As the potato seed produce sprouts, remove all but the topmost four to
ensure that they receive all the goodness of the seed potato. The ideal
sprout length at planting time is 2.5cm (1in) although this is not critical.
What is critical, is that the sprouts are green and not white coloured.
White sprouts are caused by not enough light.

"Bertie Doe" wrote in message
...
I know you shouldn't allow potatoes to stay too long in sunlight when
you're digging them, as they go green. But now, when they're developing
shoots in trays - sun or shade? TIA
Bertie