Hi Teri,

Since you just planted them this spring, it's probably from the transplant. You will probably not get that next year, although siberian irises often get brown tips.

Nothing to worry about. I wouldn't be concerned over the soil, siberians are quite adaptable.

It is fall where you are, and the siberian irises should be starting to get ready for their winter sleep. The leaves will go completely brown, at which stage you can cut them off close to the ground. Don't pull them off as that can damage the rhizomes. Next Spring, the leaves will appear as little green points. Don't let them get too wet in winter. They require reasonable drainage and to moist garden soil all year.
Cheers, Jan in Australia