How do I make a spearmint plant spread around as ground cover?

There’s a big bare patch in front of my building and I recall how spearmint covered every un-managed spot in a previous garden. And that was a pretty good weed to have, I always enjoyed spearmint & ice-water in the summer.

So I brought home two spearmint plants in 3-inch containers. Is there a good strategy for encouraging these little guys to spread around? Can this be done in a season, or is it a multi-year project?

If you have other ideas for quick & cheap ground cover, I welcome any and all suggestions.