Worm castings are the yogurt of the soil world and technically they’re a “living” product. Full of micro-organisms, vermicompost when fresh will continue to “grow” if stored properly. If you have them in a plastic bag, make sure to poke some air holes. The aerobic bacteria need air. If the castings dehydrate completely the bacteria will die. The fertilizing quality of castings remains the same wet or dry. In fact you can greatly increase the microbial content by brewing tea with an oxygen bubbler, but that’s another post. We suggest you store casting as you would a root vegetable. Look for a cool dark area, check the moisture content and you can use them as you see fit.