I always have the best of intentions when it comes to fall cleanup, but most years it just doesn't happen. There are some things I intentionally wait for spring to do too, like pruning of Roses and Butterfly bushes and cutting back marginally hardy perennials. With plants that tend to die back somewhat in winter it's just easier to wait till spring, and with marginally hardy perennials they often seem to overwinter more reliably when I leave the old growth on till spring. So typically it all just gets done in spring. Normally that works out well, the fallen leaves make a nice mulch for the winter garden, but this past winter I had rodent issues- the leaves also created a nice warm place for them to nest and burrow....and eat Lily bulbs.
There are also perennials I like to leave the seed heads on for the gold finches and others that I leave simply because I find them attractive in the winter garden, like Siberian Irises. Since there is always a fair amount of cleanup I intentionally wait till spring to do, it's often just easier to wait for all of it. Luckily my house and yard aren't visible to neighbors or from the road, so I don't have to be as concerned about it as most folks.
Juli, pre-emergent weed control chemicals (like Preen) typically only effect seed germination, so your Peonies and other perennials should be fine regardless of the time of application. Your picture of your garden is glorious!
