Hi Idaho. Welcome to our group!!
You're absolutely right to be getting those babies into the ground -- especially if they're in a somewhat protected area. Irises generally need five to six weeks to develop new roots before the ground freezes -- do you think you have that much time? I'm afraid that allowing them to sit in the house over the winter, they would dry out and be of no use to you at all. An alternative would be to plant them in pots to keep them over the winter. That may be impractical if you have a lot of rhizomes.
Regarding bonemeal -- I've not placed it in the hole, but sprinkled it around the rhizome on top of the ground, and mixing it in a little bit. It did make a difference in the size and health of the rhizomes the following Spring. I did use a handful of bonemeal on top around the rhizome -- I doubt that a handful would be too much to put in the bottom of the hole, especially if the hole was larger than the rhizome. I don't think you need be overly concerned about this -- it isn't an exact science. If you think a full handful is too much, just use a little less. The Iris will appreciate whatever you use!!
Where did you get your rhizomes? Tell us which Irises you got............
