Anna - I can't find my receipt but will ask next time I'm in the store. It's just a mile away.
In any event, if it's hard to find just don't bother thinking about it. Use composted manure.
Cameron - It's a fairly common size for a large pot.
When the second pathetic clematis arrived I was shocked to see it was as bad as the first one. The biggest surprise is that it was double the cost of the one I bought from Garden Crossing. They, and Brushwood, are excellent sources and their plants thrive for me.