The grapes were all dead. There were no animals or people in that region. It was barren. Merlin moved SE to the headwaters of the Rhone and planted grapes in a more climatologically welcoming regions ~ Beaujolais!
He stayed there a while, then withdraw back to the West and replanted the grapes there.
All of this is covered in the Annals of the Kings of Britain as well as the Arthurian folios preserved in Eastern France (which show Merlin much more important than Arthur).
(NOTE: I used modern English names for these people and places. Myrrdhin and Ad are probably more correct ~ but my favorite part is where Myrrdhin seals Ad in a cave and lets him rot. So much for giving away land to the Saxons).
> ... Arthurian folios preserved in Eastern France (which show Merlin much more important than Arthur).
“Orlando Furioso” is the literary work referred to. Merlin is substantially more important; in fact Arthur is barely mentioned. The story centers on Orlando. One part that was interesting was that Merlin foresaw that Excaliber would be broken and had the Lady of the Lake forge 2 copies, the second to replace the one that would break.