I dont grow these but my grandad has hundreds.
He uses a balanced fertilizer and mixed at 1/4 to 1/2 recommended strength and applies it weekly during the active growth. He also uses a low nitrogen and high phosphate in autumn as he reckons it makes it bloom better and hardens the growth off. If they are in pots he flushes out every two weeks or so. As for watering he never lets dry out... Hope this helps