Willow hygro (Hygrophila angustifolia) is one of the easiest aquarium plants to keep. With its attractive foliage and ease of growth, Hygrophila angustifolia has become a staple aquarium plant for hobbyists worldwide.
Whether you are new to the hobby or a seasoned aquarist, this attractive aquatic plant can make a fantastic addition to your tanks, especially if you’re looking to lower the levels of nitrogenous compounds.
However, it is also worth noting right from the beginning that because of its rapid growth, Willow Hygro has a tendency to spread and can easily take over your tank, which is why some enthusiasts refer to it as a “weed.”
In this article, I will explore the background, growth habits, recommended care, and propagation of Hygrophila angustifolia.
Quick Notes about Willow Hygro
| Common Name | Hygrophila angustifolia |
| Other Names | Willow hygro, Willow leaf hygro, and Giant hygro |
| Scientific Name |
Hygrophila corymbosa var augustifolia/ Hygrophila Angustifolia |
| Difficulty | Easy |
| Lighting | Moderate to High |
| Optimal pH | 6.6 – 8.0 |
| Optimal GH | 6 – 20 |
| Optimal Temperature | 68 – 82°F (20 – 28°C) |
| Substrate | nutrient-rich |
| Can Be Grown Emersed |
Yes |
| Growth Rate | Fast |
| Placement in Tank |
Background |
| Aquarium size | 12 – 40 inches (60 – 100 cm) |
| Fertilizers |
Optional |
| CO2 | Optional |
| Propagation | Stem cuttings and lateral shoots |
| Color |
Green |
Interesting fact: Studies have shown that Hygrophila angustifolia possesses antimicrobial properties.
Taxonomy Problems of Genus Hygrophila
In aquarium hobby, Hygrophila angustifolia and Hygrophila corymbosavar’ angustifolia’ are often used interchangeably. However, some people believe that these are two different (although very similar) plants.
In reality, the situation is extremely confusing.
Let’s begin with the fact that according to official sources, there are between 46 to 100 species of Hygrophila!
Yes, you heard that right—even scientists can’t agree on the number of Hygrophila species. As a result of all this conflicting information, it is not even possible to distinguish between artificial forms of aquarium plants and their natural counterparts anymore.
The good thing though is that the care requirements are the same regardless of the exact taxonomy name.
Therefore, purely for brevity, I will simply refer to it as Hygrophila angustifolia moving forward when discussing this plant.
Etymology of Hygrophila Angustifolia
The genus name “Hygrophila” is derived from the Greek words “Hygro” meaning moisture/wetness and “Philos” meaning loving or friendly. It indicates its wetland habitat preference.
The word “Angustifolia” is a combination of the Latin words “Angustus” which means narrow, and “Folium,” which means leaf. It refers to the relatively narrow leaves of this species.
Together the scientific name Hygrophila angustifolia translates to “moisture-loving plant with narrow leaves”.
Distribution of Willow Hygro
Hygrophila angustifolia can be found in tropical and subtropical regions of Asia, including northern and southern Vietnam (Tonkin, Cochinchina), Cambodia, Borneo, China (Yunnan, Sichuan, Hong Kong), Malay Peninsula, Java, Sumatra, Thailand, Indonesia, north-western Australia, New Zealand, New Guinea, and Japan.
Habitat of Willow Hygro
It likely originated in the wetlands and rice paddies of mainland Southeast Asia.
This species grows along the banks of streams, rivers, ponds, and rice paddies. It prefers wet soil, still or slow-flowing, and shallow water. It is commonly found in flooded areas, ditches, swamps, and marshes. This allows Willow hygro to adapt to the periodic changes between rainy and dry seasons.
Description of Willow Hygro
With its bushy green foliage, Hygrophila angustifolia makes an impressive background plant in the aquarium.
Distinguishing characteristics:
- Growth habit. This is a freshwater, erect, perennial, herbaceous plant.
- Height. It can grow quite tall in the aquarium, typically reaching 12 – 40 inches (60 – 100 cm) high and 10-12 inches (25-30 cm) wide.
- Stem. The stems are hard and square-shaped up to 0.2 inches (5 mm) thick.
- Leaves. The leaves are narrow and pointed, typically 1-6 inches (2.5-16 cm) long and 0.3-0.6 (8-15 mm) wide. They emerge from the stem in pairs and have smooth margins or the edges of the leaves develop a slight wave. The color range varies from pale green to emerald. The lower part of the leaf blade is lighter. Under bright light, it acquires a red-brownish tint. The underside is silvery.
- Flowers. The small flowers occur in clusters in the joint between the leaves and stem. Each flower has a calyx (sepals) 0.3 – 0.4 inches (8-10 mm) long and a corolla (petals) that are usually white with blue or purple markings. The corolla tube is 0.2-0.3 inches (6-8 mm) long and the lobes are 0.12-0.16 inches (3-4 mm). The flowers open in the morning and close during the day.
- Roots. It develops a very powerful root system.
- Emergent growth. Hygrophila angustifolia can grow partially or fully emergent above the water surface.
This plant exhibits considerable morphological variability between different geographical varieties, and environmental conditions, particularly in leaf shape and size, hairiness, and flower characteristics.
Tank Requirements and Water Parameters
This is a beautiful and so undemanding plant that many aquarists put it into the category of nearly un-killable.
Both beginner and experienced aquarists can appreciate this low-maintenance yet striking aquatic plant. With the right care and trimming, Hygrophila angustifolia’s lush appearance helps create an aquatic landscape that immediately catches the eye.
In paludariums (emersed form), this plant becomes pretty hardy and does not require too much more attention and care.
Tank size:
Due to its significant size and fast growth rate, Hygrophila angustifolia can only be suited in larger (high, especially) aquariums starting from 20 gallons (80 liters).
This plant also requires space to spread horizontally. Over time, this plant may become so large (since it produces a huge number of leaves) that you will have no choice but to trim and divide it.
Water type, Temperature, Hardness, and pH:
Temperature: Willow hygro does best in warm tropical temperatures from 68 – 82°F (20 – 28°C). This plant does not tolerate cold water. If the temperature drops below 68°F (20°C) it starts growing slowly.
pH: This plant prefers water pH in the range of 6.5 – 8.0. Basically, a slightly acidic pH is found to be more suitable. It was noticed that too acidic water negatively affects its leaves and root system.
Hardness: It can grow in soft and hard water GH 6-20. However, old leaves are much better preserved in hard water (in soft water they decay faster, and the plant has to be propagated more often).
Lighting:
Willow hygro requires powerful illumination (>40 PAR). Under bright lighting, the pronounced central vein of the leaf acquires a red-brownish color. Full exposure to light maximizes growth.
The photoperiod should be about 12 hours.
Despite the love of this plant for light, it easily tolerates long-term shading well. But with insufficient lighting, the leaves become smaller, acquire a yellowish tint, and the stem elongates and becomes leggy.
Related article:
Flow:
Hygrophila angustifolia can tolerate moderate water movement, but avoid strong currents.
Its long leaves add movement and dimension while the dense growth provides a jungle-like backdrop.
Substrate:
Nutrient-rich substrate is optimal for Hygrophila angustifolia. The substrate depth should be at least 2 inches (5 cm). This plant is a heavy root feeder, even though it is also able to extract huge amounts of nutrients from the water column.
Keeping Hygrophila angustifolia in sand or gravel is also very possible. However, you will have to either regularly use root tabs or liquid fertilizers to help it out. Some aquarists attach it to driftwood, or sometimes even left floating in the aquarium.
This is a very versatile plant.
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CO2 and fertilization:
CO2: CO2 supplementation is optional. Hygrophila angustifolia can grow in low-tech tanks, but its growth tends to be slower and less bushy. Nonetheless, as with most aquatic plants, its addition will positively impact the plant’s growth rate and appearance.
Fertilization: As I have already mentioned, although Willow hygro has a large root system, the plant also feeds from the water column. While undemanding by nature, this plant does respond quite favorably to fertilizers.
Important: If you plan to add this plant in a shrimp tank or high-tech planted tank with CO2 and regular fertilization, 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 Willow Hygro
- Hygrophila angustifolia develops excellently in large and tall aquariums.
- It is easy to care for, and you won’t run into many problems with this plant.
- Depending on the conditions, this plant has a moderate to very fast growth rate in the aquarium. Experiments showed that under optimal conditions, the plant can increase its biomass almost 6 times in 30 days.
- Propagation boosts its growth. Regular propagation by trimming and replanting stems can accelerate growth and create a dense bush. Pinching stem tips prompts branching.
- Underwater, it demonstrates its best decorative qualities. Do not allow it to grow above the surface.
Trimming Willow Hygro
Once the plant is about to touch the surface or there are already emerging lower shoots aiming to grow taller – it is time for trimming. The trimmed parts can be placed back into the substrate where they readily develop roots.
It may be very hard to trim long plants. However, if you trim plants and do water changes at the same time it may become very easy.
- Lower the water volume in the tank to use it as a measurement.
- Pull the stem
- Trim Willow hygro about at water level.
Propagation of Willow Hygro
Hygrophila angustifolia can be propagated in several ways in an aquarium.
- Stem cuttings: The easiest method is taking 5-6 inch stem cuttings from the tops of mature stems. Cut between the nodes. Each fragment should have at least a few leaves.
- Lateral shoots: Lateral shoots are side branches that develop from the main plant’s nodes. These lateral shoots can be cut and planted in a substrate.
- Horizontal: You can also lay the stem horizontally, and from each node, a new stem will emerge. This is one of the fastest ways to increase the number of plants.
Planting Willow Hygro
Hygrophila angustifolia is suitable for placement in the background of planted tanks due to its huge size and bushy appearance.
Preparation. If you have a potted Hygrophila Angustifolia, gently remove it from the pot, being careful not to damage the roots or stems. If you have stem cuttings or lateral shoots, make sure they are healthy and free from any damaged or decaying parts (remove them if needed).
Planting. The roots should be buried in the substrate. Ensure that the roots are adequately covered to promote stability and nutrient absorption. If you have a stem cutting without roots, plant it in a way that the node is completely submerged in the substrate. Over time, roots will develop from it, securing the plant in place.
Depth. The recommended planting depth for the node of a Hygrophila angustifolia stem cutting is typically about 1 to 2 inches (2.5 to 5 centimeters) deep in the substrate. This depth allows the node to be securely anchored in the substrate.
Spacing: Space the plants appropriately, leaving enough room between them to allow for growth. Avoid planting Hygrophila angustifolia in one large clump, place them at least 3 – 4 inches (7 – 10 cm) apart from each other to achieve a good spread.
If you see that the plant is getting old but it is still quite healthy, you can do the following steps:
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Problems Associated With Growing Willow Hygro
Leggy. One of the most common problems is its tendency to become leggy. The plant grows tall and thin with excessive stem length between leaves, often resulting in a less attractive appearance and reduced overall plant health. It can also drop old leaves.
Solution: Improve lighting, nutrient balance, and prune the plants.
White hears/roots. When the plant reaches the surface, it often starts developing white hairs, which can appear highly unattractive.
Solution: Do not allow it to reach the surface. Prune the plant regularly.
Overgrowth: Hygrophila angustifolia is a fast-growing plant and it may overrun the tank if left unattended in no time. In addition, they will create shades thereby blocking light from getting to plants at the bottom of the tank.
Solution: The dense mass should be pruned and discarded from time to time to prevent overcrowding and shadowing at the surface.
Relocation: If someday, you decide to relocate the old Hygrophila angustifolia, it can turn into a real problem. This plant forms large MASSIVE roots that can uproot a huge part of your tank.
Solution: The only thing I can think of is to be careful and take it out very slowly and do it while siphoning the tank.
Related articles:
- How to Spot Nutrient Deficiencies in Aquatic Plants
- Everything about Nitrates in Planted Tanks
- Phosphates in Freshwater Tanks
Benefits of Willow Hygro
Versatility: Willow hygro is one of the plants that can grow emersed and submersed. It can grow in low and high-tech tanks.
Prevents gas pockets: This plant has a well-developed root system that will help to break up anaerobic pockets in the substrate.
Note: Hydrogen sulfide pockets (H2S, the gas smells like rotten eggs) can be really dangerous to your fish or shrimp.
Removal of excess nutrients: As a fast-growing plant, Willow hygro will absorb and utilize harmful chemicals that are emitted from the animals’ waste, decayed plant matter, and tap water such as heavy metals, ammonia, nitrates, etc.
According to the study, these are the changes in concentrations of NH4 (ammonium), NO2 (nitrites), and NO3 (nitrates) in aquarium water after 48 hours.
| NH4 | NO2 | NO3 | |
| Hygrophila angustifolia | 2.3-1.6 | 0.197-0.15 | 21.4-20.1 |
Reduces algal bloom: This plant helps in reducing the overall probability of algal bloom in the given environment. The plant is pretty greedy for nutrients. So, it simply outcompetes algae.
Hiding place for fish, fry, and shrimp: It will serve as an excellent cover and hiding place for inverts and small fish. They love to play in it and pick on it.
Foraging place: Acts as a buffet of biofilm, which is an ideal first food for newly hatched fry and shrimplets.
Quarantine Willow Hygro
Unless you are completely sure that Hygrophila angustifolia is safe, for example, it was grown in sterile/laboratory conditions (in vitro) and the in vitro pot is not damaged or opened, do not forget to quarantine and disinfect it first to avoid the risk of contamination and poisoning.
DO NOT introduce a new plant to your tank right after you bought it.
- The plant can have parasites, pests like snails, or even predators (dragonfly, damsefly nymphs, etc.).
- It may already contain residues of chemicals (pesticides) to remove parasites, snails, etc. These chemicals are extremely poisonous to fish, shrimp, and other invertebrates.
To find out more, read my articles:
In Conclusion
Having moved from rice paddies into aquariums, Hygrophila angustifolia is a great find for a beginning aquarist. The fast-growing and long-leaved Hygrophila is absolutely undemanding in care. It can grow in all kinds of substrate, without fertilization or CO2, in the shade, underwater, above the water, quickly adapts to almost any conditions, and absorbs nitrates like a sponge.
At the same time, it should be noted that many of these advantages can, over time, become a burden for the aquarist because this plant, without proper control, can become invasive and simply take over everything it can.
References:
- Yoshino, Hiroyuki, Daniel E. Gruenberg, Isamu Watanabe, Katsumi Miyajima, Osamu Satoh, and KatsuakiNashimoto. “Changes in Water Quality and Performance of a Closed Recirculating Aquaculture System for Pejerrey (Atlantic Silversides).” In Symposium 2-International Recirculating Aquaculture System.
- Saenger, Peter. “A survey of the tidal and non-tidal wetland plants of the Pungalina Seven Emu conservation area on the Calvert River, Northern Territory.” Pungalina Wetlands Scientific Study Report(2017): 57.
- Nadu, Tamil. “Journal of Pha Biologic.” (2016)
- Contribution à la flore des Acanthacéesasiatiques; (2e Note) Bulletin de la SociétéBotanique de France: Vol. 60, No. 3, pp. 266-273.
- Cowie, Short, Osterkamp Madsen (2000) “Floodplain Flora, a flora of the floodplain of the Northern Territory, Australia”.
- Hu Jiaqi, Deng Yunfei, Daniel T. F. Acanthaceae // Flora of China / Editors: Wu, Z. Y., P. H. Raven & D. Y. Hong. — St. Louis: Science Press, Beijing, and Missouri Botanical Garden Press, 2011. — Vol. 19 (Cucurbitaceae through Valerianaceae, with Annonaceae and Berberidaceae). — С. 468–469.
- http://www.theplantlist.org/tpl/record/kew-2856689