1) after they've flowered and the haulms (shoots and leaves to you and me) have died down - these potato varieties don't flower
2) for earlies, harvest 37 weeks after planting - I can't quite recall exactly when I planted them (I promise to write this on a calendar next year...)
3) have a 'furtle' in the soil and see if you find any - I planted all my potatoes in bags, so have limited furtle space
So, I've decided to add my own suggestion to this list:
4) when virtually all the haulms have been eaten by slugs or snails and you fear your potatoes are next on the menu.
But my fears were unfounded when we discovered a respectable harvest in both sacks, certainly much better than last year.
And the suburban veg plot have been yielding many other harvests recently: onions, runner beans, carrots, chillis and garlic but the most surprising was a parsnip that grew from seed I sowed in 2008... The leaves started to get really big after a couple of months so I pulled it up to reveal a root the size and shape of a cricket ball with lots of long thin roots growing in all directions.
I'm already planning the winter veg plot - I have 2 varieties of leeks in the ground and have started to sow savoy cabbage and kale seeds for transplanting in September. I also hope to time a new planting of potatoes so that I get a Christmas day harvest.
