Energetic "shelf life" of herbs and spices?

All that money bowl talk reminded me of a question I've wanted to ask for a while. How long will the herbs and spices added to a money bowl keep up their energy?

I made the bowl on January 2nd and don't plan to take it apart and reassemble until January 1st, but I do add things to it regularly.

Would it be advisable to fully exchange the herbs and spices at some point, and where does that point lie?

Thanks!