More to explore:
Milk Jug Garden ( a great kids project)
Milk jug garden
milk jug garden
DIY Vertical Pallet Garden
I've seen this done with milk jugs as well...
Craft Your Own Vertical Pallet Garden
Dump A Day Fun Uses For Old Milk Jugs - 20 Pics
DIY upside-down tomato planter, with milk jug, chopstick & water bottle!
Vertical gardening, with a wooden pallet.