Wash and dry the potato.
Cut off the top one-third of the potato. Scoop out the cut end with a melon baller to a depth of about 1 inch.
Fill the scooped-out area with potting soil. Sprinkle grass seeds onto the soil. Press the seeds down lightly and cover them with a thin layer of soil. Moisten the soil with an eyedropper.
Roll a stick of modeling clay into a ball. Press the ball against the table to form a flat base, and mold it into a small conical "mountain" resembling a volcano. Make a 2-inch-wide hole in the top of the cone with your knuckles. Press the round end of the potato into this hole. Push the clay securely around the potato’s perimeter to hold it upright.
Draw eyes, ears, a nose and a mouth on a sheet of craft foam. Cut the facial features out and glue them to the potato with tacky glue. Give the glue at least an hour to dry.
Place the potato head in a location that gets moderate sun. Water the grass seed once a day. After about a week, the potato head should begin to sprout “hair.”