France 
Thank you for your reply,i recall as a lad that in my summer holidays we worked on a farm and use to pick potatoes then the tops were just startying to die off is this right.
13 Jul, 2010
Answers
Rule of thumb is 13 weeks from planting to harvesting for early potatoes 17 weeks for main crop. Our potato hames often don't die off completely. Locally the farmers spray them with sulphuric acid to kill the hames off - makes you wonder doesn't it!
13 Jul, 2010
This is what normally happens with earlies. When the tops start to die down you harvest them. This can happen without them even flowering.
With main crop, which I don't normally grow, you leave them to grow for far longer and I think they go on growing until autumn unless affected by blight.
13 Jul, 2010