Growing Potatoes in Bags

I don't think you need a specialized bag so long as it's big enough. You can simply cut a drainage hole at the bottom. A 40 gallon trash bag will do just fine. Just use a rich organic compost. I'd go with one potato plant per bag to get nice size spuds.

I've used empty compost bags in the past. roll the top down at least more than half of the bag and fill 1/3 with compost. Plant your chitted potatoes a couple of inches below the surface. when the stems are about 6" tall add some more compost, roll out some of the bag. keep repeating throughout the year.
I've used 70litre+ bags with 3 or 4 chits in. Obviously you have make sure you water then sufficiently.

Of course--empty compost bags are the answer. Why didn't I think of that! Thank you so much!
I grew just one bag of potatoes last year and was delighted with the result, much better than when I had sown them in the vegetable bed.