Answer: Mid-August is a great time to dig and divide irises. You can do so all the way up through the middle of September and they will have ample opportunity to settle in before winter arrives. If your Japanese irise are overcrowded or if they are not getting enough sunshine, they can fail to bloom. I'd dig and transplant them. Amend the soil prior to replanting and be sure to give them 4-5 inches of space so the roots won't have to compete for moisture and nutrients. Feed your irises and your delphiniums in the spring with a 10-10-10 general purpose fertilizer (or a 20-20-20, if that's more convenient). Best wishes with your garden!
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