First, let’s be clear: we are referring to Bearded Iris in this discussion. The myriad of other lovely Iris varieties come with their own set of operating instructions.
Our last two blog posts generated a number of very worthwhile questions. After doing a bit of reading on the subject, I came across a couple of useful bits of information. The first is a series of photos on planting Bearded Iris, see below. These come from William Shear’s, “The Gardener’s Iris Book” (Taunton Press, 1998), page 43. How deep should the rhizome be? We are in agreement with Mr. Shear on this question. “It depends,” he writes. “In light-textured soils, it can be covered by as much as 1 (one) inch of soil, but for average to heavier soils, the top of the rhizome is best left exposed to the healthful influences of sun and air. Remember that the rhizome is a stem, not a root, and needs to breathe!” You can see in the third photo below that the top of the rhizome is still peeking through the soil.
On the subject of trimming the foliage, I found a bit of tidy wisdom, the kind you keep clipped into your pocketbook, or saved on our phone, for easy reference. This comes from, “A Guide to Bearded Irises: Cultivating the Rainbow”, by Kelly Norris (Timber Press, 2012). In his myth-busting section he addresses the question of trimming. “Myth: Bearded irises are so much work. You have to trim the foliage back every summer!” Mr. Norris reassures us that in fact this may be an “unnecessary chore”. There is no real need to trim the foliage in the summer, except that during dividing and transplanting shorter foliage eases the handling of the plants. He reminds readers that “needlessly trimming the foliage back in the middle of the season actually breaks an iris’s dormancy, kick-starting foliar production. This can take away from root mass accumulation and even from reserves meant to support flowering the next spring.”
The long and short of it is to plant shallow and leave the leaves alone. Thanks for reading and happy gardening!