The reason for the monoculture of potatoes which made the blight so devastating is that it enabled families to survive on far smaller areas of land than would be required of they were growing - for instance - grain.

The potato produces a large amount of food from a small plot, it can be kept for long periods, it does not require processing - no miller to pay, and it can be cooked easily on a domestic hearth or simple camp fire - no baker to pay, and it will suport life - it has vitamins and if eaten whole, which was quite common, a family would stay healthy.

In areas where vines were grown the use of copper solution to deter blight was bound to be discovered - Boreaux mixture was sprayed onto vines to prevent mildew - so potatoes being grown alongside would be likely to get a covering too, and then there would be the possibilty of the whole field showing blight and dying off, except for the strip alongside the vinyard - the reason eventually was realised, and the technology and chemicals to protect the potatoes were already available.

However - the number of vinyards in Ireland and Scotland in those days was probably about zero, so the situation of grapes and potatoes growing alongside eachother would never occur.