What is the correct type of soil mixture to use for figs in pots?  I have a Lattarula that I would like to keep potted - outside in summer, in my cool garage in winter. 

I have it potted now - it's done OK in terms of looking green and aliive - but fruiting and growth were minimal this year.  I previously had it in the ground but it tended to die back severely where I had it.  It would recover each spring but I got few fruits.  I think Lattarula fruits mainly on the previous season's wood so dieback was a problem for fruit production.

I am in Zone 7a, northern Delaware.

If you plan on keeping it in a pot for a few seasons, a good recommendation would be 1/3 pine bark mulch or peat, 1/3 perlite or equivalent, 1/3 crushed granite or pea stone and some lime. This should give you a good draining soil that will last for 2 seasons when you should root prune or re-pot. I've also used a simple 1/2 potting soil and 1/2 perlite but after a season re-potting is needed. Best of luck.