The Versatile Pearlweed: A Guide to Planting, Growing, and Maintenance


Pearlweed, also known as Hemianthus micranthemoides, is a popular and versatile aquatic plant species that adds beauty to freshwater aquariums. Renowned for its vibrant green color and adaptability, Pearlweed can be used as a foreground, mid-ground, or background plant, depending on the desired aquascape. In this article, we will explore everything you need to know about Pearlweed and how to successfully plant and care for it in your freshwater tank.

Quick Notes about Pearlweed

  • Common Name: Pearlweed
  • Other Names: HM, Baby tears, Pearl weed, Manatee mudflower, Amano pearl grass, Pearl grass
  • Scientific Name: Hemianthus micranthemoides or Hemiánthus glomerátus
  • Tank Size (minimum): 5 gallons (~20 liters)
  • Difficulty: Easy
  • 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
  • Fertilizer: Recommended
  • CO2: Not needed but recommended
  • Propagation: By clipping mature stems

The Origin of Pearlweed and Potential Misidentification

Pearlweed, scientifically known as Hemianthus micranthemoides, is a well-known aquarium plant that belongs to the Scrophulariaceae family. However, it is often mistaken for Hemianthus callitrichoides due to their similar appearance, although Hemianthus micranthemoides has larger foliage. While there is some confusion regarding the taxonomy of this plant, it is still widely available in the aquarium trade thanks to cultivation and preservation efforts. Further research is needed to properly classify Pearlweed.

Habitat of Pearlweed

Pearlweed is native to the Mid-Atlantic region of the United States, where it grows in tidal rivers with gravel or sandy substrates. It prefers areas with sufficient water movement.

Description of Pearlweed

Pearlweed is a low-growing stem plant with vibrant green leaves that form attractive vegetation in aquascapes. Its small, ovate leaves grow in whorls of 3-4 along delicate, thin stems. Under low lighting, the plant grows upright, while under intense lighting conditions, it forms dense mats. The leaves produce oxygen bubbles through photosynthesis when provided with optimal light levels and CO2 supplementation.

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Tank Requirements and Water Parameters

Tank size: Pearlweed can be grown in tanks of various sizes, including nano tanks with a volume of 5 gallons (~20 liters). However, it is best suited for tanks of at least 10 gallons (~40 liters) to allow for its growth.

Water type, Temperature, Hardness, and pH:

  • Temperature: The ideal water temperature for Pearlweed is between 19 – 28 °C (66 – 82 °F).
  • pH: Pearlweed can adapt to a range of pH conditions but thrives in a pH level of 6.5 – 7.5.
  • Water hardness: It can tolerate soft to hard water conditions, with a range of 1 – 20 GH (general hardness).

Lighting: Moderate lighting is sufficient for Pearlweed to thrive. However, under high lighting, it can be used as a carpeting plant, resulting in compact, bushy growth with numerous runners. Low light conditions promote upward growth with longer gaps between leaf nodes, resulting in darker leaves.

Substrate: Pearlweed can grow in various substrates, including sand and gravel. It does not require a nutrient-rich substrate to grow well.

CO2 and fertilization: CO2 supplementation is not necessary for Pearlweed, but it is recommended for optimal growth. The addition of fertilizers is essential to provide the necessary nutrients for the plant’s health and steady shoot growth. Pearlweed is primarily a water column feeder plant and absorbs nutrients through its leaves. Liquid fertilizers should be used instead of root tabs.

Care and Maintenance of Pearlweed

Pearlweed is a relatively low-maintenance plant but may require occasional trimming to prevent it from overrunning the tank. Its growth rate depends on the availability of nutrients, lighting intensity, and CO2 supplementation. Regular monitoring and trimming are necessary to maintain the desired shape and prevent excessive growth.

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Growth rate: After taking hold, Pearlweed grows rapidly under optimal conditions, requiring weekly trimming to control its growth. With high light levels, this plant can carpet a small tank in just 2-3 months.

Trimming: Regular pruning is essential to maintain the desired shape of Pearlweed. Without pruning, the plant can become bushy, especially in the mid-ground and background. Curved pruning scissors are recommended for trimming shoots to achieve a short and compact form. Heavy trimmings promote dense growth and the formation of side shoots, creating a carpet-like appearance. After trimming, the plant may not look representative for a few days, but it will recover.

Feeding: Liquid fertilizers should be regularly added to provide essential nutrients for Pearlweed’s growth and prevent nutrient deficiencies. Routine partial water changes and gravel cleaning are also important to maintain excellent water quality.

Planting and Propagation of Pearlweed

Like most stem plants, Pearlweed can be propagated by placing healthy stems into the substrate. Whether using pot or tissue culture variants, split the plant into several portions and plant them carefully using tweezers. Some hobbyists also use Pearlweed as a floating plant or as a carpet by meticulous planting. Vegetative propagation is achieved by clipping mature stems and bundling them into the substrate. Under optimal conditions, the parent plants will regrow and branch out, while the new plants root in the substrate and sprout new shoots.

Problems Associated with Pearlweed

Some common problems associated with Pearlweed include melting during the transition from emersed to submersed growth, leggy bottom leaves caused by shading, difficulty in planting due to its weak root system, and yellowing leaves due to high pH levels or nutrient deficiencies. Regular trimming, adequate lighting, and nutrient supplementation can help mitigate these issues.

Benefits of Pearlweed

Pearlweed offers several benefits in freshwater aquariums:

  • Aquascape: Its shape and form make Pearlweed an excellent decorative addition, especially in jungle aquascapes.
  • Versatility: Pearlweed can be used as a carpet, background, floating plant, or even in its emersed/terrestrial form.
  • Excess nutrient removal: Pearlweed absorbs and utilizes harmful chemicals emitted from fish waste, decayed plant matter, and tap water, helping to maintain water quality.
  • Replacement: Once planted, Pearlweed can be easily moved or removed without disturbing the substrate.
  • Hiding place: Pearlweed provides cover and shade for invertebrates and small fish, serving as a perfect hiding place.
  • Foraging place: The plant acts as a buffet of biofilm, providing an ideal first food for newly hatched fry and shrimp.
  • Oxygenation: Pearlweed oxygenates and aerates the tank water.
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Pearlweed and Compatible Tankmates

Pearlweed is compatible with a wide variety of aquarium fauna, including small fish (such as Bettas, Tetras, and Cory Catfish), snails, and dwarf shrimp (such as Neocaridina and Caridina species). It provides a lush green bush for them to maneuver and explore.

However, Pearlweed should not be kept with species that find it palatable, such as Koi fish, Goldfish, Oscars, Rainbow Fish, Jack Dempsey, Clown Loaches, and African Cichlids. Additionally, caution should be exercised when keeping Pearlweed with crayfish or freshwater crabs, as they may damage or uproot the plant.

Buying and Quarantining Pearlweed

Pearlweed is widely available for purchase from local fish stores and online aquarium stores. Buyers can choose between pot and tissue culture variants, with tissue culture plants being more reliable and free from pests and algae.

Before planting, it is advisable to disinfect the stems to eliminate pest snails, algae, and parasites. However, tissue culture plants do not require this step. Proper quarantine and disinfection protocols should be followed to ensure the health of the plants and the aquarium.

In Conclusion

Pearlweed is a versatile and easy-to-care-for aquatic plant that brings beauty to freshwater aquariums. Its vibrant green color, adaptability, and ability to grow in various tank sizes make it a popular choice among hobbyists. Whether used as a foreground, mid-ground, or background plant, Pearlweed adds an attractive touch to any aquascape, providing hiding places, foraging spots, and oxygenation to the tank. With proper care and maintenance, Pearlweed can thrive and enhance the overall aesthetic of your freshwater aquarium.