Duckweed Care Guide – Planting, Growing, and Propagation

Duckweed is one of the worst and best floating plants in the aquarium hobby. Some people absolutely hate Duckweed with a huge passion because it is a very invasive plant and can be a nuisance.

Nonetheless, it is also one of the most amazing plants, especially for beginners for a couple of different reasons. For example, Duckweed is so hardy that it can thrive in a wide variety of tank setups. Basically, it does not care much about water parameters at all. Because of its fast growth, it also consumes a lot of ammonia and nitrates in the tank making our water cleaner, etc.

Just like other floating plants commonly used in the hobby, Duckweed forms dense mats or colonies which stay afloat on the water surface and provides shade to tank inhabitants, as well as performing a whole host of other functions.

Keep on reading for everything you need to know about Duckweed including background information, a detailed care guide for this plant species, in addition to other essential information pertaining to its usage in aquariums.

Duckweed – check out the price on Amazon

Quick Notes about Duckweed

Common Name	Duckweed
Scientific Name	Lemnoideae
Difficulty	Easy
Lighting	Medium to high
Optimal pH	6.5 – 7.5
Water hardness	Soft to hard (does not matter)
Optimal Temperature	15 – 32 C (60 – 90 F)
Substrate	Not needed
Growth Rate	Very Fast
Placement in Tank	Floating
Size	Up to 0.3 inches (or 8 mm)
Fertilizers	Not needed to low
CO2	Not needed
Propagation	Division
Color	Light green to dark green

Note: The most popular theory (why it is named that way) says that it is from the fact that Duckweed is eagerly consumed and distributed around the world by ducks. Duckweed sticks to their feathers and remains viable even when it is dry, while ducks are flying from one place to another.

Origin of Duckweed

Duckweeds are very small, free-floating aquatic plants from the family – Araceae. Also known as Bayroot, Water lentils, or Water lenses, they are among the smallest of flowering plants.

This plant family was first described in 1821 by J.E Gray. Duckweeds were once regarded as a subfamily of the Araceae under the name Lemnoideae by A. Engler in one of his publications on aroids. This was later changed when he recognized duckweeds as a separate independent family – Lemnaceae.

There are 5 known genera of Duckweeds and they are: Spirodela, Landoltia, Lemna, Wolffiella, and Wolffia.

More than 40 species of Duckweed exists, with 9 species occurring in North America. Common Duckweed (Lemna minor) is the most widespread species and has a subcosmopolitan distribution, ranging across Canada and the United States of America, Southeast Asia, and Europe.

The taxonomical status of Duckweed is summarised below:

Kingdom: Plantae
Order: Alismatales
Family: Araceae
Subfamily: Lemnaceae

Habitat of Duckweed

Duckweed grows in freshwater ponds and slow-moving streams in virtually all the continents of the world except Antarctica; ranging from the tropical to temperate regions.

The plant spreads rapidly across quiet bodies or water that are rich in nutrients, it grows best in areas where annual daytime temperatures range between 60 – 90 °F (15 – 32 °C).

Also, when the aquatic ecosystem dries out or declining temperatures occur, Duckweeds possess adaptive mechanisms to persist until conditions that can support growth return. This occurs through late summer flowering or the production of starch-filled structures or turions which are denser than the fronds so the plants sink to the bottom of the water body and become embedded in dried mud.

Description of Duckweed

These vibrant green plants have a simple oval structure, and they lack an obvious stem or leaves. The greater part of each plant is a small organized “thalllus” or “frond” structure, 1 – 8 mm (0,04 – 0.3 inches) long and 0.6 – 5mm broad.

The fronds can attach to one another and look like an extensive mat or blanket while on the surface of water bodies, giving it a lush green appearance that stands out.

Roots in both Spirodela and Lemna are adventitious. The size of the roots ranges from a few millimeters up to 15cm deep, and they plunge into the water column to help stabilize the plant and absorb essential nutrients.

Duckweed reproduces both vegetatively and sexually; vegetatively by asexual budding or division and sexually by flowering, although this is rare. The fruits contain several ribbed seeds which are capable of going into dormancy and will germinate under favorable conditions.

Tank Requirements and Water Parameters

Duckweed is among the smallest flowering plants, this plant is hardy, undemanding, and suitable for a variety of tanks which includes low-tech, and high-tech planted tanks. Some species of Duckweed can thrive even in low saline waters e.g. For example, Lemna minor can tolerate between 0.5 and 2.5 present sodium chloride levels while others prefer life in freshwater habitats.

Tank size:

Duckweed can be grown anywhere, including a 1-gallon tank (~4 L). It is a good choice for nano aquariums.

Water type, Temperature, Hardness, and pH:

Water temperature: Duckweeds grow optimally in water temperatures between 15 and 32 °C (60 – 90 F). Above or below that range, Duckweed just sort of sits there and does not grow.

pH: Duckweed survives at pH between 5.0 and 9.0 but grows best at a pH range of 6.5 – 7.5.

Hardness: In general, Duckweed does not care about hardness. It can easily tolerate soft or hard water. Nonetheless, for optimal growth and development of this plant species, maintain water hardness in the range of 2 – 15 GH, 1 – 12 KH.

Lighting:

This plant grows naturally in open ponds with very little shade; direct sunlight does best for this plant. However, that is not really suitable for aquariums housing other plant and animal species that may not appreciate direct sunlight or a very powerful artificial high light.

At this point, full-spectrum artificial LED lighting will suffice, you are required to provide medium – high lighting for this plant in order to allow it photosynthesize and grow better. Incandescent bulbs are not recommended, as they give off a great deal of energy as heat which can overheat the plant and the tank water.

Substrate:

Duckweed is a floating plant and as such, there is no specific substrate requirements for it. This plant will perform well in a healthy tank full of essential nutrients necessary for its optimal growth and development.

Water flow:

In the natural ecosystem, Duckweed inhabits ponds and shallow streams where the current is slow-moving. They often do not survive in fast-moving water (<0.3 m/sec). Therefore, still / slow water currents are recommended for tanks housing this plant.

CO2 and fertilizer application:

This plant does not require CO2 dosing, it gets it from the air. However, if you want to increase Duckweed growth, fertilizers (NPK- Nitrogen, Phosphorus, and Potassium) or supplements should be provided on a regular basis.

Important: If you keep shrimp in the tank with the Duckweed, I would highly recommend reading my articles:

CO2 in a Planted Tank Guide
How Copper Affects Dwarf Shrimp
Shrimp Safe Plant Fertilizers
The point is that Copper (most fertilizers contain copper) is extremely dangerous to the shrimp.

Planting and Propagation of Duckweed

Planting duckweed is not a hard task. Just like other floating plants, you can grow Duckweed in aquariums by simply placing the plants on the water surface, also dose it with essential nutrients to aid acclimatization and promote healthy growth.

Duckweed is perennial, and this implies that it will live for more than 2 years in the presence of optimum growth conditions. It is an adventitious plant that reproduces asexually by vegetative propagation. They can also carry out sexual reproduction because they are flowering plants, however, I would not worry about this way of reproduction.

Interesting fact: Duckweed has the smallest flower in the world, however, you will not see it without magnifying glass.

In the aquarium hobby, Duckweed mainly reproduces by cloning. The plant grows and divides asexually, almost like a single-celled organism does.

When Duckweed matures, it starts creating new buds in the center of the frond. In its turn, these buds transform into new fronds while still attached to the parent frond.

Note: Depending on the species, daughter fronds are produced alternatively and in a pattern from two pockets on each side of the mature frond in Spirodela and Lemna. In Wolffiella and Wolffia only one pocket exits. These fronds possess veins and are composed of chlorenchymatous cells separated by large intracellular spaces that are filled with air (aerenchyma); this allows it to float on the water column.

Once they are fully mature, they separate from the parent and immediately start producing their own copies. This way of reproduction allows Duckweed to have an extremely fast rate of growth. This plant needs only 16 hours to double in biomass. That is why Duckweed is capable of covering an aquarium in next to no time.

Note: Some studies say that every plant can produce around 10 copies before death.

Care and Maintenance of Duckweed

The good thing about this plant is that it is easy to grow and requires no special care. Beginners will totally love this one.

The plant grows fast under optimal water conditions, so it should be properly monitored. Also, a reasonable quantity should be scooped out when it appears like it is covering up the whole water surface.

If you have a hang on the back filter with strong flow, Duckweed will be pushed around the tank by the current. It will slow down its growth. Therefore, it will be better to redirect the current flow 4 – 5 inches (10 – 12 cm) below the water surface. It will also help to avoid the tiny plant particles from clogging or getting trapped in the filter.

Another solution to this problem is to create a “roped off area” for the plants by using clear air tubing strung across the top of the aquarium. In addition, you could also place a few extra pieces of sponge at the very front where water exits. It will slow the flow as well.

Duckweed appreciates nutrient-rich water, therefore, regular supply of nutrients- essential fertilizers and supplements should be encouraged.

Moderate – high lighting conditions (preferably high light) and very slow water currents should be provided as well to support the healthy growth of this plant.

Problems associated with Duckweed

Fast growth: Duckweed is characterized by an explosive growth rate; it grows and reproduces rapidly once the nutrient levels are high. In most cases, you may witness the overgrowth of Duckweed in the aquarium. It can cover the entire surface and may be difficult to control.

Light penetration: Duckweed stays afloat of the water surface and will form dense colonies or mats which might block light from reaching submerged aquatic plants in the tank.

Oxygen depletion: If you do not have any aeration in the tank or there is no water flow that can disturb the surface – Do not let it create a thick layer on the surface for a long time. It can result in oxygen depletion in the water column that can lead to the suffocation of your fish or shrimp.

Turn yellow: If your Duckweed turns yellow, it can be a nutrient deficiency or a lack of lighting. For example, it can survive with a moderate amount of ambient lighting. However, if it’s combined with low nutrient levels in the water column, then it can be a problem.

Difficult to get rid of: Once Duckweed settles in the tank, it can be extremely hard to remove (unless you have plant-eating fish like Goldfish, etc.). This is not the plant that you can scoop with the net and forget about it. Oh, no! It will be back again and again and again… until you give up. So, think twice before introducing it to the tank.

Sticky: Duckweed can stick like glue to any surface (hands, hose, net, plants, filter, glass, any type of decoration, etc.).

You can also read “How to Spot Nutrient Deficiencies in Aquatic Plants”.

Benefits of Duckweed

Aesthetics: The lush green foliage of this plant provides a natural outlook in the tank which mimics that of ponds; Duckweed covers the top layer of the aquarium and adorns it beautifully.

Filtration: Duckweed performs water filtration by effectively absorbing phosphates, nitrates, ammonia, and toxins in the tank. Actually, it is probably the most efficient nitrate-sucker plant. It improves water quality by preventing the accumulation of harmful chemicals.

Algae control: This plant helps to effectively reduce the growth of algae. Duckweed shades out algae, thereby killing it entirely or in some cases, diminishes the number of algae cells, and the amount of dissolved oxygen that algae can produce in the water column.

Shelter / Cover: Some fish species and fry, use this plant as shelter. In addition, other aquatic species; both fauna and flora dwelling in the aquarium, will appreciate the shade provided by Duckweed. Without any doubt, shrimp will love Duckweed.

Light penetration: I have mentioned it as a problem before but it can also be a good way to filter lights if you have plants that do not need it (for example Java Fern, Amazon Sword, Marimo Moss Ball, Anubias, etc.).

For more information, read the article “Top 10 Low Light Aquarium Plants. Pros and Cons”.

Prevents fish jumping: Once Duckweed covers the surface, it will keep fish from jumping, when you do not have a lid.

Indicator of the toxins: Very bright green color often means that the Duckweed absorbs a lot of nutrients. Therefore, there might be some problems with water quality. The darker color of the plant usually means that water does not contain extra-bad stuff.

In addition, check out the length of the roots. As nutrient levels in their water drop, Duckweed’s roots quickly elongate to compensate for the shortage of nutrients.

Duckweed as Fish and Shrimp Food

This plant is quite high in protein. According to the study, Duckweed species have an average of 37.0% of crude protein, therefore, it can be used as a food source for fish, shrimp, snails, crayfish, crabs, etc. You will be surprised to know how fast your livestock will consume it.

Note: Use a blender to mix it up with montmorillonite clay that acts as a binder. Spread it thinly over the surface and let it completely dry. Break it in small pieces and feed your fish or shrimp. They will like it!

How to Control or Get Rid of Duckweed

First of all, be patient because you will not remove it in one day.

Turn off your filters and aeration while you are removing it. Otherwise, it will be pushed around your tank.
Scoop it from the water surface.
Check every surface in the tank including the rim of the glass and filter. Shake up other plants. Duckweed can be absolutely everywhere, even underwater! Actually, it can survive for a long time underwater. So, even if you skip one of them, it will come back as an army in no time.
Repeat the next day.

Do not use the same equipment (nets, tweezers, siphon hose, etc.) between your tanks or you will get Duckweed in all of your tanks!

Note: If your tank setup allows, it is possible to control Duckweed by reducing light and increasing water flow. Duckweed prefers sunlight to grow and will hardly, survive in the shadow.

Interesting facts about Duckweed:

Duckweed is used in genetic and biomedical research.
It functions as a bioremediator by removing heavy metals like lead, arsenic, cadmium, copper, zinc amongst others from water, they are regarded as water purifiers.
Duckweed is being studied by researchers around the world as a possible source of clean energy. Rutgers University and North Carolina State University have ongoing projects to determine whether Duckweed might be a source of cost-effective, clean, renewable energy.
This plant plays a key role in the conservation of water since a cover of Duckweed will significantly reduce evaporation.
Duckweed has a high-protein content and it is considered as a significant potential food source in some parts of Southeast Asia. It contains more protein than soybeans.
Common Duckweed can be utilized as a food supplement in broiler diets and also as fodder for ducks.
Duckweed can be transported across regions by migrating birds, wind, or water current.

Duckweed and Tankmates

It is very easy to keep Duckweed with:

Fish (like Guppy, Molly, Swordtail, Loaches (Clown loach, Coolie loach), Discus, Platies, Tetras, Zebra Danio, Otocinclus Catfish, etc.)
Shrimp (Red Cherry Shrimp, Blue Velvet Shrimp, Snowball shrimp, Crystal Red Shrimp, Caridina cf. babaulti, Blue Tiger Shrimp, Malawa shrimp, Blue Bolt shrimp, Amano shrimp, Ghost shrimp, Bamboo shrimp, Vampire shrimp, etc.). Basically, you can keep any shrimp species with it. They will love to hang from the Duckweed and eat.
Snails (for example, Ramshorn snails, Nerite snails, Malaysian Trumpet snails, Japanese trapdoor snails, Mystery snails, etc.).

As we can see, Duckweed is compatible with most plant and animal species that prefer low lighting. However, some snail species and herbivorous fish like Plecos, Goldfish, Cichlids, Rosy barbs, Sliver dollars, and Tilapia are likely to feed on this plant.

In abundance, Duckweed can serve as a meal for species that love to eat them. Therefore, it is not a bad idea since they grow and multiply very quickly. On the other hand, most carnivorous fish species will not touch it.

Floating plants like Duckweed will be a good choice for crab and crayfish tanks.

Buying Duckweed

Duckweed is readily available in offline pet stores and can also be purchased online from reputable aquarium vendors as well. A cup of this plant is inexpensive; it costs $10 or less and can contain up to 200 pods.

Duckweed can be easily damaged due to its delicate nature, therefore, you should handle it with care. When buying this plant, ensure that the roots and fronds are in good condition, absent of discoloration, brown or yellow spots.

Quarantine Duckweed

Unless you are completely sure that the plant is safe, for example, it was grown in sterile/laboratory conditions (in vitro) and in vitro pot is not damaged or opened, do not forget to quarantine and disinfect Duckweed first with bleach or potassium permanganate to avoid the risk of contamination.

The plant can have parasites, pests like snails, or even predators (dragonfly, damsefly nymphs, etc.).
It could also be treated with chemicals (pesticide) to remove parasites, snails, etc. However, these chemicals are extremely poisonous to fish, shrimp, and other invertebrates.

To find out more, read my articles:

How to Remove Snails from a Shrimp Tank.
How to Quarantine and Disinfect Aquarium Plants.
Pesticides in Shrimp Tanks. Plants Quarantine.

In Conclusion

Although some people hate Duckweed and declare war against it, it does not mean that this is a bad plant after all.

Duckweed is a multiple functional plant and a good choice for beginners in the hobby; it is a floating plant, and as such, it doesn’t need a specific substrate requirement to grow and reproduce.

This plant is undemanding as regards to maintenance, it requires minimal care which mainly involves provision of nutrients and reduction of the plant mass to avoid clouding the water surface completely.

If you are in search of a small, fast-growing, and undemanding plant, I would like to let you know that Duckweed ticks all the boxes.