Yellow leaves are a plant's way of waving a flag, but the flag does not say what is wrong on its own. Yellowing has several common causes, and reading the pattern helps you diagnose the real problem before you make it worse. Here is how to figure out what your plant is telling you.

Overwatering: the most likely culprit If lower and inner leaves turn yellow, feel soft, and the soil is constantly wet, overwatering is the usual cause. Waterlogged soil starves roots of oxygen and leads to root rot. Check by feeling the soil: if it is soggy and smells sour, stop watering, let it dry out, and make sure the pot drains. In bad cases you may need to repot into fresh, dry soil and trim away black, mushy roots.

Underwatering Ironically, too little water also yellows leaves. Here the leaves often look dry and crispy at the edges before yellowing, and the whole plant may droop while the soil is bone dry and pulling away from the pot's sides. The fix is simple: water thoroughly and consider watering a bit more often. A plant that dried out severely may drop a few leaves regardless.

Normal aging Sometimes a yellow leaf means nothing is wrong. Plants naturally shed their oldest leaves, usually the lowest ones, as they put energy into new growth. If a single bottom leaf yellows occasionally while the rest of the plant looks vibrant, just remove it and move on.

Light problems Too little light causes slow, generalized yellowing and weak, leggy growth. Too much direct sun can scorch leaves, leaving yellow or bleached patches where the light hits hardest. Match the plant to its preferred light and the color usually recovers in new growth.

Nutrient deficiency If yellowing appears on newer leaves, often with the veins staying green, the plant may lack nutrients, commonly nitrogen or iron. This shows up in plants that have not been repotted or fed in a long time. A balanced houseplant fertilizer during the growing season usually resolves it. Do not overfeed, though; excess fertilizer burns roots and causes its own yellowing.

How to diagnose like a pro Ask three questions: Which leaves are yellowing (old and low, or new and top)? How does the soil feel (soggy or bone dry)? What changed recently (a move, a repot, the season)? The answers usually point straight to the cause. Adjust one thing, then watch the new growth, because damaged leaves rarely turn green again. Healthy new leaves are the real sign your fix worked.