My friend is willing to give me some of her seed potatoes. Can I grow them well in a 3 gallon pot?
No. In the right conditions in a big container you can get 5-8 times as much by weight as you plant. You could not plant more than one seed potato in a three gallon pot, so you'd be lucky to get enough potatoes for one serving. You'd be better off planting in a 30-gallon trash bag like the other recent post in this forum discusses. Potatoes, like their cousins tomatoes, are very big plants that require a lot of room.
The smallest container I ever tried them in was 10 gallons. The returns was ok, not great but ok for the work involved. I have heard of folks trying a 5 gallon bucket but the production was minimal. You'd get potatoes, just not many of them and they would be small.
Have researched growing potatoes?
If not, It's my understanding that the stem needs to be covered as it grows, so it will need a fairly large container.
I am going to try this season, with an old squirrel cage from a cooler.
The stems only need to be covered to protect any spuds growing near the surface from getting exposed to light. That's it. Mulching would do the same thing.
I have read of people growing them on top of the ground and kind of want to try. Just separating them from the dirt with newspaper. Keeping them covered with hay. I've read about it in a couple of places. They are very easy to harvest then just pick up the hay and collect the potatoes.
Here is a link that might be useful: One method
Here is another method.
Growing in a plastic bag.
Here is a link that might be useful: http://www.diynetwork.com/how-to/how-to-grow-potatoes-in-a-trash-bag/index.html