(photograph of Iris 'Cherokee Heritage' taken at NYBG late May, 2005)
Thank you for your prompt response, Alex. I grew up in Michigan. So know iris can grow in the cold. I will see if I can find out about cold hardiness. One more question. The way you describe planting them is exactly the way we would do it out here. What about the rhizomes
freezing when they're so shallow, particularly the first year? Do I mulch? And, if so, how much and with what?
I did a little more research and you are right, it doesn't seem like there is a question of whether the iris are cold hardiness enough. As far as the big rhizomatous iris (German bearded iris, etc.) I've found that they are quite durable even though they are right at the surface of the soil. Up at the New York Botanical Garden where I was a student and worker for two years they have a tremendous spread of bearded iris and I do not remember mulching them at all. They are in an area with a lot of gravel to provide maximum drainage and that is certainly important. I've done some research and what I've found seems to make sense. Do not mulch with leaves, woodchips, or anything equally organic that might hold too much moisture and promote rot. If your new home stays evenly cold through the winter and there is reliable snow cover then I do not think you have to mulch. If you fear that there might be a lot of freezing and thawing spells that might disrupt the iris then I would recommend laying down a single layer of evergreen boughs to provide a light, airy layer of protection. Obviously it would have been more ideal to get them transplanted with enough time to establish some roots in their new home before winter, but hey, some times we just do the best we can given the circumstances.