Thanks for the information, Kent. I only have a handful of irises. Some are in a corner of my raised garden and some are still in 2 gal. pots. I use Osmacote in my raised garden in late winter/early spring, so as to have slow-release fertilizer down when I do my spring, vegetable planting. My irises bloomed profusely in the spring, so perhaps slow-release did not do them any harm. I plant lots of heirloom, gourmet garlic in late October/early November, and use the Osmacote again in early October. I don't have to use it where the irises are, since I do no garlic planting in that corner.