Frogbit Roots – What They Are, and How To Manage Them

Charlie Morton

Charlie Morton


Frogbit Roots

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Amazon Frogbit is an attractive floating plant often grown in tropical freshwater aquariums. Its modest demands and many useful attributes have made it a popular plant among fish keepers for decades.

This Amazonian plant isn’t entirely without its problems, however. Its fast growth rate and ability to cast heavy shade over the aquarium means that it usually requires some management to keep it in check.

In this guide, you’ll discover the pros and cons of growing Amazon Frogbit, as well as everything you need to know about managing this prolific plant.

What Is Amazon Frogbit?

Amazon Frogbit (Limnobium laevigatum) is a floating aquatic plant from South America that is popular in aquariums around the world.

Also known as the Smooth frogbit, or South American sponge plant, its broad, floating leaves make it useful for providing shade in the aquarium, and the long, thread-like roots make an excellent shelter plant for small fish underneath.

In the wild Amazon Frogbit grows in slow-moving rivers, lakes, and swamps in the same habitats as neon tetra, angelfish, and discus.

Sadly, the plant has also escaped from aquaculture and become invasive in parts of North America, Africa, Asia, and Australia.

In Which Conditions Does Amazon Frogbit Like To Grow?

Minimum recommended aquarium size20 Gallons
Care levelEasy
Temperature70-85 °F

Amazon Frogbit is fairly flexible when it comes to water conditions. It can grow at temperatures anywhere between 70-85 Fahrenheit, with a pH range of anywhere between 6.0 – 7.5.

This makes it suitable for almost all freshwater tropical aquariums, so long as the tank is at least 20 gallons in size.

As with many floater plants, Amazon Frogbit won’t appreciate a fast water current, since this can cause its roots to break up. Try to divert the flow from your power filter away from the plant or use an alternative such as a sponge filter that doesn’t create much current.

Since it is a floating plant, Amazon Frogbit can obtain much of its CO2 from the air and so doesn’t require CO2 injection to thrive. It may in some cases, however, need to be fed with fertilizer.

Does Amazon Frogbit Need Fertilizer?

Whether or not Amazon Frogbit requires fertilizer supplements to be added to water depends on the particular growing environment. In tanks that already have plenty of nitrates, phosphates, and essential minerals in the water, they’re unlikely to need feeding.

But in tanks with nitrate levels below 5 ppm (parts per million), some extra feeding could be necessary. Slow growth rate and small, pale leaves are signs of inadequate nutrition.

The easiest way to test your water for nitrate levels is with a complete test kit, such as the API Master Kit.

How Big Does Amazon Frogbit get?

In normal aquarium conditions, each leaf on mature plants grows to around 1 inch in diameter, but high nutrient levels could make the leaves grow larger.

The roots of Amazon Frogbit are famous for growing very long indeed! In the wild, the roots of mature plants can reach a whopping 2 feet long, but in aquariums, they’re more likely to be between 5-15 inches, depending on the water conditions and height of the tank.

How Fast Does Amazon Frogbit grow?

Given the right water conditions, Amazon Frogbit can grow at an impressive rate – in fact, some people have said it grows ‘like a weed’!

When the plant is happy, it can produce two new leaves on each stem every two days. The long, thread-like roots also grow very fast and can make significant progress in a single week.

Because of its fast growth, some aquarists avoid Amazon Frogbit, saying it will ‘take over the tank’ too quickly.

The floating leaves can indeed cast a lot of shade to the water underneath, and the roots, if not managed, can turn into a massive matrix that crowds out space for fish to swim and other plants to grow.

Other aquarium owners, however, simply like to prune the roots and stems to keep them under control.

Can I Prune Amazon Frogbit Stems?

Pruning Amazon Frogbit leaves and stems is indeed possible, and in many situations, it may be necessary!

With a pair of sharp scissors or garden secateurs, you can cut back any stems that are growing further than you’d like them to. Try to cut stems back to just above the leaf clusters so that you don’t have leftover pieces of stem rotting afterward.

Can I Prune Amazon Frogbit Roots?

Yes, and it might be a good idea to prune Amazon Frogbit roots often! The roots of the frogbit plant are notorious for hanging down like vast tentacles and consuming a lot of water space.

While some aquarium owners and fish will enjoy the jungle-like effect of this dense network of roots, others will, understandably, prefer some more free-swimming space for their fish and a lighter, more open appearance to the fish tank.

Frogbit roots can be cut back to 2-3 inches with a pair of sharp scissors or garden secateurs and maintained at this length every 1-3 weeks depending on the growth rate of the plant.

Interestingly, some aquarists have observed Frogbit roots growing faster when nitrate levels are lower in the aquarium. This is probably due to the plant searching for nutrients by sending its roots deeper down into the water.

This phenomenon must have its limitations, however, since all parts of a plant require some source of nitrogen to grow.

Compatible Fish Species For Amazon Frogbit

Amazon Frogbit is an especially useful plant for fish that enjoy subdued lighting or a shady environment.

The shadows cast by the broad leaves can create a beautiful dappled light effect that fish species such as betta fish, angelfish, catfish, and loaches will find more comfortable than being constantly exposed to the bright aquarium bulbs overhead.

As long as Amazon Frogbit is kept under control, it can be a useful plant for most types of fish species except those that are notorious for destroying plants such as Oscars, African cichlids, and goldfish.

Fish that prefer to swim in large expanses of open water such as danios and rasboras may also find this plant a little stifling if it’s allowed to occupy large portions of their swimming space.

Amazon Frogbit In Breeding Tanks

Floating plants like Amazon Frogbit are crucial for species of fish that build bubble nests such as gouramis, Siamese fighting fish, and paradise fish.

Without floating plants to support their nest, these foam nests will often get dispersed or carried away by the water current, effectively preventing the fish from breeding successfully.

Floating plants with long roots are also very useful to add to breeding tanks where young fry need a refuge.

Fish fry naturally enjoy congregating in the safety of the dense roots underneath floating plants, and by adding them you’ll be contributing to creating a healthy, natural setting for your baby fish to grow up in.

Frogbit Roots

Why Is My Amazon Frogbit Growing So Slowly?

In densely planted tanks, there might simply not be enough nutrients to go around to all of the plants, causing them to grow slowly.

Check nitrate and nutrient levels using test kits and apply liquid fertilizers if necessary.

Frogbit plants might also be growing slowly if your aquarium lighting isn’t strong enough – although this would be a rare occurrence for a floater plant that has direct access to the light.

Any normal fluorescent or LED lights recommended for your tank size should suffice.

One final reason that your frogbit could be growing slowly is if your fish and invertebrates are eating it when you’re not looking!

Fish such as Silver Dollars, Mollies, and Headstanders, as well as pest snails, are especially fond of chewing down plant material which can make the growing progress of your plants much slower than those that are undisturbed.

In some instances, this free pruning service performed by your fish may be welcome, so long as it doesn’t get out of hand!

Why Is My Amazon Frogbit Dying?

In most situations, Amazon Frogbit will thrive and grow quickly. If it’s growing slowly and you don’t improve conditions it might begin to die.

Test your water and make sure that nutrient levels and pH levels are sufficient.

Another reason that your Frogbit could be melting or rotting is when the leaves are positioned too low in the water. If you submerge the leaves in the water, they might struggle to surface properly again, causing the plant to rot.

Therefore always make sure that leaves are placed above the water’s surface.

Does Amazon Frogbit Help To Clean Aquarium Water?

Scientific research has shown that Amazon Frogbit is a good candidate for phytoremediation – the cleaning of contaminants such as heavy metals from the water.

In the aquarium, it also does a good job of absorbing excessive levels of nitrates and phosphates that might otherwise cause algae blooms or adversely affect the health of your fish.

Does Amazon Frogbit Deplete Oxygen Levels in an Aquarium?

One of the biggest potential drawbacks of growing Amazon Frogbit is that in large masses it can deplete oxygen levels in the water.

Although this plant photosynthesizes like any other plant, drawing in carbon dioxide and expiring oxygen, most of the oxygen released by Amazon Frogbit goes out through the leaves and into the air above, rather than down into the water.

The lower light levels available to plants growing below Amazon Frogbit will also reduce their rate of photosynthesis and oxygen production.

All of this can lead to a lower oxygen environment for your fish, which can create problems.

Fish that need highly oxygenated water such as Hillstream Loaches, White Cloud Mountain Minnows, and Flying Fox Fish, as well as freshwater shrimps, may suffer badly or even die from hypoxia (dissolved oxygen depletion) in such conditions.

To prevent low oxygen levels from becoming a problem, prune your Amazon Frogbit regularly to allow light to penetrate down to submerged plants in the aquarium, and consider adding an additional oxygen source such as an air stone or bubble bar.

How To Propagate Amazon Frogbit

Amazon Frogbit is incredibly easy to multiply.

Simply detach or cut away any portion of the plant, place it in warm water with plenty of light and adequate nutrients and it will begin growing away rapidly.

Even pieces of broken stems with leaves attached will usually sprout new roots when kept in warm, well-lit water.

Where You Can Buy Amazon Frogbit

Amazon Frogbit is widely available from both local pet stores and online outlets. Because the plant is so easy to propagate, it’s incredibly cheap to buy.

Often sold in bundles, each piece will typically cost less than a dollar.


Amazon Frogbit is a beautiful and vigorous floating plant that has the potential to become a weed, both in aquariums and in local water sources.

With the right management, however, it can be a very useful plant in a fish tank, creating a sheltered environment and an attractive dappled shade effect that many fish and fish fry will love.

To discover more fascinating floating plant options in your aquarium, head over to our specially dedicated page here.

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