In the Garden:
Iris rhizomes develop foliage in one direction or the other, so planting in groups with the foliage pointed outward works best.
I've been busy redoing the bearded or German iris bed. I find this is a necessary task every few years when the plants become crowded and start blooming less. And late summer is the perfect time to transplant iris.
Dig, Sort, and Clean
I dig up iris clumps and discard the tough old rhizomes that have lost their strength. I also discard those rhizomes that have the dreaded worm-like iris borer or its signature tunneling damage. Even though the borers may be gone, the tunneling opens areas to infection from rot organisms. I'm ruthless about removing blemished foliage and trim the remaining healthy leaves or fans to about 5 inches tall. Because of the danger odf spreading infection of insects to new plants, I always throw out the iris trash and don't compost it.
Cleaning Up Rhizomes
Once I have the rhizomes ready, I dip each in a solution of water and ordinary household chlorine bleach (1 part bleach to 9 parts water) and spread them out to air dry for several days. Of course, I try to keep each variety separate, with tags marked in indelible ink.
I choose a new site for the iris transplants in full sun and provide good drainage, meaning not soggy in the winter time. I like planting bearded iris on a slope or a slightly raised bed to ensure good drainage. Iris grow best in a rich soil that is not too acidic. I add compost and loosen the soil 1 foot deep.
The Right Way to Plant
I plant the rhizomes in triangles, 3 of one type set about 1 foot or more apart with the leafy end pointed outward. For each piece, I make a ridge of soil several inches high. I align the rhizome on top of the ridge and bury its roots down deep on each side. In the process, the soil jiggles around and partially covers the rhizome. I press firmly to compact the soil and water thoroughly. This rinses some of the soil off the top of the rhizome. It ultimately settles roughly at soil level, partially exposed. If I cover the whole rhizome with soil, it is more likely to rot and not flower.
I add a label and mulch in between but never over top of the rhizomes.
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