If I might, I'd like to add a few words to this thread........in the past, I always used a "mix" of 10-10-10, and 0-45-0...which gave me 5-27-5.....about the time the new growth started, and again, just after bloom. The Re's also got a couple sprays of "foliar" fertilizer every season . I followed the established wisdom that the nitrogen should be applied very sparingly,and that more phosphates meant more bloom. I always checked my soils ph with a "home tester" to keep it in the neutral range ..........and , I had reasonable success, but, every year I had a higher incedence of rot...usually the fungal sorts, but, some bacterial, also.
What I found was......a buildup of phosphates......a low amount of nitrogen......and the ph level was only "close" to optimum....not "exactly" so. I had all the beds checked by the AG service, and found that what I needed to do was add MORE nitrogen, NO phospate, and NO potash, plus, a LOT of lime.....so, my advice is, before you add ANYTHING to the iris beds.....GET YOUR SOIL TESTED !!
