I have had good luck with growing potatos in tires with straw, useing no soil at all,
put your start in the middle of the tire on the ground. cover with straw
when the plant shows above the straw add another tire and more straw
keep doing this I have gotten up to 5 tires or more,
at the end of the season start taking the tires down and harvest the potatos,
you would no beleave how many potato you can get this way and there is no digging,
sorry did'nt see this was already posted