Does a Hibiscus need to be fertilized in order to bloom?

I have a tropical hibiscus which will remain in the pot & indoors during the winter & will bring outside in the summer. Everything i read about them says they must get fertilizer. The only reason I am growing them is they are a delicacy to my tortoise & obviously I cannot feed them to her if pesticides are used. Are their any natural non toxic additives I can use or will they do okay with out fertilizer?