How to Grow Duckweed in Aquaponics

Place a plastic tank below the elevation of the hydroponic grow beds and above the elevation of the fish tank. Maximum growth rates are achieved in full sun, but duckweed will grow steadily with a half day of sun.

Drill a 3/4-inch hole 1 inch below the top of the plastic tank with a hole saw.

Slide the threaded end of a bulkhead fitting through the hole so the rubber gasket rests against the inside wall of the tank. Thread the nut onto the bulkhead fitting and tighten it with a pair of channel lock pliers. The bulkhead fitting creates a watertight seal so the water used to grow duckweed can drain out and return to the aquaponics system.

Run 3/4-inch PVC pipe from the bulkhead fitting to the fish tank. Use PVC primer and cement on all fittings and configure the piping to slope continuously down to the fish tank, so the water can drain by gravity as it overflows from the duckweed tank.

Place the outlet of the pump tubing that returns water from the hydroponic beds to the fish tank into the duckweed tank. The goal is to modify the aquaponics system with the addition of a duckweed tank that makes use of the water from the grow beds on its way back to the fish tank. When the pump is activated to drain the grow beds, the duckweed tank will be filled and the water will overflow into the fish tank through the bulkhead fitting. In this way, the same water level will be maintained inside the duckweed tank.

Place the duckweed into its tank. After it has grown to cover the surface of the water, a portion of it can be harvested on a daily basis to feed to the fish.

Monitor the system to make sure the growing conditions for duckweed are met. If it is grown inside a greenhouse, provide ventilation or shading to keep the water temperature below 91 degrees Fahrenheit for optimum growth rates. In outdoor systems, the duckweed will go dormant once temperatures drop below freezing, but will re-emerge in spring.