Each year I overwinter my pelargoniums in dryish compost in a cold greenhouse, usually successfully. I remove any dead and dying growth to try to keep botrytis at bay and water sparingly, avoiding splashing foliage. I don’t have any special varieties to preserve, just that as they are slow-growing I like to get the new season off to a good start.
I also take cuttings and root in a soil-warmed enclosure. I have had mixed success in a gritty compost with botrytis being the problem. Last year I put half the cuttings in just water and that was much more successful so I have repeated that this year. I use those 20 cell units that many bedding plants come in from garden centres in deep trays of water. Shortish cuttings sit in those. Almost all the cuttings I took a few weeks ago are rooting nicely. So when I next feel like an hour in the greenhouse I’ll pot those up and keep them warmish while they hopefully grow on.