Can I plant the seeds in soil or must I dig another bog?
You can plant them in moist soil or keep them in a container where the soil is kept moist.
Is your iris a yellow flag? It is considered invasive. Here is more:
https://plants.ifas.ufl.edu/plant-directory/iris-pseudacorus/
https://www.gardeningknowhow.com/ornamental/bulbs/iris/water-iris-plant-care.htm