It really depends on the plant Guest. Hardy geraniums can stay in the ground as they are perennials. Pelargoniums on the other hand will need to be taken into the greenhouse and wrapped in fleece to protect them from the cold. To be honest if they are the little ones you buy as plug plants for summer bedding it really isn't worth trying to keep them going just treat them as an annual and put in your compost come late autumn. As to other plants unless we know what they ar we can't help you.