I have a beautiful Yucca with three trunks, approx. 4 ft tall. I have watered it once a week only, with Baby Bio. It is in a conservatory so has plenty of sun and light. But just recently some of the leaves on the middle trunk are turning brown. Does it need repotting or more water or less water? Approximately what quantity of water should it have? Please help, I don't want to lose it!