temp. causing late plant emergence?

Hi. I live in southeastern michigan (zone 5) and I also have pretty crappy clay soil that I've slowly been amending each year. I've noticed that my perennials come up much later (at least a month) than they do in areas surrounding me. I also live about a block away from a large lake and my temperatures here are slightly lower due to lake winds etc. Are the slightly cooler temps causing a slower emergence of my plants or is it possible that the toughness of my soil is causing my plants to fight to get through so much that they take longer? (Once they make their appearance they are healthy.)

Also, I've been kicking around the idea of just digging up everything, throwing all my plants in pots, hauling in 6-7 yards of good topsoil and replanting so the new soil will be on top of the clay and I wont have to dig into it. I know I'm risking losing stuff, but if I just dump new soil around my new plants, it wont alleviate the promplem of them having to emerge THROUGH the clay again next year. Make sense? Or is this a huge bad idea? When would be the best time? Plants I can remember off the top of my head: Lily-of-the-valley Peony buttercup asiatic/oriental lilies mallows lithrum rudbeckia shasta and crazy daisies chameleon plant dianthus potentilla veronica salvia hostas vareigated sweet flag astilbes bee balm gooseneck loosestrife japanese blood grass gayfeather daylilies I'm forgetting some, but that's the idea of what I have to dig up. Thanks!

Curious....

two things, one is the lake keeping temps down, and the other is that clay warms more slowly than other types of soils. Then, of course, there is the amount of sunlight they get (full sun is good), whether or not they are near a wall (wall is good) or at the bottom of a slope (bottom is bad). if you mulch before the soil has warmed up, that is a major difference. On the other hand, your plants probably last longer in the fall.

The only thing you can really do to help them is make sure you mulch after june 15. you can of course dig them all up in october and replant them in a raised bed. Most of them will not mind it. That will speed their emergence by a lot because a raised bed warms much faster.