The seed pods will mature in Fall and will actually open up (burst open) as they do. If left alone, they will just cast the seeds on the ground below the plant - if there is any earth below. They will then eventually grow into new plants but it takes a few years. You can harvest them when they "burst open" and plant to create new iris but the seeds should be barely pressed into wet soil. I don't let mine that are in deep water go to seed, so I can't help you with advise in that regards. Normally, I also prune off the seed pods to allow more energy to go to producing more rhizomes as that's the quicker way to get more plants and flowers which is my personal focus.