I have about 30 geraniums growing in pots in the garage. They’re 1 to 2 years old. They have even flowered during the winter. My questions is this: when should I prune them down and start watering and feeding them? We have given them a little water in late February or March, but this year they have been blooming much longer.
You could have pruned them in the fall when you put them into the cold storage for the winter.
I would go ahead and clean up and prune the plants now. Remove any brown or dead leaves and cut the plants back by 1/3.
When the last danger of frost has passed the plants can be placed back outdoors.
Fertilizer can be applied when the plants are actively growing.
Here are some links to help you.