I've got two videos for you this morning — both show you how to make a bag garden. The first is a a short animated video that just gives you the basic instructions. The second shows a very impressive, articulate Ugandan young woman creating a bag garden with the help of her family and friends. Both videos are associated with the charity Send a Cow that gives direct, practical help to poor farmers in East Africa.
This is a great project for those with a small space because everything grows vertically. I would think you'd be able to do this on a balcony. It would also be a fabulous project for kids, either as a family or with a school group. I've already forwarded this information on to the teacher at my boys' school who is in charge of their environmental club.
You should be able to purchase all the materials you need for the bag garden locally, but the Send a Cow website also offers bag garden starter kids. It's a U.K. site, but they take credit cards so as long as they ship to the U.S., you should be able to order from them.
You don't need to see this second video to be able to understand how to build a bag garden, but if you have the time, I encourage you to watch it and see a real one being created.