We got a new roof put on a week ago, and the roofers put tarps over my iris, could that be what caused them to do this?

Split and transplanted them about 5 weeks ago.

How long did the tarp cover the irises? Being deprived of light would be a cause for the yellowing leaves.

pirl said:How long did the tarp cover the irises? Being deprived of light would be a cause for the yellowing leaves.

They were completely packed up and done in about 4 hours.

I can't imagine how they could have been damaged so much in such a short time. Pictures would help.

Possibly when you divided them, some of the rhizomes were cut in half and those may die, the ones not cut should be OK, It is usually better to split Siberians a bit later, like in August. Siberians like an acid soil, and are heavy feeders. Keep them watered.

What color was the tarp ? If it was a "dark color", even a short time will "overheat" any leaves that are touching it. IF the sun was out, that is. To help the newly "transplanted", I always use the "Miracle Grow for acid loving plants", a few times , after transplanting.