A cactus that is exposed to an excessive amount of light is often the cause of the plant turning yellow. Other reasons why it may be yellow are disease or being watered too much. Reducing the amount of light and water exposure may halt the progression of the color change.
There are several different species of cactus plants, and each has its own sensitivities to external and internal growing conditions. In general, cactus plants thrive on sunlight. However, there are certain species that turn yellow when exposed to a lot of light.
Plant watering and soil conditions are other reasons why a cactus changes from green to yellow. Some cactus plants receive too much water. Adjusting the amount of water helps to alleviate the stress on the plant. The potting soil could be in need of a bit of fertilizer. Cactuses do not normally require extra fertilization. However, some cactuses absorb more nutrients than others. In the case of a yellowing plant, adding fertilizer to the soil might help it to get the extra nutrients it needs.
If a decision is made to repot the plant, the fertilizer would be added in at that time. Fertilizing a cactus plant is recommended every one to two years.