I planted Dahlias last summer and live in St George UT. I am still waiting for some sign of life coming up out of the ground. Do they need warm ground temperatures before sprouting? When can I expect to some growth coming out of the ground?
Dahlias can be left in the ground in zone 8 with some mulch protection. With the extreme cold this past winter that nearly the entire United States endured, it's possible your tubers may have suffered.
Yes, the ground will need to warm to wake the tubers. They also will need moisture. Pull back your mulching and wait and see.
Here are a few links about Dahlia care and wintering over your dahlias.