I have mine in the garden, which is almost pure clay, with some manure mixed in for fertilizer. They're already 2 feet across, more or less. They do like root space, and I think the garden soil will work fine. I did have 10, but down to 5, since I kept them too wet, so i wouldn't do the peat/sand idea. I hope ya have a deck or something, since they sure stink, and I probably wouldn't bring them inside unless it got unusually cold!( Which never happens in June anyway.) Good luck!
Aslan