You have to wait for seed pods to develop. It takes a month or two after the flowers have bloomed. The seed pods look a little like big, fat green watermelon seeds but will be clustered where the blooms were. The round part will be attached to the stem and there will be a pointy end sticking up. When the seeds are ripe they will be dark brown and the pointy end will begin to split open. On each side of the split, there are two chambers with a papery seed inside each chamber. Sometimes the seed falls out and sometimes you have to tease it out with a toothpick. Remove the seeds and dry in an open container for a week or two. Store in a cool, dry container.

I grew a bunch of them a few years ago and they finally bloomed nicely this year. As I recall, I started them with seeds in the fall and grew them inside over the winter. I believe they also Winter Sow very well.