Posted: 27/05/2012 at 06:07
Here's a snap of my hardy geraniums, taken last Summer. This is a border alongside a lawn. I never have to do any weeding in it. The plant is so vigourous that it encroaches on the lawn, and will easily smother the grass. I keep it in bounds by strimming it...
I have some other varieties of hardy geranium that are not as vigourous, and not as successful.
Kate mentions campanula. I have some campanula, and for me, this is a long way from effective ground cover. That's partly due to my soil, campanula is not rampant im my garden. I find that campanula can become infested with grass, and grass is very hard to remove from it.
Dove mentions lamium. Many people consider lamium to be an invasive weed. It's a pretty weed. I can believe that lamium might be very successful.
Alina mentioned ajuga. I don't actually have any of that. But I can believe that could be very successful too.
Alchemilla is worth a try too.
There's a very close boundary between 'invasive weed' and effective ground cover.
You could try a few plants of each, and see which one romps away. One of them would come to dominate the others, depending on your soil and conditions.