Depending on the variety, most geraniums held over the winter require pruning. However, this should be done in the winter months before regrowth begins. I would still prune your plant gently and then add vigorous amounts of a phosphorous rich fertilizer... at least a fertilizer like one here in the U.S. called Miracle Grow which has a 10-52-10 ratio... the middle number being phosporous. If you're watering fairly often they should be fertilized every other watering with a normal 20-20-20 fertilizer and every fourth or fifth time with the one recommended above, since it tends to wash out readily... Good Luck!