The plant seems heathy and doesn't drop many leaves but the leaves are turning a purple colour. It's about to start blooming and receives minimal sun in the heat of summer. I've had this plant for at least 15 years and the change in colour has started to occur slowly over the last 2 years. What's up?
Certified GKH Gardening Expert
Purple coloration is usually due to onw of two things. This can be caused by cooler temperatures, or the more likely culprit... Lack of phosphorus. It is recommended to feed these occasionally.
This article will give you more information: https://www.gardeningknowhow.com/ornamental/cacti-succulents/christmas-cactus/advice-for-christmas-cactus-care.htm