Waterweed, Elodea – in the pond and care in the aquarium

Although waterweed belongs to the frogbite family, it presents itself in a clearly divergent habit. The flexible stems are densely covered with rounded or oblong leaves, which – depending on the species – are up to 3 cm long. In standing water, the long, heavily branched shoots reach a length of up to 3 meters. Only the tiny, white flowers appear on the water surface, provided the waterweed forms a flower at all. All green parts of the plant thrive underwater, appearing in ever new shades of color and changing to brownish during the winter. At the bottom of the body of water, elodea take root only to a minimal extent. Most of the roots sprout from the nodes of the stems and side shoots.

species in Europe

About 10 species are known worldwide, 3 of which have established themselves in Central Europe. These can be found in the wild in many standing or slow-flowing bodies of water, such as reservoirs and quarry ponds, ponds, moats or rivers.

Canadian waterweed (Elodea canadensis)

• whorled, dark green leaves
• produces exclusively female flowers from May to August
• compact growth habit with sprouts up to 100 cm long

Narrow-leaved waterweed (Elodea nuttallii)

• narrow, reflexed, curled leaves
• Stems are overgrown unevenly
• tiny flowers up to 3 mm high

Argentine waterweed (Elodea callitrichoides)

• long, pointed leaves hang limp on the shoot
• very rare, white flowers from May to August
• not fully hardy

All presented Elodea species are well suited for cultivation in ponds or aquariums.

maintenance in the pond

In contrast to a large number of pond plants, such as the native floating plants, the waterweed is not under nature protection. Hobby gardeners who want to settle Elodea in their own water world can cut off the sprouts from a plant in the wild without a guilty conscience and transport them in a water-filled plastic container. The waterweed is so vigorous that even a small piece of a shoot without roots is enough to create an underwater forest in a short time. Of course, specialist retailers have the robust aquatic plant available for garden enthusiasts to buy almost all year round.

• Stick a piece of plant in the bottom of the pond or just lay it on the water.
• Waterweed needs a sunny to partially shaded position.
• Ideally, the water quality is clear and clean.
• Elodea also thrives in cloudy, slightly polluted pond water.
• Fertilizer is only used when there are signs of deficiency.
• Special fertilizer for pond plants in liquid form is suitable.
• Regular trimming and thinning of the stems limits spread.

If there are other underwater plants in the pond, there is a risk that they will be overgrown by waterweed. The experienced gardener prevents this situation by using these plants in a plant basket. From time to time he pulls out the baskets and removes any overgrowth caused by the waterweed by simply pulling out the unwanted parts of the plant.

hibernate

With the exception of the Argentine waterweed, the other Elodea species are fully hardy. The shoots turn brown and sink to the ground. If the pond does not completely freeze over in winter, new shoots appear from early spring and rise towards the water surface.

Since the dead shoots no longer contribute to the oxygen supply, they threaten to pollute the water quality in winter due to rot. As a result, the experienced gardener fishes off a large part of the underwater forest in autumn as a prophylaxis. The vigorous waterweed is not affected in this way, but continues to thrive in the next season. Most of their biomass goes dormant and turns brown; however, some winter buds remain at the bottom of the pond, from which the elodea will re-spread in spring.

In regions with mild winters, the evergreen Argentine waterweed has a good chance of surviving the cold season in good health. Where frost-intensive winter periods are expected, it is advisable to place the plant so that it is deep enough in the water so that it does not fall victim to the first frost. Because it does not go dormant like the other Elodea species, this species needs light at all times of the year. If a thick sheet of ice closes over it while the water temperature does not constantly exceed 4° Celsius, Argentine waterweed dies.

Care in the aquarium

Among the plants for the aquarium, waterweed is one of the classics. It brings fullness to the appearance, keeps the water free of algae due to the high nutrient consumption and serves the living beings as:

• retreat
• Ablaichplatz
• food
• oxygen supplier

Experienced aquarists use Elodea as a background plant because its rapid growth would quickly obscure the colorful aquatic world. It is the industrious willingness to grow that makes maintenance a little more complex in the narrow space of the aquarium than in the garden pond.

Plant or let it drift

Once the decision has been made to integrate the waterweed in the aquarium, there are two options to choose from:

Plant using the traditional method

• Defoliate the ends of several stems over a short stretch.
• Only plant the leafless shoots.
• Make sure the waterweed is in the background.

Let Elodea float

• Useful for cultivation in bottomless breeding tanks.
• Simply lay out the young plant on the water surface.

Elodea floating loosely on the water surface are rather unsuitable for aquariums that are designed according to a formal structure. On the one hand, the plant will constantly try to root itself in the ground like in a garden pond. In addition, excessive shading of the other plants could occur, which has a detrimental effect on their growth.

The right lighting

In the wild, the sun provides the plants with the vital supply of light. Artificial light sources are sometimes required in the aquarium, the intensity of which must be carefully dosed so that the waterweed thrives optimally.

• A need-based light intensity promotes leaf growth on the stems.
• In the bright location, the waterweed is content with the indirect amount of light.
• If there is a lack of light, LED, T5 or T8 lamps are also used for hourly lighting.
• Direct sunlight on the aquarium should be avoided at all costs.

So that the lamp shape can be adapted to the home furnishings, aquarium lighting can be purchased in various designs, such as hanging lights, spotlights or surface-mounted lights.

The professional substrate

An essential prerequisite for healthy plant growth in the aquarium is the condition of the soil, which should come as close as possible to the natural specifications. Although waterweed is quite flexible with temperatures, it fares poorly when cultivated in an aquarium that has a tropical warmth at the top and room temperature at the bottom due to a rod heater.

• Use floor heating with integrated floor flow in the aquarium.
• Uniform temperatures and water movements are created.
• At the same time, the waterweed is better supplied with nutrients.
• Apply only specific mixtures from specialist shops as soil substrate.

Aquaristic beginners in particular tend to use pond soil or even potting soil as substrate. Since the conditions in the tightly limited environment of an aquarium are completely different, this decision can prove fatal. Not only for waterweed, but for all other plants in the aquarium, it is better to use professional substrate from the start, based on nature’s example, with quartz sand and clay minerals.

Fertilize

If the waterweed loses its rich green color and keeps getting lighter, it is not doing well. If the other environmental conditions in the aquarium are within normal parameters, the suspicion arises that there is an undersupply of nutrients. As in the garden pond, the aquarist only uses a fertilizer when there are indications of malnutrition in the waterweed.

• Do not use commercial garden or flower fertilizers.
• The calcium, magnesium and nitrate it contains is already contained in tap water.
• Modern aquarium fertilizers are correctly dosed and water-soluble over a long period of time.

In order to prevent over-fertilization, which would immediately open the door to an algal bloom, experienced aquarium operators use a daily fertilizer that ensures a sufficient supply over 24 hours and whose administration can be stopped as soon as the deficiency symptoms of Elodea species disappear.

CO2 supply

Plants in the wild take the most important nutrient for their growth, carbon, from the air. Since waterweed in the aquarium only the CO2 dissolved in the water is available, this supply is quickly used up due to the spatial confinement. In the worst case, the chemical administration of carbon causes an increase in pH up to the upper, alkaline regions, which is not good for waterweed or other plants and creatures. Consequently, only the gaseous administration of CO2 comes into question for foresighted aquarists. For this purpose, a suitable device is available in specialist shops for every volume, from the inexpensive starter set to the fully automatic professional system, which constantly measures the CO2 content and releases the carbon if necessary.

The amount of CO2 required in the water depends on various factors, such as plant density or fish stocks. Experience has shown that the value should not fall below 5 mg per liter of water and ideally range between 10 mg and 20 mg per liter.

Conclusion
Despite its invasive character, waterweed should not be missing in any pond or aquarium. Their valuable contribution to maintaining or improving water quality and as an impressive oxygen supplier clearly outweighs their disadvantages. By regularly trimming and thinning out the underwater forest, pond owners and aquarists keep the rampant Elodea in check. When cultivating in the garden pond, the hobby gardener is forced to react to external influences. In the aquarium, it actively influences growth through the use of artificial lighting, targeted administration of CO2, use of floor heating and floor flow, and a species-appropriate substrate.