Hi Cliff,
I would say that a good gritty compost, around 50% grit, water them now, then again in october and then you will probably not not have water again until you see growth appearing but plenty water while they are making growth.
It is important that once you have watered the compost it does not dry out completely.
Once they are in flower I would add potassium something like sulphate of potash and water that in. Then reduce watering as wet rot is a big problem with some of the reticulate irises and let them slowly go into dormancy.
It is basically the same treatment as for most of the bulbs I show on the bulb log.