You might observe that your dragon fruit turns yellow. This usually happens during the summer season or during the growth cycle. I noticed this yellowing of my dragon fruit last year and did not do anything about it. My dragon fruit eventually turned back to green. This year I decided to tackle the situation. I found out through research that applying epson salt will alleviate this problem. Epson salt is basically magnesium sulfate which may help plants grow greener. It help increase chlorophyll production and improve phosphorus and nitrogen uptake all of which help the plant yield flowers and eventually fruits. It is recommended to start applying epson salt a couple of weeks before summer/hot weather to prevent the yellowing of the plants. I hope this is helpful to you. Cheers.