If you can provide light, frost-free conditions, it’s easy to over-winter pelargoniums where they often flower through autumn and well into winter. Ideally, zonal and fancy-leaved pelargoniums (often called geraniums) need a minimum winter temperature of around 5C (40F), although they’ll survive cooler conditions if the atmosphere is dry. Through the winter months water sparingly to keep the compost just moist as, when too wet, root rots can set in.
Plants can be grown for several years to produce large specimens for use in outdoor containers over the summer, but after a couple of years they can start to get tall and leggy.
To help keep the plants bushy and compact it’s a good idea to prune the older, taller shoots down around this time of the year. From now on the days start to get longer and this, with a little gentle heat, will encourage new shoots to develop from dormant buds low down on the stems. Pruning tall plants hard back does look a little drastic, but it you don’t the base of the plants will soon become bare and woody. After pruning, to encourage new growth you can top dress with some fresh compost and gradually start to increase the amount of water as new shoots start to grow over the coming weeks.