Yellow leaves mean different things depending on (1) the variety plant, and (2) what other symptoms the plant is showing. Overwatering, underwatering, mineral deficiency, temperature stress, and so on can all be causes. Below, we’ve broken it down to some simple symptomatic math with a solution to get rid of yellowing leaves.
Yellow Leaves + Curling Inward + Drooping or Crisping =
If your plant's yellow leaves are accompanied by curling, crisping and dry soil — your plant is most likely under watered. You’ll likely see older, lower leaves dropping as well. The solution = water your plant.
Yellow Leaves + Fading to Green + or Bright Yellow =
Above is usually accompanied by wet soil, or even fungus gnats if the problem has persisted for a while. Bases of stems may be blackened. These symptoms together mean that your plant is overwatered. Usually lower leaves drop first, although the whole plant may be affected. The solution = repot (to remove soaked soil) and water less, or let soil dry out and water less.
Irregular Yellowing + Sometimes Leaf Deformities =
Irregular yellowing with potential leaf deformities is usually caused either by a pest or a mineral deficiency. If no pests are visible, then this is likely caused by a mineral deficiency, usually calcium or boron. The solution = fertilize once a month, or repot your plant to provide fresh potting soil. Fresh potting soil contains new nutrients.
Whole Plant Yellowing + May or May Not Drop Leaves =
Most likely a temperature issue — it’s either too cold or too hot for your plant where it is placed. This will usually be a more pale yellow or whitish yellow. Temperature will flux around the plant too much or will be obvious, like a radiator or a draft. It could also be a fertilizer issue. The solution = if no obvious temperature causes are present and the soil seems normal, try a little fertilizer.
Whole Plant Semi-Yellowing + Not Dropping Leaves =
A “general malaise” of a plant turning chartreuse means that it’s either pot-bound—the roots have no room to expand—or your plant is in the early stages of a fertilizer deficiency. The solution = repot to a bigger pot, or try a little fertilizer.
Mature Leaves Yellowing Only =
As plants mature and grow, older leaves can age-out, start to yellow, and eventually fall from your plant. This is natural leaf shedding. If your plant is happy and healthy otherwise, and only older, mature leaves are yellowing and dropping, there is no need to worry!