Yellow leaves on plants can indicate different things depending on the variety and what other symptoms the plant is showing. Here are some common causes of yellow leaves on plants:

1. Overwatering or underwatering: Giving your plant too much or too little water can cause yellowing leaves. Overwatering can suffocate a plants roots, while underwatering can cause the leaves to shrivel and become crispy.

2. Nutrient deficiency: Yellowing happens when something interferes with a plants chlorophyll, which is the plant pigment behind their beautiful green color. A lack of essential nutrients in the soil can cause yellow leaves. Essential minerals are absorbed through the soil, and different plants have different nutrient requirements.

3. Pest or fungal infection: 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. Fungal or viral diseases can also cause yellowing leaves.

4. Temperature: Whole plant yellowing (may or may not drop leaves) is most likely a temperature issue. Its 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.

5. Natural leaf shedding: As plants mature and grow, older leaves can age-out, start to yellow, and eventually fall from your plant. This is natural leaf shedding.

To fix yellow leaves on plants, its important to identify the underlying cause and address it accordingly. For example, if the cause is overwatering, reduce watering frequency and ensure proper drainage. If the cause is nutrient deficiency, fertilize the plant once a month or repot it to provide fresh potting soil. If the cause is a pest or fungal infection, treat the plant with appropriate pesticides or fungicides.