hi

i am new to austin texas .. i think i have few salvia greggi alba sage variety in my yard which bloom white flower . It was dry and half lost leaves in winterstorm .. i pruned them , mulch and put some miracle grow plant food.. shake and feed .. it started to grow big and green and beautiful white flower all over since 45 days .. until last week i start to see leaves getting yellow in the inside centre part of plant or lower sides .. dont know why its happening ... i changed nothing same sprinkler setting since one year .. please help