Root Depth and Pot Size
I'm not sure if I remember this correctly, but I think some kinds of basil need, or at least like, a loooot of soil to spread their roots in (the summer, small-leaf kind?) and other ones don't, i.e. they do fine in confined soil. I just put in a bunch of basil pots and have both the wide-leaf and a couple tiny-leaf varieties. Does anyone remember which is which?