Certified GKH Gardening Expert
Camphor trees are prone to chlorosis (yellowing) from nutrient deficiencies and are stubborn for greening up, it takes a couple or three applications of fertilizer a year, and sometimes a couple of years to see good results. They can also be affected by inadequate watering and low organic matter content so that available nutrients are not taken up and translocated throughout the foliar crown, Drip systems are often inadequate and you need to deep water by flooding a couple of times a month. Camphor are native to southern China where there are summer rains. You live in an area with hot dry summer and fall so good water managment is essential, as well as mulching to help retain soil moisture.
An all purpose complete organic fertilizer application in spring and fall is best for sustained slow release fertility.