I have been reading with interest the thread about 'free' plant offers and someone mentioned overwintering the perennial plants in the greenhouse. I have a) a greenhouse and b) just got a load of perennial 'plugs' which I have potted up and will be outside during our Scottish summer. I will then take them into the greenhouse but I have never overwintered plants in the g/h before. How much water do I need to give them etc? Any tips?