I agree with Lynn I would not add the tall sedum unless you were thinking of using them in the area that you have your annuals.
The semps would only work if you planted them on the gravel. I know what you mean about them dying on the stump. the rotting wood stays to moist. That is why I piled the gravel and stone on top of the stump. I learned from all that died. We get a lot of rain before the freezing ice and snow comes every Fall.
