Re: Freezing/thawing measure
When I grew iris in Minnesota (and a practice my sisters still follow
today), we would cover the rhizomes with sand as they emerged due to the
freezing and thawing. The sand would work its way down and around the
rhizome, and they would remain covered.
We also would cover the iris with straw with the first snow (burning that
and the dead foliage off in the spring).