I wonder if it can be from too much moisture?

Fertilizer that is too 'hot' would also affect the leaves.

When we are in drought (most of the time), my iris don't produce as much bloom. I haven't had dry buds. Hope someone knows the answer.

Similar experience. I had to move an Iris that was already in bud this Spring because of some construction being done near it. Two buds opened, but the blooms were stunted; subsequent buds(3)dried up or got mushy on the very tips and never opened. I assumed it was my careless transplanting.