Hi! I live in MN zone 4 and have a similiar path. I've started planting Irish moss between the stone slabs. It gets a cute little white flower and seems to be winter hardy. I haven't had as much luck with the Scottish moss which looks similiar. Mine gets a light amount of foot traffic and doesn't seem to be the worst for the wear. Good luck!

hostaheaven - Where did you get your moss? I'm in your zone/state, so if you bought locally and were pleased, I'd love to know. I'm dry-laying an irregular bluestone patio this weekend and am thinking that I'd like to grow something between the stones. I'll bring in black dirt but hadn't yet started looking around for what to plant.

I've gotten the Irish Moss at three different places; 1. The Friends School Plant sale, 2. Rush Creek Gardens over in Wisconsin, and 3. Bachman's. If you call around I'm sure you'll find it. Good luck building your patio this weekend!

I just planted a lot of the Irish and Scottish moss in my pathway (same as yours) and it's all died, too much shade. If your path doesn't get full sun, try something else and save the money I just lost.
Treeskate, I tried the mulch approach, but even after packing it down, the rain eventually washed it out. I put some crushed gravel down. I don't like it, I wish I had put down something finer, like sharp sand. But it discourages weeds and doesn't wash away. To kill weeds, I bought a gallon of Roundup, with a sprayer that shoots a thin stream, not a spray. I can target one weed at a time, without overspray.