>> I can carry pieces of potato in a plastic grocery bag, walk along the string line and drop them through a 3 ft piece of plastic pipe so they land in the right place, then pat them down with my foot, and take another step.
The plastic pipe is a great idea!
Maybe tucking the grocery bag through your belt, or tying one handle to some string that goes over your shoulder will free up one hand.
Mary, perhaps even leaning left and right, or balancing on foot, causes some strain on your sutures. Using a hoe as a cane to steady yourself may take some strain away from your torso and upper legs. You could tie or tape the pipe to the hoe handle, to make both a one-hand-tool.
Maybe you could use the hoe to tamp down the soil, instead of one foot, if indeed that pampers your surgery at all.
SOME movement keeps you in shape after surgery, but I believe that the earliest healing goes faster when there is almost no pulling or stretching. Take care of yourself, and when you see the doc again, he or she will smile instead of frown.