I planted out some 'desiree' seed potatoes ten weeks ago. They've grown well - I mulched them to about 40cm using sugar cane mulch and horse manure (and some blood and bone occasionally). They flowered a couple of weeks ago, and the flowers (from first batch) have finished now. I had a dig around in the mulch to see if there were any potatoes growing, but alas, none! There do seem to be some under intial soil layer though (which was about 15cm). From what I can see through the mulch, it's just stem in there. Is this normal?