This is my first year growing potatoes and the plants have grown so large they are taking over the garden. Can they be topped or pinched back to stop the growth?
Huge potato plants is nothing to worry about -- unless they are 100% above-ground. Don't forget to "mound" or "hill" up your potato plants when they get to be about a foot high. You really shouldn't cut them back at all but it wouldn't hurt to trim down the very outer leaves and smallest stems. These articles will give you some good additional information on growing potatoes: