A yellow leaf does not identify the problem by itself. Which leaves change first, whether the soil is wet or dry, and whether the plant gets suitable light all matter.
Check soil moisture before watering again
Overwatered roots can lose oxygen and yellow leaves, while severe dryness can do the same. Feel or measure the potting mix before deciding what to do.
Notice which leaves are yellowing
An occasional older leaf may be normal. Rapid yellowing across many leaves, pale new growth, or sharply defined spots point to different issues.
Check light, drainage, and roots
A pot without drainage, compacted roots, or a sudden light change can upset the plant. Correct basic conditions before reaching for fertilizer.
Do not fertilize blindly
Deficiencies happen, but fertilizing stressed roots can make things worse. Identify the plant, yellowing pattern, and growing conditions before supplementing. If yellowing began soon after repotting, moving the plant, or changing the watering schedule, that timing is valuable evidence. Give corrected conditions time to work before stacking several new treatments at once.
Sources
- University of Minnesota Extension — Watering houseplants — Watering, drainage, and water-stress signs in houseplants.