Lots!
I counted the number of containers I had out last Summer, I'll have to think or go out when I can and count them. I have more in the garage (lots of 16", 14" and 12").
I've been using 24", 20" and 16" and I have 3 very large black pots that nurseries use for large trees. Size does matter when it comes to plants.
I even bought another 24" and a 20" pot that I didn't get around in 2012 that is waiting to be added to the bunch I use for 2013.
One year, when I was using smaller pots (12" and up), I had 70 pots outside! I had them up and down on the front steps, on the driveway, on the patio and on the front porch. That was the only year. I usually have the pots on the front porch, the patio, the driveway and a section in the backyard that has concrete pavers to set the pots on.
I have a 20" pot in a flowerbed to use for my 'Major Wheeler' Honeysuckle. I have a tall metal trellis leaning to the pot. I did it because I was concerned the rabbits would eat the honeysuckle plant to the ground and kill it.
