spuds in bags

I seem to get scab when I grow in the ground so I thought I would have a go at growing in bags so the question is what size of bag and how many tubers to that bag,
bearing in mind the cost of compost and would a MP compost be OK or would it need additional feed or ph adjusting.
Thanks in advance Eric

 

The yield and quality of my tatie crops is directly proportional to the amount of horse poo I can lay my hands on. The best crop I've ever seen was actually grown in nothing but the muckings out of some stables.

By this token, if I were growing spuds in bags, I wouldn't bother with compost at all. I'd go straight for the manure. The stuff they sell at the garden centres as 'farm yard manure' is already matured. A possibly cheaper option is to order some sacks of spent mushroom compost. I bought a load a while ago on the recommendation of @Zigs. I got an excellent crop of spuds then too but that time I mixed it with my awful clay soil.

 

Still a possibility of scab with spent mushroom compost as lime is used in the casing mixture applied to the top of the bags, but you'll certainly get a tastier crop from using it.

Some varieties are less prone to scab than others

 

Try Santé or Hermes, and avoid King Edwards like someone avoiding a very scabby thing