong rather than because the feed is missing.
One side of the plant only: a cold draught, a radiator, or sun through a single pane.
Tips and margins only: watering, humidity, or salts built up from tap water and fertilizer.

A variegated leaf — the white or cream sectors on a pothos or a Monstera — carries less chlorophyll to begin with, so it yellows sooner and tolerates neglect less well than a fully green leaf on the same plant.

A one-week diagnosis you can do at home

Change one thing at a time, or you will never know which change worked. Use this table as the plan, then give the plant a week before you judge the result.

What you see	Most likely cause	What to do this week
Several yellow leaves, damp soil, heavy pot	Overwatering	Stop watering, clear the drainage hole, empty the cover pot
Yellow edges turning brown and crisp	Underwatering or dry air	Water thoroughly, let it drain, then wait until the top 3 cm are dry
Pale small leaves, long gaps on the stem	Too little light	Move 50 cm closer to the window, or into a brighter room
Yellow or bleached patches on the sunny side	Sunburn	Move about a metre back from the glass
Only the oldest leaf, rest healthy	Normal ageing	Nothing; remove the leaf once it is fully yellow
Roots at the surface, water runs straight through	Rootbound	Repot one pot size up, in spring

A yellow leaf after repotting or a new plant

A plant that has just changed address sheds a leaf or two. Repotting tears fine roots, a new plant comes out of a shaded shop into a bright room, and a move exposes it to different air and different water. Expect some yellowing for two weeks. If it continues after that, the problem is water or light, not shock.

When you do repot, go up one pot size only. A much larger pot holds a much larger volume of wet substrate around a small root ball, which is the quickest route back to the overwatering problem you were trying to leave.

When a single yellow leaf is normal

Leaves are not permanent organs. Most foliage houseplants keep a leaf for a year or more, then withdraw what they can and let it go. One yellow leaf a month on a plant that is otherwise growing is not a problem to fix. What deserves attention is acceleration: two leaves this week, four the next, then a bare stem.

Some yellowing is built into the plant's year. In late autumn, less light reaches the window and growth slows. A plant that was watering-hungry in June needs noticeably less in November, and the commonest winter mistake is to keep the summer rhythm.

What to change this week

Lift every pot once a week. Weight tells you more than the surface does.
Push a finger 3 cm into the substrate. Water only when it is dry at that depth.
Every pot needs a drainage hole that actually drains. A cachepot is a cover, not a container.
Empty the cover pot 20 minutes after watering.
Keep plants off cold windowsills and away from radiators and draughts.
Feed in spring and summer only, and never a plant whose roots are rotting.
Measure the light at midday with a meter app, at the height of the leaves.
Clean the leaves now and then. Dust blocks the light the leaf is trying to catch.

When to act today

The base of the stem is soft, dark, or pulls away from the roots.
The substrate smells sour and stays wet for a week without watering.
Yellowing reaches several leaves in two or three days.
The plant has stopped growing and the pot is solid with roots.
Only the side facing a cold window or a radiator is affected.
White mould spreads across the surface of the soil.