In my Vermont garden, I grow a number of different varieties of German (also called bearded) irises. One variety — a bicolor I inherited a decade ago from my sister– had died. I put a spade into the ground to see if I could discover the source of the problem, and I found that the rhizomes had deteriorated to a loathsome smelly unholy mess the consistency of overripe bananas. It was a truly disgusting situation and one that I had never encountered before. For the sake of garden sanitation, I dug out the decay and some surrounding soil and carried the filth to the local dump.
Later in the summer, I read this sentence in a garden book: "we cannot confirm the folk wisdom that bacterial soft rot in irises can be caused by horse manure." I knew that rot in iris rhizomes could be spread by iris borers, but these irises were borer-free. On the other hand, I had been working the soil with load after generous load of horse manure. So perhaps there's some truth to the derided superstition. In any case, since I switched to fertilizing irises with the abundant droppings of sheep I haven't had a recurrence of the disease. But then again, I haven't been able to re-test the particular susceptible variety–it being an iris now extinct in my garden.
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