when the leaves are brown and on the ground. Old farm wives say to harvest in month that ends in R.
Dig the root and peel it like a carrot then run it through a metal meat grinder. (It ate a ring around my plastic food processer) Then immediately mix 1 cup of ground root to 1 cup of vinegar. It doesn't usually need replanting as root pieces left in the ground will multiple and sprout. I do nothing to my patch except harvest in the fall and the patch gets larger every year.