It turns out to be possible to grow an entire farm on a 3-inch deep window sill. Spotted at Uncommon Goods:
Above: The Micro Greens Kit comes with seeds to grow organic red cabbage, mini carrots, and tom thumb peas. It's $40 from Uncommon Goods.
Above: The kit comes in a box made of recycled steel, and includes enough soilless growing medium and seeds for two full crops.
For more ideas for space-challenged edible gardens, see 5 Quick Fixes: Grow Herbs on Your Windowsill.
N.B.: This is an update of a post originally published on June 8, 2012.