Mermaid Weed (Proserpinaca palustris) Ultimate Care Guide 2022

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Mermaid Weed, which is also known as Saw-Tooth Hygro thanks to the saw-like edges to its leaves, is one of the most dramatic plants in the aquascaping hobby. Not only do the leaves have a stunning natural shape, but they also change from green to deep pink when conditions are right.

Although not the easiest of plants to grow, the rewards for growing this plant are huge as a good specimen of Mermaid Weed makes any aquascape look amazing.

Overview of Mermaid Weed

Mermaid Weed is certainly one of the more challenging stem plants to grow, although not impossible. It is not a plant I would recommend for beginners, but if you have a bit of experience and a good quality aquarium light, it may be a good plant to grow.

The razor-sharp-looking leaves of Mermaid Weed give rise to the plant’s other common name, Saw-Tooth Hygro. Mermaid Weed is a slow-growing plant that typically grows up to around 16″ (40cm) tall.

Mermaid Weed has been grown in the aquarium hobby since the 1960s and has maintained its popularity despite many new plants coming onto the aquascaping scene.

If your location allows it, Mermaid Weed can also be grown in fish ponds outdoors. When grown as a pond plant, the parts of the plant that grow up and out of the water can produce very small, green-white flowers that grow directly on the stem of the plant.

Temple Plant Characteristics

Common Name:Mermaid Weed, Saw-Tooth Hygro
Scientific Name:Proserpinaca palustris
Origins:North America, Central America, Caribbean
Care Level:Moderate
Growth Rate:Slow
Light Level:Medium to High
C02 Level:Low to Medium
Tank Location:Midground or Background
Temperature:62°F – 78°F (16°C – 25.5°C)
Color:Green to pinkish-red
Propagation Method:Cuttings
Maximum Height:16″ (40cm)
Minimum Tank Size:10-gallons (38 liters)

Mermaid Weed Origins

Mermaid Weed grows naturally in many areas of North America, Central America, and the Caribbean. However, due to pollution and habitat destruction, Mermaid Weed is considered to be an ‘at risk’ species and its population is closely monitored, especially in North America.

In the wild, Mermaid Weed prefers to grow in bogs, swamps, marshes, and shallow ponds. When it is found in rivers and streams it tends to be in sluggish to very slow-flowing parts of the stream.

When found in the wild, typically Mermaid Weed will be growing out of the water rather than underwater, and the leaves actually look very different. Mermaid Weed which is growing emersed has much broader, less serrated leaves.

Mermaid Weed General Description

In my opinion, Mermaid Weed is one of the most architecturally interesting plants we can grow in our aquariums. The saw-tooth-like serrations along the edges of all the leaves look stunning in every aquarium I keep it in, and I think you would be hard-pressed to find a setting it didn’t work well in.

Mermaid Weed grows to around 16″ (40cm) tall with bronze to brown stems that are straight, but not rigid.

Although Mermaid Weed is a bright green to golden-green color, when grown under strong lights and supplied with sufficient nutrients, the leaves can turn a pinkish-red color, especially towards the top of the plant.

The closer Mermaid Weed gets to the light, the greater the number of serrations the leaves will develop. Under a really good light, the tips of Mermaid Weed take on a pink, brush-like appearance which is simply stunning.

Ideal Tank Conditions for Mermaid Weed

Although Mermaid Weed is a stem plant, it forms a really robust root structure and the plant draws a lot of its nutrients directly from the substrate. As such, the better the substrate the better Mermaid Weed generally grows.

I currently grow Mermaid Weed in tanks with either Fluval Stratum or regular aquarium gravel which has root tabs buried in it.

I know there are a fair number of hobbyists that like to grow their Mermaid Weed in so-called dirted tanks, which are essentially tanks with a layer of soil underneath the regular substrate. There are a lot of merits to growing Mermaid Weed this way as the plant can draw vast amounts of nutrients directly from the soil. However, it is not a method I employ very often.

As mentioned above, the better light that Mermaid Weed is grown under, the better the plant grows and the more spectacular it will look. As such a good quality aquarium light is a must. I have had some success using the Fluval Aquasky light, but the Fluval Plant 3.0 LED is probably a better bet (see more about this light here).

Mermaid Weed is fairly forgiving when it comes to water parameters. Providing the pH is at least 6.8 and the water temperature is in the region of 62°F to 78°F (16°C to 25.5°C) it will grow happily.

Mermaid Weed is one of those aquarium plants that does not necessarily need CO2 in order to grow but certainly grows faster and stronger with it. I have Mermaid Weed in 3 tanks that run CO2 and 4 that do not. The Mermaid Weed in the tanks with CO2 is a fair bit denser, and the top section of the plants is a lot more pinkish than the ones in the tanks without CO2.

Caring for Mermaid Weed

When I give plant growing and aquascaping talks at fish clubs around the country, I always describe Mermaid Weed as a challenging, but not impossible plant to grow. It doesn’t require a lot of day-to-day care, providing the environment is set up correctly for it.

Mermaid Weed forms a strong, solid root network that it uses to extract nutrients from the substrate.

In my experience, Mermaid Weed is definitely a plant that benefits from the addition of root tabs into the substrate where it is growing. I use a lot of Flourish Root Tabs, which are made by Seachem.

The root tabs deliver nutrients right where the Mermaid Weed wants them.

As with many other stem plants, Mermaid Weed also takes nutrients in through its leaves, so it will benefit from the addition of liquid fertilizer.

Although this plant is a fairly slow grower, in my experience it does benefit from trimming as and when required. I usually have to trim my Mermaid Weed every 6 to 8 weeks, depending on the growth rate.

The good news is those trimming can be grown into new plants if you wanted to (see more on propagation below).

When Mermaid Weed is kept in a tank with CO2 running, it is possible to get it to pearl (release small bubbles of oxygen into the water column). I have never managed to get it to pearl without CO2.

Propagating Mermaid Weed

As with almost every other stem plant in the hobby, Mermaid Weed can be propagated by simply cutting a stem and carefully replanting the freshly cut stem into the substrate. I have found the following steps to work every time for me.

Step 1

When propagating Mermaid Weed, carefully cut a stem just above a leaf or leaves. This will leave a plant in the substrate which will grow strongly from the top, and a freshly cut stem.

Step 2

Carefully push the freshly cut stem into the aquarium substrate, taking care not to crush the stem between your fingers, or damage the cut end as you push it into the substrate.

Step 3

Ensure the freshly planted cutting can not get knocked out of the substrate or float up into the water column. Within 4 to 6 weeks a good root ball should have begun to form.

Step 4

After around 6 weeks you should have a new Mermaid Weed plant that has good root growth. At this point, the new plant can either be left to grow in situ or moved to a new location.

What Fish Can Mermaid Weed be Housed With?

I have found that just about any plant-safe tropical fish can be safely housed with Mermaid Weed. I grow Mermaid Weed in tanks that house Tiger Barbs, Neon Tetras, Angelfish, Bolivian Rams, and German Blue Rams to name a few.

I would not keep any known plant destroyers with Mermaid Weed. Fish such as Oscars, Tin Foil Barbs, Fancy Goldfish, and African Cichlids will all quickly destroy Mermaid Weed.

One species I have always found to work really well with Mermaid Weed are Red Cherry Shrimp. The Red Cherry Shrimp appear to love the texture of the leaves, and I seem to get much higher survival rates when I breed Red Cherry Shrimp in tanks with Mermaid Weed.

Issues with Mermaid Weed

One major issue with Mermaid Weed I have found over the years is that it sometimes drops its leaves or rots off, apparently for no reason. This seems to happen more often when the top section becomes very bushy, possibly because it shades out the lower sections of the plant.

There is a good chance that lack of nutrients can also cause Mermaid Weed to drop its leaves.

I have found that adding additional liquid fertilizer at the first sign of leaves beginning to drop will usually stop the problem before it becomes a major issue.

Where to Buy Mermaid Weed

Mermaid Weed is not a plant that you are going to find in every local fish store. If your local store has a really good plant selection they may well stock it, otherwise, try They typically have a great selection of aquatic plants, and I have always found their service to be excellent.

In Conclusion

Mermaid Weed is a fantastic plant that will make a real impact in any aquarium it is grown in. If you are new to the world of aquatic plants, this may not be the ideal starting point for you, but if you have a little experience under your belt, and a decent aquarium light, I would certainly recommend giving this plant a try.

Mermaid Weed is one of my favorite plants to grow in my fish room.

About the Author

I’ve been keeping, breeding, and showing tropical fish for nearly 30 years. Over that time I’ve done it all! I’ve had great success and I’ve made some really foolish mistakes (like the time I bought an Asain Walking Catfish). Read more…
Richard James

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