In colder USDA hardiness zones, it is best to pot up geraniums growing in the yard and move them somewhere undercover.
To winterize geraniums, but particularly cuttings, keep your tender pelargoniums somewhere frost-free over winter, otherwise the cold weather will kill them off.
A heated greenhouse, porch or cool room are all ideal as long as they have good light levels to keep your cuttings healthy.
If your greenhouse is unheated, cover your pelargonium cuttings with a frost cloth blanket like this Alpurple one on Amazon. Remove the cover when the temperature rises as trapped condensation may turn the leaves mouldy.
Your pelargonium cuttings will go dormant and stop growing in winter, so they only need watering if they start to droop – this may only be two or three times before they grow again in spring.