Why are my plant’s leaves turning yellow?
Yellowing is the single most common houseplant complaint and it has about six causes that look superficially alike. Sorting them takes three observations: which leaves (lowest or newest), how they feel (soft or crisp), and how long since you watered.
The causes, and how to tell them apart
Overwatering / early root rot most common
How to tell: Lowest leaves first, uniformly yellow, soft and limp rather than crisp. Soil is still damp several days after watering, and often smells sour. Sometimes fungus gnats.
What to do: Stop watering and let the pot dry well down. Check that the drainage hole is not blocked and that the pot is not sitting in a saucer of water. If the soil stays wet more than a week, unpot and look at the roots — healthy roots are firm and pale, rotting roots are brown, soft and pull apart easily. Cut those off and repot into fresh, faster-draining mix.
Underwatering common
How to tell: Yellowing arrives WITH crisping — dry, papery edges — and the whole plant looks slightly deflated. Soil has pulled away from the sides of the pot and water runs straight down the gap.
What to do: Soak thoroughly until water runs from the drainage hole, ideally by bottom-watering for 20 minutes so the rootball rehydrates evenly rather than the water tunnelling down the sides.
Natural leaf aging common and harmless
How to tell: One or two of the OLDEST, lowest leaves, while everything above looks healthy and new growth continues.
What to do: Nothing. Plants retire their oldest leaves to fund new ones. Remove it once it is fully yellow.
Too little light common
How to tell: Gradual, widespread pale-yellowing rather than dramatic drop, plus long bare stretches of stem between leaves and any variegation fading toward plain green.
What to do: Move it closer to a window. "Bright indirect" in practice means somewhere you could comfortably read a book all day without a lamp.
Nutrient deficiency less common indoors
How to tell: Yellowing between the veins while the veins themselves stay green, usually on NEWER growth. Typically on a plant that has been in the same soil for years.
What to do: Feed at half strength during the growing season, and repot into fresh mix if it has been more than two or three years. Never fertilize a bone-dry pot — water first.
Cold damage or a draft seasonal
How to tell: Sudden yellowing after a cold snap, often with greasy grey-green patches, and worst on the side facing a window or a door.
What to do: Move it away from the cold glass or the draft. Damaged leaves will not recover; watch the new growth instead.
The same watering schedule causes both of the top two causes
Overwatering and underwatering head the list above, and they are not opposites so much as the same habit meeting different plants. Across the species tracked here the summer interval runs from 3 days to 21 — a seven-fold spread. A fortnightly routine is neglect for one of these and a slow drowning for another. The extremes:
| Species | Water roughly every | Let it dry |
|---|---|---|
| Boston fern | 3 days | never fully — keep evenly moist |
| Citrus | 4 days | top 2" |
| Calathea | 5 days | never fully — keep evenly moist |
| Peace lily | 6 days | top 1" |
| Croton | 6 days | top 1" |
| Aloe | 14 days | all the way through |
| String of pearls | 14 days | all the way through |
| Snake plant | 18 days | all the way through |
| Ponytail palm | 18 days | all the way through |
| ZZ plant | 21 days | all the way through |
Summer figures, and a starting point rather than a schedule — the pot, the light and the season all move them. The check is the soil, not the calendar.
By species
The likely answer differs by plant — these species have their own version of this problem:
Plantroster compares this month's photo against last month's, so slow changes — the ones you stop noticing because you see the plant every day — get flagged.
Open PlantrosterOther problems
General horticultural guidance, not a diagnosis of your specific plant.