What Causes Duckweed?

Duckweed can be problematic for many pond owners because it is highly prolific. Here are some steps you can take to reduce the spread of this aquatic weed.

What is duckweed?

Duckweed is a plant that floats on water. It is a tiny, green, leafy plant similar in shape and texture to a lily pad. Occasionally the plant will flower and produce the world's smallest flower. The individual plants are usually no larger than 5 mm, yet it can quickly take over any body of standing water. By blocking out the sun and eliminating photosynthesis, duckweed will cut off new growth in a pond and destroy not only a food source in plants, but a pond's vital oxygen source as well. Over time, if duckweed develops to this level, the pond will become completely stagnant. Duckweed originates from seeds dropped from birds migrating from pond to pond; the seeds settle to the bottom of the water becoming dormant until they can reproduce. Duckweed seeds or fronds will flower to reproduce and until optimum conditions are reached, pond silt and mineral deposits will protect fronds on the bottom of the pond.

Prevention

While it is difficult to completely prevent duckweed due to the fact that it is spread from pond to pond by birds and animals, chemical tests which can indicate whether conditions for reproduction are optimal. If high levels of nitrogen and phosphorus are present, then the water is nutrient-rich enough for the duckweed to develop. Changing the chemical composition of the water to reduce nitrogen and phosphorus can help to prevent the weed. Over-the-counter chemical compounds can assist with restoring the pond's chemical levels to a normalcy.

Nutrient Reduction

There are two major ways to eliminate duckweed in a pond's ecosystem: nutrient reduction and aeration. In nutrient reduction, you eliminate the accumulation of fall leaves, field run-off, and other debris that drains into the pond and The balance of the pond will eventually level out naturally, but it can sometimes take several years to clear all the sediments from the pond.

Aeration

Aeration is a process that uses a compressor to blow air throughout the pond to its deepest parts, similar to how a fish tank is oxygenated. By constantly circulating the excess sediments caused by decay and run-off, the ecosystem in the pond will eventually recover and the newly formed food chain will start to create new life using the duckweed as a food source. However, this method can also take a few seasons to take effect.

Considerations

Duckweed growth is a natural process, so it is unlikely it can ever be completely prevented; however, it can be controlled using the methods described above. The difficulty in removing this tenacious plant will be entirely dependent on the quantity of the duckweed, along with the amount of sediment still deposited on the bottom of the pond water.

Resources

• general information for quality pond care