1-gallon (trade gallon) or about that size nursery pots. I prefer injection-molded pots or thermoformed/co-extruded/euro pots, but I could also use the old standard blow-mold type pots if they are in good condition (they deteriorate more quickly in sunlight, when left out).
I got a few this spring, but am using almost all of those to plant stuff for this swap.
