So with some hesitation, but hope, I purchased some flowers from my local florist and came home with the plan to make a hatchback-garden. I took a bucket, scooped up some rocks from the driveway, filled the bucket with soil, and planted the flowers. Almost immediately the flowers bloomed! A couple weeks later, they're growing insanely fast! I planted some of their sister plants in the yard, and they've barely grown. Which I can't really explain. (Must be Metro magic!)
I might have to try some veggies after my success with this. If I get hungry, I'll just reach back and grab a 'mater. Though my mobile greenhouse of flowers ensures I never have to buy an air-freshener again. This is truly a green car!