Acorus gramineus, commonly known as Japanese sweet flag, is widely used as a landscape plant in nurseries and gardening centers.
Acorus gramineus is a hardy, light-loving, and slow-growing plant. Its versatile nature makes it suitable for cultivation in paludariums, aquariums, and mini-ponds.
In this article, I will summarize everything known about Acorus gramineus from both the aquarist’s perspective and scientific data including care, maintenance, propagation, common issues, and more.
Interesting fact: For centuries, extracts of Acorus gramineus have been widely used in traditional Chinese medicine to treat and manage various human ailments, including central nervous system disorders. In Korean traditional medicine, it has been valued for its benefits in enhancing learning and memory, providing sedation, and offering analgesic effects.
Quick Notes about Acorus Gramineus
| Common Name | Japanese sweet flag |
| Other Names | Japanese rush, Grassy-leaved sweet flag, Slender sweet-flag, or Dwarf sweet flag |
| Scientific Name | Acorus gramineus |
| Difficulty | Easy |
| Lighting | Moderate |
| Optimal pH | 6.0 – 8.0 |
| Optimal GH | 4 – 20 |
| Optimal Temperature | 64– 82°F (18 – 22°C) |
| Substrate | Nutrient-rich |
| Can Be Grown Emersed | Yes |
| Growth Rate | Slow |
| Placement in Tank | Midground and background |
| Aquarium size | 10+ inches (over 25 cm) |
| Fertilizers | Needed |
| CO2 | Optional |
| Propagation | Through rhizomes |
| Color | Green |
Etymology
The genus name “Acorus” is derived from the Greek word “άκορος” (ákoros), meaning “pupil of the eye “, because it was used in herbal medicine as a treatment for inflammation of the eye.
The species name “Gramineus” comes from the Latin word “Gramineus,” meaning “Grassy” or “pertaining to grass”.
Taxonomy
Kingdom: Plantae (plants)
Infrakingdom: Streptophyta (land plants)
Clade: Angiosperms (flowering plants)
Clade: Monocots (a single seed leaf)
Order: Acorales (acorus order)
Family: Acoraceae (sweet flag family)
Genus: Acorus (sweet flag)
Species: Acorus gramineus (grassy-leaved sweet flag)
Distribution
Acorus gramineus is mainly found in Eastern Asia, including Korea, China, and Japan. However, it was also reported in the Russian Far East, Bangladesh, Cambodia, Laos, Myanmar, Vietnam, Thailand, Mongolia, India, and Eastern Europe.
In some regions, such as the United Kingdom and Virginia, Acorus gramineus is even considered an invasive species.
Habitat
Acorus gramineus is usually found in wetlands (partially or completely submerged), particularly marshes and river banks, where the land is saturated with water.
Description
Acorus gramineus is an aquatic to semi-aquatic perennial herbaceous plant with semi-evergreen grasslike foliage. This plant grows with submersed and emersed plant parts.
- Size: The plant generally reaches a height of 12 to 20 inches (30 – 50 cm). The width is often around 8 to 12 inches (20 – 30 cm).
- Leaves: The leaves are narrow, grass-like, and sword-shaped.
The leaves are arranged in two rows, resembling opposing fans, and are flat and usually 0.1 – 0.4 inches (0.3 to 1 cm) in width.
Note: They have a distinct aromatic scent when crushed.
- Color: The leaves are bright green.
- Rhizome: Acorus gramineus has a creeping, aromatic rhizome that is horizontal and can be quite thick (up to 0.4 inches or 1 cm) and long (2 to 4 inches or 5 – 10 cm). The rhizome is pale yellow to brownish on the outside and white on the inside.
- Flowers: The plant produces small, inconspicuous green-yellowish flowers arranged on a cylindrical spike called a spadix, which is usually hidden among the foliage. The spadix is about 2 to 4 inches (5 – 10 cm) long. It flowers only when it is partially submerged in water.
- Grow forms: When grown in paludariums with its rhizome above the water (emergent Form), Acorus gramineus displays its typical height and dense, upright foliage. This form is commonly used in garden borders, ponds, and wetland restorations. They tend to arch over, giving the plant a graceful appearance.
When grown in aquariums or as a submerged plant in water gardens, Acorus gramineus tends to be smaller and more compact. The leaves might be shorter and less rigid compared to those in the emergent form. Submersion can also impact the growth rate and leaf texture, making them softer.
| The most popular varieties of this plant are Ogon (noted for its luxurious golden leaves) and Variegata (characterized by dark green leaves edged with pale yellow margins). |
Tank Requirements and Water Parameters
Tank size:
Due to its significant size, Acorus gramineus can only be suited in larger aquariums (or paludariums) starting from 20 gallons (80 liters).
However, even in such an aquarium, over time, this plant may become so large that you will have no choice but to trim and divide it.
Water type, Temperature, Hardness, and pH:
Temperature: Acorus gramineus is a very hardy plant. It can tolerate a wide range of temperatures (from 39 – 86°F or 4 to 30°C). However, the ideal temperature for this plant is between 64 – 82°F (18 – 22°C).
pH: pH level between 6.0 – 8.0 is considered optimal for growing this plant.
Hardness: The plant can also adapt to a wide range of water hardness values (4 – 20 GH).
Related article:
Lighting:
Acorus gramineus requires moderate to high lighting. Providing it with full spectrum lighting for 10-12 hours a day is generally suitable.
In aquariums, it can also tolerate lower light conditions as well. In nature, this plant can be found growing in semi-shaded areas. So, if you have a low-tech tank, this plant can also be a good choice. However, its growth rate will be significantly lower.
Related article:
Flow:
It is not mandatory but a mild flow helps prevent algae growth and keeps the plant healthier by ensuring better oxygenation and nutrient distribution.
Nonetheless, this plant will thrive even in still water as well.
Substrate:
Acorus gramineus prefers loose, nutrient-rich substrates. In nature, this species comes up well in clayey loams and light alluvial soils of river banks.
Related article:
CO2 and Fertilization:
CO2: CO2 supplementation contributes to the overall growth and health of aquarium plants, but in this case, it is not mandatory as the species can thrive with or without it.
Fertilizers: On the other hand, fertilizers are required. Be sure to regularly dose (2 times a week) plant fertilizers in the aquarium water to keep the plant in the best condition.
Important: If you keep shrimp in the tank with Acorus gramineus, 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
In a Paludarium:
- Watering: This wetland plant requires more water than most species. The rhizome should never dry out. Keep the substrate consistently moist, and consider placing the pot in a shallow dish of water.
- Humidity: High humidity is crucial. Maintain the plant on a tray of moist gravel year-round and mist the foliage during warmer months.
- Fertilization: Feed the plant with a standard liquid fertilizer every two weeks during spring and summer.
In a Pot:
- Soil: Plant in shallow pots or trays in a mix of peat and compost, with a bit of soil.
- Watering: Ensure the soil remains constantly damp. The plant requires consistently moist conditions.
In an Aquarium:
- Maintenance: Requires minimal care due to its slow underwater growth.
Planting
In aquascaping, Acorus gramineus can be only used as a background plant due to its larger size. It can easily serve as a focal point.
You simply need to plant it deeply enough in the substrate to keep it from floating up; there is no special method or trick involved in the planting process itself.
Plant the rhizome pieces in the substrate of the aquarium, spacing them 10×10 inches (25 x 25 cm) apart. Ensure they are buried about 1 inch (2.5 cm) deep.
Propagation
Acorus gramineus is propagated through rhizomes.
Rhizomes are divided by cutting the roots to create smaller clumps, each with a well-developed root system, which ensures successful growth when replanted.
Problems Associated with Growing Acorus Gramineus
Insufficient light: The plant prefers good lighting. However, too much light can also cause leaf scorching and damage.
Overcrowding: In both aquariums and paludariums, overcrowding can limit space and resources, leading to competition and stunted growth.
Slow growth underwater: In aquariums, the plant’s slow growth underwater may require patience and ongoing care to ensure it establishes and thrives.
Humidity levels: In paludariums, low humidity can lead to suboptimal growth. Acorus gramineus prefers high humidity levels.
Leaf tip drying: In paludariums, a common issue is the drying of leaf tips due to insufficiently moist soil. Ensure the substrate remains consistently damp to prevent this problem.
Relocation: If you need to relocate this plant or remove it for propagation, exercise extreme caution due to its extensive and robust root system. Avoid pulling it out by hand, as this could disturb a substantial portion of the substrate in your tank.
Related article:
- How to Spot Nutrient Deficiencies in Aquatic Plants
- Everything about Nitrates in Planted Tanks
- Phosphates in Freshwater Tanks
Benefits of Acorus Gramineus
Aquascape: Acorus gramineus can be an excellent decorative addition to your tank.
Hiding place for fish, fry, and shrimp: Acorus gramineus serves as great cover and shade for inverts, small frogs, and fish.
Foraging place: Acts as a buffet of biofilm, which is an ideal first food for newly hatched fry and shrimplets.
Prevents gas pockets: Acorus gramineus 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.
Quarantine Acorus Gramineus
Unless you are completely sure that Acorus gramineus is safe, for example, it was grown in sterile/laboratory conditions (in vitro) and 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
Overall, Acorus gramineus is a versatile plant that adapts well to both semi-aquatic and aquatic environments.
The plant is not demanding in terms of water quality, making it ideal for beginner aquarists.
The only downside though is that it is not suitable for small aquariums.
References:
- Park, Cheol Hyeong, Ki Hyun Kim, Il Kyun Lee, Seung Young Lee, Sang Un Choi, Jei Hyun Lee, and Kang Ro Lee. “Phenolic constituents of Acorus gramineus.” Archives of pharmacal research34 (2011): 1289-1296.
- Chen, Qi-Xiong, Jing-Kun Miao, Chun Li, Xiao-Wen Li, Xiao-Mei Wu, and Xiao-ping Zhang. “Anticonvulsant activity of acute and chronic treatment with a-asarone from Acorus gramineus in seizure models.” Biological and Pharmaceutical Bulletin36, no. 1 (2013): 23-30.
- Balakumbahan, Ramachandran, K. Rajamani, and K. Kumanan. “Acorus calamus: An overview.” Journal of Medicinal Plants Research4, no. 25 (2010): 2740-2745.
- Wu Zheng-yi, Peter H. Raven, Deyuan Hong (eds.):Flora of China. Volume 23: Acoraceae through Cyperaceae , Science Press and Missouri Botanical Garden Press, Beijing and St. Louis, 2010.