My first one was by mistake I lost the knife doing yardwork the place was a jungle have to do lots of clearing weeds & vines dominate. Before we moved in.
Auntie too old for yardwork & never hired yardmen. It was above ground hidden by weeds found it 2 years later. Open position blade covered in deep rust. Later I ordered two #12 one carbon & one stainless 23.00 each took blades off & buried them in Rich volcanic soil. 7 months it rained a lot during those months. When I pulled them out covered in dirt washed them sanded with 80 grit could tell plenty spalting. It was windy & sunny so hung them on line to completely dry. Once dry continued sanding 80, 100, 150, 220, 320, 400, 600, 1,000, 1,300, 1,500, 2,000.
Picture of carbon that lost two years with new carbon blade it got a few spots on it laying on workbench in open air garage. So cleaned up thinned it put very sharp edge.
The wood was dry but buried in moist dirt became feeding ground for fungus & bacteria. They even break down fallen trees in rainforest. Buried for 7 months up here more than enough time. Maybe with the rain 5 months enough.