Dear Anita, It is good to know you and thank you for the question! So far I didn't germinated Japanese iris seed (Iris ensata hybrids), but I can tell you how I germinate other iris. (I. lactaea, I. pseudacorus, I. × barbata, ...). They are not fussy, just put them in a good soil (e.g. a soil mix you can buy in a garden center). It should not bee too acidic or too basic/limey. Please avoid coir pith. But if you mix it with sand 50-50% will be OK. You can cover seeds with a few milimeters of soil. Oh, and you don't have to use a soil mix for seed sowing. They are easy but will take a little time. I have successfully germinated I. pseudacorus sown in stoney sand with around 20% coir, left them in winter and germinated under a tree. (To be honest I forgot I had sown the seeds). Good luck! Jan Z5a, Hungary