Duckweed is the smallest of aquatic flowering plants, notes Iowa State University. Duckweed reproduces by budding and will cover the entire surface of a pond if left to grow on its own. Small quantities of duckweed feed fish and other aquatic wildlife, but a large amount of duckweed will cover the surface of a pond, reducing oxygen levels and blocking out light. When growing duckweed for feed, the crop must be contained to reduce damage to the ecosystem.
Collect duckweed seed from surrounding pond areas. Collecting duckweed from local ponds ensures the duckweed is adapted to the local area, says the World Bank.
Place a bamboo divide in a fresh water pond to reduce the spread of duckweed from wind. Duckweed is highly invasive, notes Iowa State University, and will spread readily if left to grow.
Add the duckweed seed to the containment area in a place with partial sunlight. Add the duckweed seed at a rate 21 to 32 oz for each 10 square feet (600 to 900g per square meter) for best results.
Check on the duckweed seed after a week. Do not add fertilizer as the duckweed will recover and begin growing around this time.
Collect duckweed with a fine mesh net screen.