How to Build an Onion Pond

Place the polystyrene over the top of your aquarium. Cut the polystyrene with a utility knife so it will fit into the aquarium tightly. The piece should have some free play and be able to freely float upward or downward as the water level changes. The polystyrene will float above the nutrient solution in the aquarium and hold the onions in place.

Cut out three holes evenly spaced in the polystyrene to hold the plastic cups for the onions. If you are using an aquarium larger than 20 gallons, you can cut more holes for more plant cups. Be sure the cups will fit tightly into the holes. Onion roots rot easily so the cups will protect the plants from too much moisture.

Cut four 1/8-inch holes into the bottom of each cup with the tip of the utility knife. Add the perlite into the bottom one-third of each plastic cup. Perlite is a common growing medium for hydroponics.

Place the air stone at the bottom of the aquarium. Insert the aquarium tubing into the air stone. Connect it to the aquarium pump that will be stationed outside the aquarium. These materials are all readily available at pet stores where they sell fish supplies.

Fill the aquarium with water and add the hydroponics nutrient solution. Follow the manufacturer's instructions. Place the polystyrene on top of the water with the nutrient solution. The polystyrene should just be touching the water.

Place the young onion plants into the perlite in the plastic cups. Place the plastic cups into the holes on the polystyrene. Turn on your grow lighting and be sure the aquarium pump is on.