I let the poppy heads dry off and then shake them into an envelope...poppy seeds are very tiny...but if you leave the poppy heads on the plant they will fall out on their own and re-plant them selves.

Depending what sort of Poppies they are, they may not come truefrom seed.For example, if they are Oriental Poppies, they tend to revert back to field Popy type flowers

When the seeds are ripe the top of the seed capsule develops a ring of little holes for the seeds to fall out of. You need to wait until this happens but then don't delay as the wind will then bend the stems and the seeds will fall out.

Thank you.