Lovely to have some help but from what I've read Sept. is the month to divide Siberians, or spring. We gardeners break the rules and if I were to divide now I'd make sure to get a large root mass. Good luck. Let us know the results.

Your zone 8 summer weather is alot different than my zone 8 summer weather. I am jealous that you can grow siberians. The long time natives in Las Cruces don't even try siberians. Good luck with your project. I'll be anxious to hear of your adventures.

Siberians are tough as nails. Although conventional wisdom usually dictates fall, I've never had a failure doing it any time the need to arose. Been an unusually cold and wet spring, first days of summer here, too, and the Siberians are still blooming. I'd at least wait until the blooming's over if that's the case with yours, too... and cut down the stalks and trim back the foliage a bit to make digging up, handling, and dividing easier. Be sure to have a sharp shovel - I've occasionaly had to separate a big clump of them with a pruning saw.

Prepare their new spot in advance and water them in.

ok, so the deed is done. Thanks for the replies. This iris was so huge, that I got 6 gallon sized divisions out of it. The middle got tossed out. It wasn't too bad to dig it up because i had manly husband help. The weather is cool, but I have the hosed stretched out to the bed, so i can water daily for the next week or so. I bought a bunch of 4 inch pots of ladys mantle for the front of the bed. I think it will be quite pretty next year. Thanks again.

It sounds wonderful. Lady's Mantle is a perfect companion plant for Siberian irises.
Renee