Duckweed – Plant Profile, Care Guide, Tank Setup and How to Grow

Duckweed might be one of the most controversial plants in the aquarium world, and a lot of aquarists have a love-hate relationship with it.

It’s considered by many to be a rampant pest, but it has several benefits and can contribute to the stability of your aquarium’s ecosystem.

In a controlled quantity, it can provide nutrients and act as a water purifier. If left alone, it can be an aggressive invader, spreading rapidly and covering your aquarium’s surface. This leaves your fish and other aquarium plants with compromised oxygen and sunlight levels.

Despite this, it can be very beneficial to an aquarium’s ecosystem, which is why it’s commonly added to tanks. Duckweed care is also very straightforward. It’s the ideal low-maintenance plant and perfect for beginners in the world of planted tanks.

A carpet of duckweed covering a waters surface
Liz Sullivan [CC BY-SA 4.0], via Wikimedia Commons
If you’re considering growing duckweed, or merely searching for a good overview of the plant’s profile and some interesting facts, you’re in the right place.

In this article, I have gathered all the information you need to get you started with duckweed. We have a summarised table of facts and figures, followed y a complete buying and care guide, ending with tankmate compatibility and a few interesting.

Overview and Statistics

Here is some summarized general information on this plants profile and care that you might find useful.

CharacteristicDetails
Common name(s):Duckweed, bayroot, or water lens.
Scientific Name(s):Lemnoideae
Family:Lemnaceae within the Araceae family.
Origin:Native to Europe, Asia, Africa, and North America. Found mainly in subtropical or tropical areas.
Color Form:Light green.
Maximum Size:Each ‘pod’ is 0.8 inches long.
Growth Rate:Exponential in ideal conditions.
Care Level:Easy.
Water Conditions:Quiet and nutrient-rich water, pH 5.0-9.0, 42.8-91.4°F.
Lighting:High
Minimum Tank Size:2 gallons. As long as you have an inch of water in your aquarium, you’ll be able to grow duckweed.
Supplements:Fertilizers such as manure or mineral supplements.
Placement:Floating or just below the surface.
Propagation:Very fast division.
Tank mates / Compatibility:Carnivorous fish. Herbivores will eat the plant.

It was originally used by local farmers to feed ducks and fish, and quickly became popular, creating a flourishing market.

At least 40 species of duckweed are known, including nine which can be found in North America alone. Lemna minor—spread out across Canada and most of the United States—is one of the most common species.

Because of its minuscule size, it’s difficult to distinguish between the different species. The stem size and the number of roots usually help with identifying the variants.

It’s ideal for those of us who can hardly keep a plant alive because it can survive extreme temperatures and climates. In fact, it can be found everywhere except in deserts and frozen climates. It thrives best in still waters containing decaying organic matter; this provides duckweed with all the nutrients it needs.

While many aquarium owners are looking for ways to remove it from their aquariums, other well-informed enthusiasts see the value of adding it to their tank ecosystem.

What Does Duckweed Look Like?

It’s only a few cells thick and has a very simple oval structure. It contains two “air pockets,” allowing it to float or remain just below the water’s surface.

The roots are usually short, although they can vary from less than an inch to about 5.5 inches deep, stabilizing the plant and helping it obtain the needed nutrients. It is bright, light green in color.

It’s also one of the smallest flowering water plants, producing small fruits, each fruit containing up to five seeds. The seeds will sink to the bottom of the pond or tank and, because they’re resistant to drying, can wait until the most suitable time to flourish.

Where to Place Duckweed in a Tank

As mentioned above, it is a floating plant and lays on or just below the water’s surface. A small floating PVC tube—connected at the ends in a ring shape—can be used to contain the plant within a limited area.

Some aquarium owners successfully grow it on rings placed inside the aquarium. However, this needs special care and attention.

What Benefits Can it Bring to Your Aquarium

Through a process called bioremediation, duckweed is a natural water purifier and helps treat contaminated water by absorbing excess nitrogen and phosphates. Research has shown that it can also be used to capture toxins and odors, controlling the development of algae in your aquarium.

By covering the surface with a thick layer of greenery, duckweed acts like a blanket. It prevents mosquitoes from laying their eggs, and reduces water evaporation—which can be very beneficial in hot and humid climates.

Some fish species, such as bluegills, use it as a shelter where they find refuge. Your tank’s inhabitants, along with any low-light plants you have, will appreciate the shaded areas provided by this plant.

Due to its high protein content, it can be used as a food source for fish, such as goldfish and tilapia. It helps biomass growth when nutrient concentrations fall below needed levels. It can also help reduce the growth of some light-loving algae species.

Preferred Habitat

It’s able to adapt and survive in extremely adverse conditions. However, it does still have preferences and limits. Let’s take a look at those now.

Minimum Size Tank Required

Because it requires nutrient-rich waters and needs minimal depth to survive, it will grow best in shallow waters, or an aquarium with a maximum depth of 20 inches.

Water Conditions

Duckweed thrives where water is almost completely still; it won’t survive in fast-moving waters with a current.

Although most varieties can only survive in fresh water, some can live in low saline waters as well. Lemna minor, for instance, can tolerate between 0.5 and 2.5 percent sodium chloride levels.

It can survive when water temperatures range between 42.8 and 91.4 degrees Fahrenheit. However, the growth will slow when the temperature drops below 68 degrees or reaches 86 degrees. Although it survives pH levels between 5.0 and 9.0, it grows best within the 6.5 to 7.5 range.

In case the water temperature drops too low, it can sink to the bottom of a lagoon, pond or aquarium, but will come back to life when the water temperature increases.

Lighting Requirement

Because it naturally grows in open ponds with very little shade, direct sunlight is usually preferred.

If you have a small tank, however, direct sunlight might cause the water to overheat and evaporate faster. It’s important to replace the lost water regularly, in this case.

Duckweed can also grow in indirect sunlight, but will do so at a slower rate. If a window isn’t available, artificial LED lighting for planted tanks can be used, hanging 12 to 20 inches above the tank. Incandescent light bulbs aren’t recommended, as they use a large amount of infrared energy, overheating the plant.

Substrate Requirements

There are no set substrate requirements, as it is a floating plant. That said, a healthy tank full of nutrients will help it to do well.

In order to maintain a nutrient-rich ecosystem at home, lower-level ground plants should be added to the aquarium, and mineral supplements regularly used.

Exponential Growth Rate

Because it is a low-maintenance plant, and you shouldn’t have any issue keeping it alive. It reproduces so rapidly that, in ideal conditions, its surface area size can double in just 16 hours!

Depending on the environment, it can become several inches thick on the surface and, before you know it, take over your tank. In just 60 days, duckweed can grow enough to cover a 30-hectare area!

This plants growth has to be monitored very closely as it can easily clog your water filter. If the growth becomes uncontrollable, it might also cause oxygen and light deprivation, harming your fish and other water plants in your tank.

Because it sticks to everything it touches, once you’ve introduced it into your aquarium, you’ll find it is practically impossible to remove.

In this fascinating video you can watch a time-lapse of duckweed self-propagating:

How to Care for Duckweed

No special care is required, it’s actually harder to get it out of your tank than to grow it!

Because it is so fast-growing, it’s important to monitor it daily, and if it takes more than half of your tank’s surface, scoop it out. It can be frozen—for up to three months—to be used at a later time.

Try keeping your water filter four inches below the water’s surface, as the tiny plant particles can easily get trapped in the filter.

To support its growth, it requires a supply of nutrients. If needed, fertilizers or supplements can be added to your aquarium on a weekly basis.

For optimum growth, ensure that your tank is positioned under direct sunlight and that the water surface is completely stagnant. Even the slightest current will slow down growth significantly.

If your duckweed is turning white, it’s struggling. The water and environment should be checked and reviewed.

Buying Advice

You’ll find it readily available in pet stores, specialist aquarium retailers, garden centers, and can also be bought online. Although it grows all over the world, it’s best to buy a strain that’s native to your home country for a better chance of adaptability.

This plant is inexpensive, and a small cup of live duckweed can be purchased for less than $10. Because it reproduces very quickly, it’s usually packaged in small quantities.

Whether you’re buying from a garden center or online, it’s sold as a live plant most of the time. The actual seeds are extremely rare, and their minuscule size makes them difficult to spot and harvest.

It is very delicate and can be easily damaged. When buying, ensure that the roots and leaves are in good condition, without brown or yellow dots.

It’s also sensitive to cold and frost, so it might not survive shipment during winter.

Once you have your new duckweed, simply place it inside your tank and let it float freely. It might need some time to adjust but, with proper care, it should quickly flourish, adding beautiful shades of bright green to your aquarium.

You can also find it in most wild ponds and natural bodies of water. Here’s how to harvest some:

  1. Fill a small container with water and duckweed from the pond.
  2. Cover the container to prevent splashing while bringing your treasure home.
  3. Because of its fast growth rate, 50 to 100 pods will be enough.

Adding It to Your Tank

Ready to get this fast growing floating plant into your aquarium? Here’s how to go about it:

If Taken From Mother Nature

  1. To avoid risk of contamination, make sure to disinfect your duckweed with bleach or potassium permanganate—one teaspoon per 11 gallons of water—before placing the plant into your tank. If not disinfected, it could introduce parasites or snails into your aquarium’s ecosystem. These chemicals can be easily purchased at your local pharmacy and will kill any potential parasites.
  2. Soak for 30 seconds.
  3. Place the prepared duckweed on the surface and let it float freely. Always place a small amount of it in your tank first, as a tester.

If Taken From Your Garden Center

  1. Place your freshly bought duckweed in a 12–14-inch tray.
  2. Fill the tray with tap water or freshwater from a nearby pond.
  3. Make sure that the plant gets about 10 hours of sunlight daily, ideally from direct sunlight.
  4. A few times per day, check the tray and remove any damaged plants.
  5. After a week, replace the water.
  6. Within ten days, it will start to multiply and grow. It can then be placed in your aquarium.

Tank Mates and Compatibility

It is compatible with most other common flora and fauna species found in aquariums.

Avoid These Fish

Because they’re packed with nutrients and protein, fish tend to love duckweed. Herbivorous fish will eat it.

If you’re trying to actively grow it, it might be better to stay away from cichlids, goldfish, Ameca splendens, tilapia, and common plecos.

Suitable for These Fish

Carnivorous fish, on the other hand, will let your duckweed thrive. They’ll also appreciate the cooling shade this plant provides by covering some of the surafce.

Avoid These Plants

In the plant kingdom, duckweed and algae are natural competitors. Some algae species (red-colored, blue-green algae and dinoflagellates) can produce toxins which threaten duckweed’s survival.

Also, any plants you have rooted at the bottom of the tank in the substrate might not be happy to have it hogging all the sunlight. Otherwise, it is compatible with most fellow tank plants.

Propagation and Reproduction

It is a perennial plant and will live for over two years. Its reproduction doesn’t require any intervention as, under the right conditions, it reproduces prolifically on its own.

It’s an adventitious plant that reproduces and divides asexually, cloning itself repeatedly, just like single-celled organisms. When they mature, the cloned cells break off, forming a new plant. In a warm environment and within two weeks, one parent can produce up to 17,500 plants!

Duckweed’s small flowers, although pretty, don’t play any role in its reproduction.

These plants will reproduce and multiply much faster in direct sunlight. It’s best to place your aquarium under a window so that it receives at least 10 hours of sunlight daily.

Herbicide Control

It’s rapid growth can be scary to some. However, options exist that will help you regain control over your rampant plant.

This is unlikely to happen in a controlled environment such as your fish tank. But if you’ve planted duckweed in an outdoor pond and it’s taken over, the following info might be useful.

The following active ingredients have shown success in eradicating out-of-control duckweed:

  • Carfentrazone
  • Fluridone: This herbicide ingredient tends to work slower than contact herbicide.
  • Flumioxazin: This active ingredient is most effective when applied to young growing plants in water with a pH lower than 8.5.
  • Diquat
  • Penoxsulam: A low dose of this herbicide will be highly efficient. As a plus, it was shown to have no adverse effects on most animal species.

Before using any herbicide, make sure you get expert advice. This is especially important if you’ve never used harsh chemical substances before.

Interesting Facts

  • It seems to be the smallest flowering floating plant in existence.
  • It is used in genetic and biochemical research.
  • The plant contains more protein than soybeans and is sometimes cited as a significant potential food source. It’s eaten as a vegetable in some parts of Southeast Asia and some report that it tastes similar to sweet cabbage.
  • It attracts and concentrates heavy metals (in particular cadmium) and can indicate water pollution levels. This is something to consider if consuming duckweed as food.
  • It is on the red list of endangered species in Switzerland.
  • Rutgers University and North Carolina State University are currently investigating if duckweed can be a source of cost-effective, clean, and renewable energy. Not only is it considered a carbon-neutral energy source, but it could also help remove carbon dioxide from the atmosphere.
  • Because it’s so tiny, it can be easily transported from one body of water to another by animals and birds.

Summary

Duckweed is very easy to grow and maintain, so it makes an ideal water plant for beginners. You will need to keep a close eye on its expansion rate though. Left untended, it has the potential to spread over the entire aquarium’s surface and jam up the water filter.

Overall, it helps you to maintain a balanced environment and keep all life in the tank happy. It makes a fresh and healthy snack for your fish and provides shade to other aquatic plants down below. If you’re looking to add some greens to your tank,  it might be a good option to consider.

Are you planning to grow duckweed? Have you successfully integrated the plant into your fish tank? Please let us know in the comment section below.

Happy fish keeping!

B Hamilton

Hey there! I'm Brian, a lifelong enthusiast and fish keeper with a wealth of knowledge and experience on freshwater aquariums, that I love to share on this site. If you have any questions or need any help, please do ask in the comments section below, I'd love to hear from you and will help where I can.

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