Overwatering cannot be diagnosed from yellow leaves alone. The strongest clue is the combination of plant symptoms with potting mix that stays wet too long, damaged roots, or poor drainage.
Check moisture below the surface
Check several centimeters into the potting mix with a finger or clean tool rather than judging the surface alone. If it stays wet for many days after watering, the plant may be receiving water faster than it can use it.
Read leaves and stems together with soil condition
Yellowing, soft leaf drop, watery stems, or stalled growth can accompany excess water, but those symptoms have other causes too. The diagnosis is stronger when the potting mix also remains wet.
Check drainage holes and roots when needed
A pot without drainage or a saucer left full of water deprives roots of oxygen. If the plant worsens, careful inspection may reveal brown, soft, foul-smelling roots that need cleanup and a better-aerated mix.
Adjust timing instead of adding more water
Let the mix reach the appropriate dryness for that species before watering again. Improve light, drainage, or potting mix if it dries too slowly; a fixed calendar does not fit every season.
Sources
- University of Minnesota Extension — Watering Houseplants — Watering, drainage, and water-stress signs in houseplants.