Seems to me that they can be aggressive. I'm pretty new to hardy geraniums, but from what I've read, there are varieties that have a tendency to be aggressive. Some more so than others. So, I guess it depends on whether you like them enough to pull out the extras.

Here is a link that might be useful: Aggressive Geranium info

We have 18 or 19 different perennial geraniums in our garden and only one prolific self seeder. That is G. pyrenaicum. It is, however easy to pull up or to move to where you want it. Here is a picture from last summer showing mostly G. pyrenaicum album, but with one blossom of the more usual pink. Perhaps it is our exposed Zone 2 climate that keeps the others under control.
Leo

Here is a link that might be useful:

In my garden I find G. phaeum to self sow in an aggressive way, and G. macrorrhizum to spread laterally, but not really aggressively. G. macrorrhizum also self sows fairly freely.

I was able to get into the garden yesterday after a week of rain and would add G. praetense to the list of vigorous self-seeders. I would strongly recommend that if the pink geranium you have is G. pyrenaicum that you get rid of it now if you don't want it everywhere. From a distance I thought I had a bad invasion of chickweed but when I got into the garden I found it was G. pyrenaicum absolutly everywhere.

Thanks for the info. I went to the site ChlorophyllJill noted. That writer doesn't see spreading as a problem - to each his own! I enjoyed your picture Leo - the 3 colours of flowers look wonderful against all that green. I think I will dig up the pinks and stick with the white and the blue for now. I have found a lot of babies between the stones in my walkway. I have a hard time throwing plants out but I think it's the best thing to do. I stuck one pink in a pot - a friend has no garden, only a deck and we're going to see if it survives for her over the summer in a pot on her deck.

Thanks again. cnid

what about the woodland geranium? does it spread well
thanks much

Do you mean Geranium sylvaticum, Karen?
It doesn't actually self sow in my garden, but the clump does increase, and it can be fairly easily divided in the spring, if you want more specimen.