How come bananas don't blow up in water?

Question

If potassium starts on fire when put into water, why doesn't a banana?

Answer 1

The potassium in a banana is there in the ionic form, or as a singly charged cation.  Potassium metal, uncharged, is the form that reacts vigorously with water to catch fire and spectacularly explode.  In fact, it is metallic potassium going to ionic potassium that is the basis for the reaction.  

Answer 2

Bananas contain water, naturally. The banana naturally has potassium too, so when the banana grows, it dissolves the potassium.