Water Milfoil: Caring for Myriophyllum aquaticum
- aquaterraobsession
- Jan 31
- 8 min read
Aquatic Plant Care Sheet
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This care sheet is a practical guide for successful cultivation and aquascaping with Myriophyllum aquaticum.
Table of Contents
Introduction and Taxonomy
Myriophyllum aquaticum, commonly known as Parrot's Feather, is a perennial aquatic herb belonging to the Haloragaceae family. It is distinct among aquarium plants for its feather-like foliage and its tendency to grow as an emergent species, meaning it often extends above the water surface while rooted underwater.
Taxonomically, the genus Myriophyllum (Water Milfoils) contains roughly 69 species. M. aquaticum is perhaps the most recognizable due to its robust growth and blue-green, waxy emersed leaves. While valued in the aquarium and pond hobby for its aesthetic texture and nutrient-absorbing capabilities, it is also widely recognized as an invasive species in many non-native regions due to its rapid vegetative reproduction and lack of natural predators outside its home range.
Summary Table of Ideal Care Parameters
Parameter | Ideal Range | Notes |
Difficulty | Easy to Moderate | Generally hardy but requires high light to prevent legginess. |
Placement | Background / Floating | Best used as a background stem or floating surface plant. |
Lighting | High to Very High | Essential for tight internodes and healthy lower leaves. |
Temperature | 64°F - 78°F (18°C - 26°C) | Can tolerate lower temperatures; often grown in ponds. |
pH | 6.0 - 7.5 | Adaptable to a wide range of acidity. |
General Hardness (GH) | 3 - 15 dGH | Tolerates soft to moderately hard water. |
Carbonate Hardness (KH) | 3 - 8 dKH | Standard buffering capacity is sufficient. |
TDS | 100 - 400 ppm | Not highly sensitive to dissolved solids. |
Water Flow | Low to Moderate | Prefers gentler flow; high flow can damage delicate submersed leaves. |
Substrate | Nutrient-rich soil or sand | Root feeding is beneficial, but it feeds heavily from the water column. |
CO2 | Recommended (15-30 ppm) | Not strictly required, but significantly improves density and growth speed. |
Fertilization | Moderate to High | Heavy feeder, specifically of Nitrates and Iron. |
Growth Rate | Fast to Very Fast | Can grow several inches per week under optimal conditions. |
Propagation | Cuttings | Stem division is the primary method. |
Compatible Species | Small community fish, shrimp | Good shelter for fry; avoid large herbivores. |
Maintenance | High | Requires frequent trimming to prevent shading of lower levels. |
Common Issues | Legginess, Algae on leaves | Lower leaves often melt if light is insufficient. |
Cultivars | 'Dwarf', 'Red Stem' | Variations are rare; standard form is dominant. |
Native Range and Geographic Distribution
Myriophyllum aquaticum is native to the Amazon River basin in South America, specifically found in Brazil, Peru, and Chile.
Due to its popularity in the aquarium and water garden trade, it has been introduced globally. It is now established in North America, Europe, South Africa, Japan, and Australia. In many of these regions, specifically the United States and the European Union, it is classified as a noxious weed or invasive species because it outcompetes native flora and alters local aquatic ecosystems.
Natural Habitat and Environmental Conditions
In its native range, Myriophyllum aquaticum inhabits slow-moving or stagnant freshwater bodies such as wetlands, shallow lakes, ponds, and canal margins.
Light Exposure: The plant thrives in full sun environments. In the wild, it forms dense floating mats that absorb unobstructed sunlight. It is rarely found in deeply shaded forest streams, as its high metabolic rate requires significant photosynthetic energy.
Substrate: It typically roots in muddy, nutrient-rich substrates composed of silt and organic detritus. However, it is highly adaptive and can exist as a free-floating mat where its roots hang in the water column, extracting nutrients directly from the water rather than the soil.
Water Quality: The waters in its native habitat are generally warm and nutrient-rich (eutrophic). It is capable of tolerating fluctuations in water level, surviving periods where the water recedes, leaving the plant stranded on wet mud (terrestrial form).
Morphological and Growth Characteristics
Myriophyllum aquaticum exhibits heterophylly, meaning it produces different leaf forms depending on whether it is growing above or below the water surface.
Stems: The stems are robust, reaching up to 5-6 feet in length in the wild. They are brittle and snap easily, which aids in propagation.
Leaves (Submersed vs. Emersed):
Submersed Form: Leaves are finely pinnate (feather-like), typically bright green to reddish-brown. They are delicate and limp, collapsing when removed from water.
Emersed/Emergent Form: As the stem breaks the water surface, the leaves change drastically. They become stiff, waxy (hydrophobic), and blue-green (glaucous) in color. These leaves are arranged in whorls around the stem and resemble miniature fir trees.
Root System: The plant develops adventitious roots at the nodes (where leaves join the stem). These roots are long, white, and fibrous, designed to anchor the plant or absorb nutrients from the water column when floating.
Flowers: The plant is dioecious, meaning male and female flowers grow on separate plants. However, in most introduced ranges (including North America), only female plants are present. The flowers are small, white, and inconspicuous, forming in the axils of the emersed leaves. Because male plants are rare outside South America, reproduction is almost exclusively vegetative.
Growth Habit: It grows as a rhizomatous perennial. In an aquarium, it will grow vertically until it hits the surface, then grow horizontally, forming a canopy.
Ideal Water Parameters
Myriophyllum aquaticum is not overly fussy about water chemistry, but stability helps prevent leaf melt.
pH: 6.0 to 7.5. It prefers neutral to slightly acidic water but tolerates alkalinity.
Hardness: 3 to 15 dGH. It can thrive in soft water or moderately hard tap water.
Temperature: 64°F to 78°F (18°C - 26°C). It is a temperate to subtropical plant. It does not tolerate prolonged tropical heat (above 82°F) well, which can lead to melting. Conversely, it is cold-tolerant and can survive overwintering in ponds if the roots do not freeze.
Aquarium Lighting Requirements
Lighting is the single most critical factor for maintaining Myriophyllum aquaticum indoors.
Intensity: High to Very High. Without intense light, the internodes (distance between leaf whorls) elongate, making the plant look sparse and "leggy." Low light also causes the lower submersed leaves to shed.
Photoperiod: 8 to 10 hours of consistent light daily.
Spectrum: A full-spectrum light (5000K - 7000K) promotes the best growth. Red and blue spectrum peaks are beneficial for photosynthesis, but a daylight spectrum ensures the foliage appears natural green/blue-green.
Placement: The plant must be placed directly under the light source. Shading from hardscape or other plants will deteriorate its condition.
Substrate and Hardscape Preferences
Substrate: While the plant can absorb nutrients from the water column, rooting it in a nutrient-rich aquasoil yields the most robust stems. Sand or fine gravel can be used if root tabs are added. Inert, large-grain gravel is less ideal as it makes planting the delicate stems difficult.
Hardscape: This plant is best used to soften the edges of large stones or driftwood. Due to its rapid growth, it should be placed behind hardscape elements so it does not obscure them.
Fertilization and Nutrient Management
Myriophyllum aquaticum is a hungry plant that grows rapidly, depleting water column nutrients quickly.
Liquid Fertilization: A comprehensive liquid fertilizer containing both macro (NPK) and micronutrients is necessary. Lean dosing methods (limiting nutrients) are not recommended, as this plant will stunt and shed leaves.
Nitrates and Phosphates: It consumes high levels of nitrates and phosphates, making it excellent for controlling nutrient spikes in stocked tanks.
Iron (Fe): Regular iron dosing prevents the new shoot tips from turning pale or yellow (chlorosis).
Root Tabs: If using an inert substrate, replenish root tabs every 3 months to support the root system.
Tank Size, Planting, and Placement
Tank Size: Minimum 20 gallons, preferably larger. The vertical growth and spread of the plant can easily overwhelm nano aquariums (under 10 gallons).
Planting: Plant stems individually, leaving 1-2 cm of space between them. Bunching them too tightly restricts light and flow to the lower portions, causing rot. Use tweezers to insert the stem deep into the substrate to prevent it from floating up.
Placement:
Background: Due to its height, it is a classic background plant.
Floating: It can be left floating, where it will provide shade and cover for fish, though it may produce aerial roots that hang down, which some aquarists find unsightly.
Maintenance, Trimming, and Pruning
Maintenance is high for this species due to its aggressive growth rate.
Topping: When the stems reach the water surface, trim the top 4-6 inches. Replant these tops to replace older, leggier stems. This is the most effective way to keep the bush looking fresh.
Bottom Trimming: The bottom portions of the stems often deteriorate over time. Regularly pull up the old bottoms and discard them, replacing them with the healthy tops.
Thinning: If the bush becomes too dense, thin out stems to ensure light penetrates to the substrate. This prevents the "bare bottom" look common with Myriophyllum species.
Propagation Techniques
Propagation is strictly vegetative for this species in aquariums.
Stem Cuttings: Simply cut the stem at a node. The cutting can be replanted in the substrate or left to float. New roots will emerge from the nodes within days.
Side Shoots: Healthy plants will produce side shoots from the main stem. These can be snipped off and planted as independent stems.
Dry Start Method: Myriophyllum aquaticum is an excellent candidate for the Dry Start Method (DSM). Because its natural state involves emersed growth, it establishes roots quickly in wet soil with high humidity before the tank is flooded. During DSM, the leaves will take on their terrestrial, Waxy blue-green appearance.
Compatibility with Aquatic Species
Fish: Ideal for community tanks with Tetras, Rasboras, Guppies, and Gouramis. The dense foliage provides excellent hiding spots for fry and shy species.
Invertebrates: Safe for Neocaridina and Caridina shrimp. The fine leaves trap detritus and biofilm, providing a grazing surface for shrimp.
Snails: Generally snail-safe, though pest snails may use the dense leaves to hide eggs.
Plants: Combines well with broad-leaved plants like Anubias or Echinodorus for contrast. Avoid placing slow-growing, high-light plants (like carpeting species) directly under M. aquaticum, as it will quickly shade them out.
Common Cultivation Challenges and Troubleshooting
Symptom | Probable Cause | Solution |
Leggy growth / Long internodes | Insufficient Light | Increase light intensity or duration. |
Lower leaves turning brown/falling off | Self-shading or Low Light | Space stems further apart; trim and replant tops. |
Pale/Yellowing new growth | Iron Deficiency | Dose liquid iron supplements. |
Holes in leaves | Potassium Deficiency | Increase potassium dosage. |
Algae on leaves | Nutrient Imbalance / Low Flow | Improve water circulation; balance light and CO2; introduce algae eaters (Amano shrimp). |
Stems melting at soil line | Substrate Rot / Anaerobic conditions | Ensure substrate is not compacted; plant stems with spacing. |
Varieties and Cultivars
Variations of Myriophyllum aquaticum are limited compared to other aquarium species.
Standard: The most common form, characterized by green submersed leaves and blue-green emersed leaves.
'Dwarf': A smaller variant occasionally sold, though it often reverts to normal size under high nutrients.
'Red Stem': Some variants exhibit a reddish hue on the stem under extremely high light, but this is often a physiological response rather than a distinct cultivar.
Commercial Availability and Sourcing
Important Legal Warning: Myriophyllum aquaticum is classified as a prohibited invasive species in many jurisdictions, including parts of the United States (e.g., California, Washington, Minnesota), the United Kingdom, and the European Union. In these areas, the sale, transport, and possession of the plant are often illegal.
Where legal, it is commonly available in:
Local Fish Stores: Often sold in bunches as a pond plant or oxygenator.
Online Retailers: Available from aquatic nurseries, though reputable sellers will restrict shipping to banned states/countries.
Pond Supply Centers: Frequently sold alongside water lilies and hyacinths during the spring and summer.
Always check local Department of Natural Resources or Department of Agriculture regulations before purchasing or collecting this plant.
Conclusion
Myriophyllum aquaticum is a versatile and striking plant that bridges the gap between the aquarium and the water garden. Its unique texture and ability to grow both submersed and emersed make it a favorite for open-top aquariums and paludariums. While its care is relatively straightforward, success depends on providing high light and ample nutrients.
However, the aquarist must be responsible; its aggressive growth requires diligent maintenance, and its invasive potential demands strict adherence to local environmental laws to protect native waterways.
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