Pearlweed or Hemianthus micranthemoides is a popular, versatile aquatic plant species for decorating freshwater aquaria.
This bright green stem plant is renowned for its ease of care, low maintenance, adaptability, and versatility. Pearlweed can be grown as a foreground, mid-ground, and background plant depending on the look you are aiming for in your aquascape.
Keep reading for everything there is to know about the Pearlweed, and how to plant and care for it successfully in freshwater tanks.
Quick Notes about Pearlweed
|Other Names||HM, Baby tears, Pearl weed, Manatee mudflower,
Amano pearl grass and Pearl grass
|Scientific Name||Hemianthus micranthemoides or Hemiánthus glomerátus (conflicting taxonomy)|
|Tank Size (minimum)||5 gallons (~20 liters)|
|Lighting||Moderate to high|
|Optimal pH||6.5 – 7.5|
|Water hardness||Soft to hard water (1 – 20)|
|Temperature||19 – 28 °C (66 – 82 °F)|
|Substrate||Any (can float)|
|Growth Rate||Moderate to fast|
|Placement in Tank||Foreground / midground / background|
|CO2||Not needed but recommended|
|Propagation||By clipping mature stems|
Origin of Pearlweed and Potential Misidentification
Hemianthus micranthemoides, otherwise known as Pearlweed is a well-known aquarium plant that belongs to the family Scrophulariaceae and genus Hemianthus — of which member species are referred to as pearl weeds.
Hemianthus micranthemoides is often mistaken for Hemianthus callitrichoides, so it is not unusual to see traders mix it up. However, Hemianthus micranthemoides can be distinguished from Hemianthus callitrichoides as the latter has much smaller foliage than the former.
In addition, many biologists suppose that Hemianthus micranthemoides was to be extinct in its native range since 1941.
So, the species discovered to be growing abundantly in still waters, wet pools, and ditches in Florida is actually Hemianthus glomeratus and not Hemianthus micranthemoides.
At the same time, there is also a popular belief that Hemianthus micranthemoides are still much available in the aquarium trade due to their cultivation and preservation in nurseries and gardens.
Currently, it is not possible to clearly identify Pearlweed. Further research should be made to properly classify this plant.
Habitat of Pearlweed
Pearlweed is native to the Mid-Atlantic region of the United States; growing in tidal rivers; preferably in areas with enough water movement and gravel/sandy based substrates.
Description of Pearlweed
Pearlweed is a bright green, low-growing stem plant that is suited for adorning different sections of a large, medium, or even nano tank.
This plant has small, ovate, narrow, bright green leaves (1 cm or 0.4 inches in length) that grow oppositely, in whorls of 3-4; forming attractive vegetation on the aquascape.
The species also has delicate, thin green stems that grow upright in low lighting, and in contrast, forms dense mats under intense lighting conditions.
Also, the leaves produce oxygen bubbles from their surface as a result of optimal photosynthesis aided by CO2 supplementation and ample light levels.
Tank Requirements and Water Parameters
This plant can be grown in a variety of tanks; including a nano tank with a volume of 5 gallons (~20 liters), but it will require frequent trimmings.
Thus, it’s best to cultivate Pearlweed in a tank of at least 10 gallons (~40 liters), however, keep in mind that the plant will fill your tank easily under optimal conditions.
Water type, Temperature, Hardness, and pH:
Temperature: The ideal water temperature for growing Pearlweed is between the range of 19 – 28 °C (66 – 82 °F).
pH: Though adaptable to a range of conditions, the optimal pH level for this species is between 6.5 – 7.5.
Hardness: Pearlweed is a resilient plant, it will thrive in soft – hard water: 1 – 15 KH and 1 – 20 GH.
For this species to thrive, you need to provide moderate light intensity.
Pearlweed can also be used as a carpeting plant under high light. In most cases, bright illumination causes more compact, bushier growth with lots of runners. While low light will trigger upward growth with longer gaps between the leaf nodes. In addition, under low light, leaves become darker.
To promote optimal growth and ideal coloration in Pearlweed, maintain lighting for up to 10 hours daily.
Read more about it in my article “Advanced Guide to Planted Tank Lighting”.
Pearlweed can grow in any substrate, including sand and gravel. It does not require a nutrient-rich substrate to grow best.
CO2 and fertilization:
CO2 supplementation is not a necessity, the plant grows well in low-tech tanks, but its growth tends to be less bushy and dense.
With CO2 supplementation it will look much better as it promotes dense growth, spurs the growth rate, and facilitates pearling.
On the other hand, the addition of fertilizers is essential for nourishment. It keeps the plants in optimal condition and encourages the steady growth of shoots.
Pearlweed is mostly a water column feeder plant; its root system is pretty weak. The plant absorbs nutrients primarily through its leaves. Therefore, you need to dose liquid fertilizers, not root tabs.
Important: If you keep shrimp in the tank with Pearlweed, I would highly recommend reading my articles:
- CO2 in a Planted Tank Guide
- CO2 in a Shrimp Tank
- How Copper Affects Dwarf Shrimp
- Shrimp Safe Plant Fertilizers
The point is that a high level of CO2 and Copper (most fertilizers contain copper) is extremely dangerous to the shrimp.
Care and Maintenance of Pearlweed
Pearlweed is easy to care for and adaptable to a variety of conditions. However, you will be required to trim the foliage from to time to prevent it from overrunning the tank.
Its growth rate is highly dependent on nutrient availability, the intensity of lighting, and CO2 supplementation. Still, you need to check the plant’s growth and trim when necessary.
Until it takes hold, this species is actually not a rapid-grower.
After that and under optimal conditions with high light, Pearlweed will grow so rapidly you will have to cut it back weekly. One plant can make a small tank carpet in 2-3 months.
Without regular pruning, the plant will grow quite bushy and that’s good for the mid-ground/ background. Remember that a little trim occasionally will help keep things from going overboard.
As a foreground plant, the shoots will require constant and aggressive pruning with curved pruning scissors (link to check the price on Amazon) to maintain a short and compact form.
Moreover, heavy trimmings facilitates dense growth and formation of side shoots — giving you a somewhat carpet appearance. The bottom line is to cultivate and prune the foliage into the form or shape you desire in your aquarium.
Note: Pearlweed can make a wonderful carpet but it will be taller than Dwarf baby tears. Also, after trimming, the plant does not look very representative for a few days. Just keep that in mind.
|Tips on how to carpet:
Another important care activity is the regular addition of fertilizers. This should be liquid fertilizers such as Easy Green, Brightwell FlorinMulti, or the Seachem © product range of macronutrients and micronutrients, etc.
Ensure to read the product label and apply the fertilizer according to the manufacturer’s instructions. Fertilizer application will help the plant maintain a healthy and robust appearance while preventing adverse growth conditions such as stunted growth and yellowing of the leaves.
Routine partial water changes are required to maintain excellent water quality. Thus, replace the tank water with clean, dechlorinated water weekly and vacuum the gravel gently to get rid of mulm.
Planting and Propagation of Pearlweed
Like most stem plants, Pearlweed may be cultivated by placing the healthy stems into a substrate.
Whether pot or tissue culture variant split the plant into several portions and plant them in the substrate using a pair of aquarium tweezers.
While planting, place the stems gently into the substrate to avoid damaging the delicate stems. Few hobbyists use this plant as a floater in their planted tanks and quarantine tanks to create shades, while some grow it as a carpet — through careful planting.
Vegetative propagation is a sure way of multiplying the population of this stem plant. You can do this by clipping mature stems.
Next, form bundles of 2-3 stems each and place them in the substrate.
Under optimal conditions, the parent plants will regrow and branch out profusely to form dense vegetation whereas the new plants will root in the substrate and sprout new shoots.
Problems Associated with Pearlweed
Melting: One of the problems associated with Pearlweed is the phenomenon that often takes place when the plant is transferred from an emersed to a submersed environment.
This physical transfer/change in the environment triggers an adverse response in the plant; indicated by the gradual shedding of leaves in the first few weeks. I want you to understand that this is a normal occurrence in transferred stem plants. And when the plant settles fully in your aquarium — it will assume a submersed growth form, then develop new leaves.
Leggy bottom leaves: When Pearlweed gets really dense the bottom leaves will yellow and die back from lack of light.
Solution: Regular trimming prevents lower portions of the plant from becoming shaded. It will also maintain the bright green leaves.
Hard to plant: Pearlweed does not have a well-developed root system. It makes it really hard to plant because it may start floating a few hours later.
Solution: use small stones to keep it into the substrate or bury the long stems slightly deeper by tossing substrate on top of the plant. You can also let the plant float until you are ready to plant it.
Yellowing leaves: Other common problems include vertical, upward growth in dim lighting, as well as translucence/ yellowing of the leaves due to high pH levels or lack of essential nutrients needed for healthy growth.
Nitrates and phosphates: Pearlweed is highly dependent on nutrient availability in the water column. You can also have melting issues when nitrates and phospates get too low.
Solution: dose them regularly just to keep up with it.
- How to Spot Nutrient Deficiencies in Aquatic Plants
- Everything about Nitrates in Planted Tanks
- Phosphates in Freshwater Tanks
Benefits of Pearlweed
Aquascape: The shape and form of Pearlweed will be an excellent decorative addition for jungle aquascape.
Versatility: Pearlweed is one of a few plants that look good as a carpet, background, floating plant, or even as emersed/terrestrial form.
Removal of excess nutrients: I have already mentioned it as a problem but if you struggle with nitrates, Pearlweed will help you out. This plant absorbs and utilizes harmful chemicals that are emitted from fish waste, decayed plant matter, and tap water such as nitrates, ammonia, and phosphates.
Replacement: Once planted Pearlweed can be easily moved or removed. This plant has very thin and delicate roots. Do not worry, you will not pull up a big part of your substrate with it.
Hiding place: Serves as cover and shade for inverts and small fish. It serves as a perfect hiding place for shrimp and fish.
Foraging place: Acts as a buffet of biofilm, which is an ideal first food for newly hatched fry and shrimplets.
Oxygenation: Pearlweed oxygenates and aerates the tank water.
Pearlweed and Compatible Tankmates
This lush green plant is compatible with a wide variety of aquarium fauna.
It can be grown in freshwater aquaria with the following species of fish:
- Fish (for example, Bettas, Tetras, Pearl Guorami, Honey Guorami, Zebra Danio, Cherry Barbs, Platies, Guppies, Endlers, Mollies, Otocinclus Catfish, Pygmy Cory Catfish, etc.)
- Snails (for example, Japanese trapdoor snails, Ramshorn snails, Nerite snails, Malaysian Trumpet snails, Black Devil Snails, Asolene spixi, Rabbit Snails, etc.).
- Dwarf Shrimp (All varieties of Neocaridina (Red Cherry Shrimp, Blue Velvet Shrimp, Snowball shrimp, Black Rose, Orange Sakura, Green Jade, Rili Shrimp, etc) or Caridina species (for example, Crystal Red Shrimp, Caridina cf. babaulti, Blue Tiger Shrimp, etc.), Amano shrimp, Ghost shrimp, Bamboo shrimp, Vampire shrimp, ). Basically, you can keep any shrimp species with it. They will love it!
In fact, any small species of fish and invertebrate that will love to maneuver/explore the lush green bush created by the creeping Pearlweed shoots. Also, the plant is equally good for shrimp tanks, so do well to cultivate a few stems in your tank to provide dense foraging ground and hiding spots for your little inverts.
However avoid species that may find Pearlweed palatable, e.g. like Koi fish, Goldfish, Oscars, Rainbow, Jack Dempsey, Clown loaches, African Cichlids. These species can really cause problems in the planted tanks.
Unless you keep Pearlweed as a floating plant, do not keep it with most types of crayfish, or freshwater crabs. These animals will cut, eat, and uproot everything in the tank. So, be warned!
Despite its unavailability in the wild, this species is widely available and can be sourced from local fish stores and online aquarium stores.
Buyers are presented with two options: the pot variant and the tissue culture variant. The latter is lab-grown, and hence safer; eliminating the possibility of shipping with pest snails and algae. Regardless of the variant, a pot/cup/bunch of Pearlweed rarely costs more than $15 and that should be enough to aquascape a nano fish tank.
While shopping for Pearlweed, be sure to only obtain healthy specimens; plants having an overall healthy and bright green appearance — devoid of visible damages.
Before planting, make sure to disinfect the stems in a bleach solution to eliminate pest snails, algae, and parasites that can wreak havoc in the tank.
This procedure is not needed for tissue culture specimens i.e. plants grown in a sterile environment. Simply remove the plants from the cup, place them into a bowl of water and rinse off the nutrient gel.
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.
Pearlweed is a hardy stem plant utilized by hobbyists to beautify fish and shrimp tanks. It spreads vertically and horizontally (via runners) at the same time.
This amazing plant is suitable for beginners because of its minimal care requirement and ease of growing. Moreover, it can be cultivated in a variety of tanks regardless of their sizes.
Whether low-tech tank or high-tech tank, Pearlweed will thrive, and this bright green plant does an excellent job at decorating all sections of an aquascape with its attractive foliage.
The dense mat formed by Pearlweed serves as a fortress to juvenile fish and inverts. Lastly, the plant’s pearling trait is quite fascinating and it helps oxygenate the aquarium.