How deep was the trench and how high was the earthing up? How long ago were they planted?
We once had a student here "who'd no tak nae advice" and planted our spuds a good 18" deep - nothing at all happened that year, then the following year we had a crop - weird
I usually plant my potatoes about 5-6" deep (12-15 cms
) but I don't earth them up until they have grown a bit ie appeared above the surface. Then I earth them up bit by bit, so unless there's a frost forecast there are always a few leaves peeping out.
I think if they are planted very deep it could take them quite a long time to appear. Why not gently scrape some of the soil away from the sides of some of the seeds and see what is going on?