Have a look at my pictures about huddling and fleecing perlargoniums together last winter. I see you are up in Scotland so, if the winter is severe, it may not work. I also used a plastic grow bag tent against the house,facing south west. During the worst frosts I pegged an extra cover over the front. They kept in bloom there all winter. The others, in a tented huddle, were cut back to about 4-6 inches. If you give them big pots they will literally explode after water granules under new top soil applied. They are still amazing, as my more recent pictures show.