Earthing Up Potatos

Hi here goes for my next beginers questions :o

I have 10 Vivaldi potato plants from seed potatos which have come through and now have 2" or so of growth, do I need to earth up now or later? & what is the purpose of earthing up potatos? how do I do it? :confused:

 

Potatoes can grow near to the surface and, if they break through, sunlight will cause them to go green. These are poisonous to eat - they won't kill you but will make you feel ill! The purpose of "earthing up" is to give the spuds room to form in the dark. Also, they have more room to grow so you will probably get a bigger crop. A modern practice is to lay down black polythene top achieve the same effect (but I have not tried this myself)