I have planted lemons and tangerines and lost the marking for each. After 3 years of plant development, they look pretty sturdy but have not made much. One of them made 1 flower last year. I am not sure they are all tangerines, but they definitely seem so. I would like some advice on pruning and fertilizing for a productive container life or whether there is any way they would be happy in zone 6 USA outside.

Thank you or your help!

Image link: