My costume was a Homemade Chia Pet Costume (or a Chia Head.)
I started by simply painting my face orange and wearing an orange shirt. This was to be the Terra-Cotta part. Then I got Wheat Grass at the health food store for the part growing out of my head. I gave it a crew cut. I sliced the bottom half an inch off the soil to eliminate some of the weight.
I put the grass and soil in a clear disposable container and wrapped the container in an orange ribbon. I wove another orange ribbon through the container and tied it under my chin. It is a somewhat hard costume to wear since the container slides around on your head. I am sure other ideas could work. Perhaps growing real grass seed coming out of a nylon stocking would work better.
You could even use this idea to go as a carrot, or even a flowerpot with plants. The way to make the costume special is to use real turf though, not artificial grass. You will win a prize for the most original costume!