How often should I put plant food in my wave petunias and lillies?

i pit those miracle grow sticks that are green in my flowering plants once a month.. depending one how big the pot is.. read the directions on the boxes.. it depends on the brand you buy and how big you pot is

How often should I put plant food in my wave petunias and lillies?
It depends on what kind of fertilizer you're using. For most inorganic fertilizers like Miracle Gro, every 2 weeks is fine. Read the box.