Full moon and after. New moon when above ground, full when its below ground.

Sorry Wyllie but that info is not completely correct. Guest please refer to my blog but over the next month you can plant your potatoes (start with the first earlies) at the following times:

29 - 31 March - which IS full moon
7 - 9 April
16 - 18 April - new moon
26 - 28 April

If you are following the lunar/biodynamic way of growing then if is as much to do with which constellations the moon is passing through/in front of (The moon doesn't actually pass 'through' anything!)

Sorry GoY seems to be playing up and posted my comment twice :-)

I was going by the old farmers. There was one who went against the system last year, and he ended up with major erosion problems all winter. It comes down to looking when the old guys plow and plant. If you do the same, you'll have sucess.