I don't grow anything other than perennials, even gave up on tomatoes for the most part because of the short growing season and hail. Perennial beds are it for me!
I've always planted a piece of divided peony back in the same spot, have added compost to the hole but re-used most of the original soil with no negative results. I've wondered why it'd be a bad idea to replant a piece in a spot that it's done well enough to warrant division....I can see not replanting in a spot where a plant has struggled or where it was diseased.
Is the advice for not replanting iris because or borers or another disease? I have a bunch that need to be divided, waited too long this fall so it'll have to be next summer.
