PlantLife Online

Answer

As an arborist I would prefer to see yellowing to browning. Inconsistent, non-uniform yellowing generally tells me there is some sort of abiotic condition causing the leaves to turn. My first thought would be to check soil moisture, dig down or use a soil probe to inspect the soil moisture of the rootball, be sure the roots are not sitting in water or bone dry. The soil should be slightly moist but not dripping. Often evergreen species like the Q. agrifolia will yellow when they are over-watered or it could just be that they are getting ready to drop as a stress response to a climate condition. Keep the watering consistent allow the soil to dry between watering, water deep and through avoid partial, inconsistent waterings and avoid fertilization. Without knowing the species and exact growing condition it's hard to say the exact cause of the yellow leaves, I would keep an I on it, if it continues to yellow send us a photo.