How do I stop my toddler from hoarding?

My 3 year old is constantly picking up random things that are laying around and hiding them under his bed or in his dresser. This has really only just started in the past few months and he doesn't seem to know what to do when confronted about it. I've tried explaining the concept of throwing things away, but he doesn't really seem to understand. I've also tried refusing to buy him things he wants because he already has so many things, but that just makes him angry. We've lived in the same place his entire life so I don't think it's anxiety. What should I do?