When to dig up tulips?

I dug some up too early last year and they rotted. This year I did the same with a small grouping that had the foliage all browned so I thought it was ok to do it, but they didn't have their skins hardened yet and they look "rottie" too... Should I just mark the spot where they are planted and wait till the foliage is totally gone before digging? I want to move some of them...

I think marking the spot and digging in September or October would give you better results. Gives them time to mature and get all the energy stored they can. And moving them and transplanting in Sept or October for our zones still gives them time to settle in before winter sets in.

I am in no way an expert on this, but I've had the same experiences you have with moving them and having them rot. The more time the bulbs have to store up energy for next year, the better. Plus, you don't want them to get too much moisture after moving, or that too will cause them to rot.