If it was me growing them, I would use what everyone calls the 5:1:1 mix. Sweet potatoes like a moist soil, but insist on good drainage, and that particular soil fits the bill nicely. You can read about it at the link I left below.

I would also employ a wick at the container bottom to drain excess water - until the container is well-colonized by roots.

Al

Here is a link that might be useful: More about soils

Al, thanks a lot . Im trying different mixes this year. bill