How to Prune geranium 'Mabel Grey'?
Deadhead regularly

geranium 'Mabel Grey' · Pelargonium 'Mabel Grey'
Under glass grow in a loam-less or loam-based potting compost in full light with shade from hot sun with good ventilation. When in growth water moderately and apply a balanced liquid fertiliser in spring and early summer. A high potash fertiliser should be used when in flower. Water sparingly in winter. Can be grown outside in frost-free areas in a fertile soil. See Pelargonium cultivation for further advice.
Deadhead regularly