Ceratophyllum demersum, commonly known as Hornwort, is a popular submerged aquatic plant used in freshwater aquariums and ponds. This species is unique because it is entirely rootless, absorbing all necessary nutrients directly from the water column. Hornwort is known for its vigorous and fast growth, making it an effective natural filter.
Quantifying Hornwort’s Growth Rate
Hornwort’s growth speed varies significantly by environment, but under typical aquarium conditions, it exhibits a rapid rate of increase. A healthy stem can gain between 1 to 4 inches (3 to 10 cm) of length per week. This continuous elongation means the plant can quickly reach the water surface and spread horizontally in a standard tank.
In high-demand environments, such as those with CO2 injection and high light, the growth rate can be explosive. Hobbyists have reported observing growth of up to six inches per day or three feet of total stem growth per week under optimized conditions. This rapid proliferation means biomass doubling can occur in as little as two weeks when environmental factors are maximized. This speed allows the plant to efficiently outcompete most forms of algae for available nutrients.
Controlling Factors That Influence Speed
The primary factors controlling Hornwort’s growth speed are light, temperature, and nutrient availability. Manipulating these factors is the most effective way to accelerate or slow the plant’s development to suit a specific aquatic setup.
Light
Light intensity directly correlates with photosynthetic activity and growth acceleration. The plant performs best under moderate to high light levels, requiring a photoperiod of 8 to 10 hours daily for dense growth. If the plant receives too little light, it becomes “leggy,” stretching its stem with sparse foliage as it attempts to reach a brighter area. Conversely, excessive light can cause the plant to shed its needle-like leaves, especially if not balanced with sufficient nutrient levels.
Temperature
Hornwort is highly adaptable, thriving across a broad temperature range that supports both tropical and cold-water environments. The most vigorous growth occurs when the water temperature is maintained between 59°F and 86°F (15°C to 30°C). Temperatures outside this optimal spectrum cause a slowdown in metabolic activity and growth rate. Growth becomes sluggish in cooler water, demonstrating that thermal energy is a strong accelerator.
Nutrients and CO2
As a rootless species, Hornwort is a dedicated water column feeder with a high demand for macronutrients like nitrogen and phosphorus. The availability of these compounds, often in the form of nitrates and phosphates from fish waste, directly dictates its growth speed. If the water is nutrient-rich, the plant grows quickly, acting as a natural filtration system. While Hornwort does not require supplemental CO2, providing it will dramatically accelerate growth, causing the plant to grow denser and more robustly by boosting carbon uptake.
Managing and Utilizing Rapid Growth
The plant’s rapid growth necessitates regular intervention to maintain a balanced aquatic environment. The primary control method is mechanical removal, or pruning, which must be performed frequently.
Pruning Techniques
Pruning Hornwort is straightforward, involving snipping the stems at the desired length with scissors or by hand. Because any fragment can grow into a new stem, cuttings can be used for propagation or must be removed entirely. Regular trimming is necessary to control the plant’s size and to encourage side shoots, resulting in a bushier, denser appearance.
Anchoring vs. Floating
Hornwort is naturally a free-floating plant, and allowing it to drift near the surface maximizes its growth speed due to optimal access to light and atmospheric carbon dioxide. While it can be anchored to the substrate using plant weights or by wedging the base into hardscape, the submerged end of the stem often begins to rot. This decay occurs because the plant lacks roots and the buried portion is cut off from the light needed to maintain stem health.
Responsible Disposal
Given Hornwort’s invasive potential in non-native environments, responsible disposal of trimmings is necessary for all aquarists and pond owners. Flushing cuttings or tossing them into the yard can lead to their introduction into local waterways, where they can outcompete native species. The correct procedure is to dry the plant material completely, often by placing trimmings in a sealed bag or bucket for a few days, before disposing of the dead, desiccated matter in the household trash.