When the lush green leaves of the tropical Christmas cactus turn yellow, it's a sign that the plant is not happy with its growing conditions. Tweaking the plant's culture can bring it back to perfect health.
Although we associate cacti with dry conditions, Christmas cacti are actually rainforest plants, and therefore require more humid conditions. Yellow leaves can be a sign that a Christmas cactus is receiving too little water. Do not allow the soil to dry out during active growth, and mist with warm water to raise humidity in dry homes.
The filtered sunlight that is a part of rainforest culture is the type of light that Christmas cacti need to thrive. Placing a Christmas cacti under natural or artificial light conditions that are too bright can result in the leaves fading. Faded leaves often appear yellow. For best growth, place in bright filtered or indirect light.
If you recently acquired your Christmas cactus from a greenhouse, or have moved your Christmas cactus from a warmer location to a cooler one, yellow leaves may be the result of moving stress. As the plant adapts to its new home, new leaves should come in their normal green colour.