How do I change the primary site on my multi site network?

I, like many developed my site one step at a time; starting with a single wordpress site, then adding some sub-sites, then a multisite network and now pro sites and domain mapping. I have that working, I think. Just a few more things to figure out before I go live.

My original site is my own garden site. It is currently the primary site on my network. I would really like that site to just be about gardening and selling plants, but now I have it all mucked up with the network. I would really like this to be a network of garden and foodie blogs…so I would like the main site to be a kind of directory, not my garden site. The directory site might be named something like catrinasgardensites. I wouldn’t mind purchasing another domain name for it. How should I go about this? I’m kinda hoping you won’t say I have to start from scratch.