What I like to do is peel and orange and use orange slices and change them out every other day or so to prevent mold. It gives them nutrients and water whatever you are feeding. But a lot of people blend up there ingredients and freeze them when they make a whole bunch in ice cube trays to prevent it from going bad. I only really use oranges, carrots, mangos, and occasionally potatoes. Potatoes aren't very good because they seem to mould faster than anything.