BJ: I agree with Apple, space them 3 feet apart if you have the room.
If you don't, you could be daring like my uncle was. He dug out an are about 6 feet around and planted his Lathams in the center. Now, about 10 years later, he has a huge "Thicket" as he calls it about 20" around in his back yard and about 10' high. They just keep propogating throught the roots.
I started 3 years ago with 6 plants, 3 lathams and 3 heritage and I put them all in one row, about 2 feet apart. Now I have 4 rows and each plant is a couple of inces apart. They propogate fast ad you can dig up the new shoots ad start new rows.
Good luck and have fun.