The most common causes

Yellowing is a generic stress signal, so the trick is reading the pattern alongside the soil. Use this table to match what you see to the likely cause and the fix.

CauseTell-tale signWhat to do
OverwateringSoft yellow lower leaves, soil wet for days, sometimes a sour smellLet the top inch or two dry, improve drainage, empty the saucer
Natural agingA single oldest leaf yellowing slowly while the rest look healthyTrim it at the base; no other action needed
UnderwateringWhole plant fades, soil bone dry and pulling from the pot, crispy edgesWater thoroughly until it drains, then keep evenly moist
Too little lightSlow, even fading; leggy, stretched growth toward the windowMove to brighter indirect light
Nutrient deficiencyEven pale yellowing across many leaves, often with green veinsFeed at quarter to half strength during active growth
Root rotYellowing plus black, mushy, foul-smelling rootsUnpot, cut away rotten roots, repot in fresh dry mix
Sudden draft or coldYellowing after a move near a vent, door, or cold windowRelocate away from drafts and temperature swings
PestsStippled or speckled yellowing, webbing or sticky residue underneathWipe leaves, isolate the plant, treat with insecticidal soap

Overwatering: the number one cause

Across nearly every common houseplant, overwatering is the leading reason leaves go yellow. Roots need air as much as water, and when soil stays saturated the oxygen is pushed out and the roots suffocate and rot. The plant can no longer move water and nutrients up, so the oldest leaves yellow and go soft first.

Confirm it by feel and pattern. If the lower leaves are soft rather than crispy, the soil is still damp several days after watering, and the pot has poor drainage or sits in a full saucer, overwatering is almost certainly the driver. Let the soil dry to the top inch or two, water only then, and the yellowing should stop spreading within a week or two.

Light and nutrients: the slow fade

When yellowing is gradual, even, and spread across many leaves rather than starting at the bottom, suspect light or feeding. Too little light slows chlorophyll production, and you will often see stretched, leggy growth leaning toward the brightest window. Moving the plant to brighter indirect light usually halts the decline within a few weeks.

Depleted soil is the other slow driver. A plant kept in the same pot for a year or more can exhaust its nutrients, producing pale leaves with a faint green vein pattern. During the spring and summer growing season, feed at quarter to half strength every two to four weeks, and repot into fresh mix if the soil is old and compacted.

When yellowing is normal and when it is not

Not every yellow leaf is a problem, and chasing a phantom one can lead you to overcorrect and harm a healthy plant. The single oldest leaf at the very base of the plant turning yellow and dropping every so often is simply senescence, the plant retiring a leaf it no longer needs to fund new growth at the top. If the rest of the foliage is firm and green and only the bottommost leaf is affected, trim it off and do nothing else.

Treat it as a real warning when the pattern is wider or higher up. Several leaves yellowing within a week or two, new leaves emerging yellow or pale, or yellowing that climbs up the plant all point to a watering, light, or root problem that will keep spreading until you fix it. The texture is another tell: soft, limp yellow leaves usually mean too much water, while dry, brittle yellow leaves with crispy edges usually mean too little. Read the texture and the spread together before you change anything.

Find the fix for your plant

Yellowing looks similar across species but the exact triggers differ, so go to the article written for your plant:

Start by checking the soil moisture and the pattern of yellowing today. If the soil is wet and the lower leaves are soft, ease off watering and fix drainage first, since overwatering is the most common cause by a wide margin. If the soil is dry or the plant is in a dim spot, adjust watering or light accordingly. Then remove the fully yellow leaves and give the plant two to four weeks of stable care before judging the result.