Width - I do about 6" wide, maybe a bit wider since I want a good base for my hilling to build up on. Depth - 6-8" or so. How cold is the soil?

Dave

If the soil is cold, wet, and clammy down deep, dig a more shallow trench...maybe 5 inches. Lay your fertilizer in and then add back one inch of soil and plant the potatoes on that. Cover with 3 inches to start and add back more as they grow.

Thanks for the replies.
Soil temp is in the upper 40s at that depth...but we have some warm weather coming and I still haven't gotten around to planting those taters so maybe it will not be an issue anymore.