I used to do this all the time when I was a kid. I grew all kinds of plants this way. I started out using watermelon seeds because they were easy for a kid to get. You're right about the light. Algae can grow in the nutrient solution if you're not careful. You just have to use a dark container for the roots and nutrient solution. I usually used a 2 liter soda bottle covered in aluminum foil. Back then the soda bottles had a black bowl on the bottom that was perfect for growing plants. I'd cut the top off of the bottle and cover it it foil. The neck of the bottle supported the to plant stem. The roots lived in the black bowl on a paper plate. The dome shaped part was good for covering seedlings until they were big enough to be moved. You could make a terrarium that way too. Now that I'm all grown up I'd probably just use PVC and foam rubber or peet moss to support the stem. I kind of picture a PVC stand with holes sticking out, so that you have a tree with different plants growing from each hole. I saw some PVC fittings that would be perfect for that. You would just circulate the solution from bottom to top with a small pump. Anyway, it's just a thought. On a side note, I saw something called aeroponics at Disney's Epcot Center in Orlando. The plant hangs from a collar of some sort with it's roots exposed to a mist of nutrient solution. The plants move through the mist on a hanging conveyor setup. It was odd looking. Apparently Brussel Sprout roots aren't affected by light much because those plants were HUGE. Sorry to blabber on. I think my ADD kicked in. I love this stuff.