The Complete Mermaid Weed Care Guide

mermaid weed

Plants go a little under the radar when people are designing an aquarium. Most aquarists know the benefits that plants offer to fish, so add some without giving it much thought.

Mermaid Weed is a beautiful plant that gives many fish a run for their money. It boasts plenty of color and its leaves are very distinctive, allowing this plant to stand out against others.

What makes this species even better is its hardy nature. It is very easy to care for, anyone can give it a go without hitting problems if they have done their research.

Anyone thinking about buying this wonderful freshwater plant has come to the right place.

We will talk you through everything you need to know about Mermaid Weed, from how to design your aquarium to propagating it.

Mermaid Weed Facts & Overview

Mermaid Weed Care Guide

Care Level:Easy
Color Form:Green and red
Origin:North America and Central America
Height:Up to 16 inches
Minimum Tank Size:10 gallons
Tank Set-Up:Freshwater
Growth Rate:Slow

Mermaid weed (also known as Saw-Tooth Hygro) is a freshwater aquatic plant in the Haloragaceae family, also known as the watermilfoil family. Its scientific name is Proserpinaca plustris.

The species is naturally found in North America, Central America, and the Caribbean. It lives in warm areas where there are marshes or wetlands.

It first became popular for aquariums in the 1950s.

There are actually many varieties of Mermaid Weed. They can vary in appearance, but they share the same requirements, so it doesn’t matter which one you end up with.

These are very tough plants. They can tolerate a range of conditions and should survive if there are small changes in their environment. This makes them great for a beginner starting their first aquarium.

Mermaid Weed is a commonly used species for ponds and paludariums too.

Always check that any plants you intend to buy are healthy. Look out for signs that the plant is struggling, such as fading colors or damaged leaves.

You should be able to buy a few stems for $5 or so. If you want some more without having to pay extra, you could try propagating it. This will take time though.

Mermaid Weed is an attractive plant. It is a brilliant way to provide some shelter for your fish or improve the oxygen content of the water.


Mermaid Weed can vary in appearance because it is grown in many varieties. Its color and shape are different depending on where it is grown.

The plant is characterized by serrated edges to its leaves in the wild. This creates a saw-toothed aesthetic. They aren’t sharp, but it helps to deter animals from nibbling and causing damage.

The leaves can be more needle-like in captivity.

When the leaves grow out of the water, they are more blade-like.

Mermaid Weed is typically green with reddish hues on display towards the top. The red only emerges if there is enough lighting to meet the plant’s needs, so it’s a good sign that the plant is healthy.

If left to its own devices, Mermaid Weed could reach a maximum size of 16 inches tall and 6 inches wide. This takes up a lot of space, but you can trim it down to the size you want.

As a tall species, it is best suited as a background plant where it can extend up into the water column without blocking the view of everything else in the tank.

Healthy stems of Mermaid Weed can be beautiful. They are a great way to add color to your setup.

Habitat and Tank Conditions

Mermaid Weed Care Guide

You would naturally find Mermaid Weed in North America, Central America, and the Caribbean. It is thriving in areas like Connecticut, New Hampshire, Rhode Island, and Vermont.

It prefers slow-moving bodies of water in marshes and wetlands, like ditches, lakes, rivers, streams, and ponds. It can grow very densely.

Their water conditions can vary quite a bit, which is useful when designing an aquarium. They usually live in warmer water with an acidic pH.

Recreate this natural environment at home to maintain a strong and healthy plant.

Tank Conditions

A fine, sandy substrate is recommended for planting your Mermaid Weed in. This is softer than coarse gravels and less likely to damage the roots.

In a pond, you could use sand or clay. Using weight as an anchor helps to keep it submerged.

You are free to design the rest of your setup around the needs of other inhabitants, like fish. The only things you need to bear in mind are the water conditions.

The temperature can be anywhere from 50°F to 82°F, which shows how tolerant the species is. Similarly, pH can range from 5.0 to 7.5.

Mermaid Weed needs medium-strong lighting to stay healthy. Most standard aquarium lights are sufficient.

Fertilizers aren’t necessary, but some people suggest injecting CO2 into the tank. This helps to speed up the growth rate (which is useful for propagation) and maintain strong colors.

What Size Aquarium does it need?

Mermaid Weed can grow quite tall, but you can keep it in small aquariums, it will just need extra care and more regular trimming.

A 10-gallon tank is a minimum, but a larger one would make your life easier.


Mermaid Weed Care Guide

Growing this plant shouldn’t be much of a struggle. It’s a species that anyone can try; its needs are simple, and it doesn’t take too much work to maintain it.

A clean tank is important for the health of anything you want to care for. Partial water changes and clearing away excess algae are the main jobs that need doing.

We have already described the broad range of conditions that Mermaid Weed can survive in, so it is easy to set up a suitable tank for them.

Maintaining the water conditions is important though. Sudden changes to the water parameters could be fatal.

Use a water testing kit each week to make sure that the water parameters are at the levels they should be. You can then respond quickly if they’re not.

Mermaid Weed is a slow-growing plant, so it is easy to keep it from getting out of control.

If it ever gets larger than you would like, trim the sides of the top. You can choose to dispose of these trimmings or replant them to propagate your Mermaid Weed.

When disposing of trimmings, either bury them, dissolve them in bleach, or add them to compost. Anything else and you could spread this species to your local area.

Nutrient supplements help to improve plant growth. They are not required most of the time, but they can help if the plant is looking unhealthy. CO2 injections will help in the same way too.

Tank Mates

Mermaid Weed is commonly kept in a community aquarium surrounded by living things.

Fish can be great tank mates, do your research before buying some. Most species aren’t an issue, they will just use Mermaid Weed as shelter and ignore it the rest of the time.

Other species can cause quite a lot of damage to your plants. Mermaid Weed can tolerate some light nibbling from fish, but it may not survive being uprooted by species like Oscars.

Most common invertebrates, like shrimps and snails, are fine too. Crayfish and Freshwater Crabs are not suitable as they are very destructive to plants.

You can mix Mermaid Weed with other plant species. This is a good way to add interest to different areas of the tank. Just don’t force your plants to compete by planting them too densely.


Propagating Mermaid Weed is easy. They do this naturally using side shoots, but you can intervene and speed up the process.

Mermaid Weed produces side shoots that develop roots and leaves of their own, eventually separating and forming a whole new plant.

You can trim these side shoots once leaves have developed and they are a few inches long. You are then free to replant them wherever you want in the tank.

Mermaid Weed grows slowly, so it may take a while to propagate. The process will speed up exponentially as more and more stems are produced.

Nutrient fertilizers and CO2 injections can help to speed up the growth rate a bit.

Is Mermaid Weed Suitable for Your Aquarium?

Chances are that this plant is an excellent option for you. It can be cared for by anyone since it is won’t of the most resilient plants around.

Mermaid Weed is easy to care for, easy to propagate, and easy to design an aquarium for because its needs are very broad.

This is a very attractive plant that will mix both reds and greens into your setup. Its serrated/needle-like leaves stand out compared to other plants.

It proves that plants can be interesting, just like fish.

There really are very few reasons why you shouldn’t add Mermaid Weed to your aquarium, paludarium, or pond.

Is Mermaid Weed one of your favorite aquatic plant species? Let us know why in the comments below…

About Robert 468 Articles
Robert Woods is the creator of FishKeeping World, a third-generation fish keeper, and a graduate in animal welfare and behavior. He is also a proud member of the Association of Zoos and Aquariums, the Marine Aquarium Societies of North America, and the Nature Conservancy.

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