You need to wait until the tops bend over of their own will. Don't bend them over early. Wait until the leaves are quite brown and dry. Then unearth them on a dry day and lay them out to dry - I always to this in my cold greenhouse because of our weather.

After this either tie them in plaits or put them into net bags and store them in a light, cool but dry place. This isn't always easy. Sounds as though your garage may be dark and this will most likely be the problem. I always keep a trug full in the kitchen and they are fine.