Air drying: roughly one year per inch
The old rule for air drying hardwood is one year for every inch of thickness. It is a generous guess, not a promise. A board two inches thick can be ready in a bit over two years in a dry, breezy yard, and much longer in a damp one.
Air drying stops at the moisture the outdoor air holds, which is usually between 12 and 18 percent. That is fine for a garden bench. For furniture that will live in a heated room, the boards need another stage indoors.
How to tell
- Weigh a sample board once a month. When the weight stops falling, it has reached the air.
- Cut a thin slice from the middle of a board, and test that rather than the end.
- Write the date on each stack. Memory is the weakest meter in the yard.
Patience is the cheapest tool here. The stack will do its work without being watched.