how long does it take a compost pile to decompose
When I first ventured into composting, I found that nut waste was one of the most difficult things to deal with. After some research, I found that chemically it can take 2 to 3 years for the shells to decompose. My recommendation would be to grind up the shells if you are adding them to your compost pile. They will still take time to break down, but it adds a nice bulk to your compost.