A quick video of how I go about planting potatoes in containers and then taking up a little soil space on the bed the roots are allowed to grow through the holes into the soil beneath. This is how I did it last year and had some amazing crops of 11 pounds of spuds from just 2 seed potatoes. I use 30 litre pots and add about 4oz of fertilizer to the bottom quarter such as Blood Fish & Bone or whatever your fert of choice is. The amount of room each pot takes up is minimal,around 2square feet so the yield per sq ft is remarkable,way more than planting straight into the soil. The reason seems to be that not only do the plants get all the nutrients from the compost,but also they get extra nutrients and moisture from the soil below. I know the compost costs a little but the ease of harvest cancels out the extra expense and the hassle of digging up the crop. Website : http://www.allotment-diary.co.uk Facebook Page : https://www.facebook.com/pages/Allotment-Diarycouk/119640048156011