Full Instructions with Pictures on how to make a cheap greenhouse out of PVC pipe and plastic for less than $15!
DIY Worm Tower For Your Garden : drill lots of holes in a pvc pipe. Bury all but 6 inches in garden. Place kitchen scraps in the hole. Worms will come in and eat and then transfer the "goodies" throughout the garden.
Great Diy Idea for GreenHouse
Vertical Garden Using Plastic Milk Bottles. This would be a great thing to do at school - maybe give each child a couple of seeds and see what grows?