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Floating Gardens and Soda Bottles
Sixth Graders Build Better Bottles
“After exploring soil and basic chemistry with my sixth grade team, we talk about plant needs,” reports Los Angeles, CA, teacher W. Alden Wright. Even in this urban school, it’s common knowledge that plants and soil go hand in hand. “So when I tell the students that, well, we’re not going to use dirt, they are absolutely disbelieving,” explains Alden. Water power, he tells them, will be the name of their game.
Alden launched his hydroponics unit with a bit of history, teaching students that the Aztecs designed some of the earliest hydroponics systems out of necessity. “In an effort to protect their food from enemies, they built mud-covered floating rafts for growing crops,” says Alden. Determined to create models of these floating farms, student groups loosely lashed twigs together to form mini-rafts, topped them with soil, water, and grass seed, then floated them in “ponds” made from plastic trays or lined cardboard boxes.
Simple Soda Bottle Systems
Once their raft gardens sprouted, students prepared to create individual hydroponic setups by gathering clear 2-liter soda bottles, then selecting seeds to grow. (Despite contrary wisdom that light inhibits root growth, the Alden has discovered that plants actually grew better in clear bottles than in colored ones.) “I told students they could choose any two salad vegetables,” says Alden. Lettuce, anaheim chiles, cherry tomatoes, nasturtiums, and basil were among the selections. Each student started 4 seeds in each of two 1- by 1-inch cubes of rockwool. “As the seedlings grew, I had students cull all but one in each cube, and required them to justify their choices,” says Alden. When seedlings were a few inches tall, students transplanted them to their soda bottle setups.
“My team teacher (who is also my wife) and I spent a day with our 60 students building the planters,” says Alden. “Our objective is to keep it simple. Our cost is just 9 ½ cents per unit.” Here are the nuts and bolts of their setups: After cutting off the top 1/3 to 1/2 of the bottle, drill a 1/4-inch hole in the cap. Meanwhile, cut a 1- by 10-inch strip of dress interfacing, which will draw the water/nutrient solution up from the bottom reservoir to the plant roots. Next, invert the top section and set it in the bottom half. Feed the wick up from the bottom reservoir, through the bottle cap, and into the inverted top. Fill in around the wick in the top with perlite. When the seedling in rockwool is ready to be moved to the setup, continue the wick in an “s” shape into the bottom of the rockwool, then fill around and just above the cube with perlite.
“I usually work in a chemistry lesson by having students build their own fertilizer from a variety of minerals and we sometimes experiment with ratios,” says Alden. “It’s amazing how quickly you can see results in hydroponic systems.” That done, I then tell them that we can simply use Schultz plant food.” Students are responsible for deciding when to change the nutrient solution, or when to simply add more water and nutrients to what’s there. When they change the solution, many try a low-tech effort to provide oxygen to plant roots: blowing bubbles through a straw! (See the Simple Straw Aeration setup described in this guide.)
“We’ve had great luck raising most salad vegetables in these setups under fluorescent lights, except for celery and carrots,” says Alden. In fact, the class had cherry tomatoes that climbed up the wall all the way to the ceiling on netting. As the plants grew and bore fruit, students keep daily growth logs on plants, which also include drawings. “One student had drawn his pictures in the same corner of each page in his journal, and has he flipped through the pages one day, discovered that his plant seemed to grow!”
“Food is such a puzzle for these urban kids,” says Alden. “You know, the chocolate milk from the brown cow sort of thing. But kids get so excited about caring for from something from seed to stomach and knowing they can grow their own food; and they do take the concepts home with them.” One student, he explains, even made a hydroponics setup for his apartment bedroom window. “As long as it’s fun for me, I’m sure it will be fun for them,” he says. “And I love how much we learn from the kids.”