Granger wrote:When/how to harvest poppy so one gets the opium pod?
I can't pin down the "when", but after it's passed the "how" is as simple as harvesting the crop like you would do with any other crop. The only thing that changes between getting a flower output and a pod output is the item that's left on the ground once the action is complete.
As for "when", I've just been leaving my field of poppies for two or three days after they've all matured and I'll almost always end up with 3-6 pods from about 33 plants.