Vallisneria spiralis is a substrate-rooted aquatic plant (non-floating) with fibrous root structure and is known also as straight Vallisneria, tape grass, eelgrass, or most commonly as eelweed. It is a very commonly-used aquarium plant and is actually one of the first plants used in aquaria back in the late 19th century.
Eelweed is globally distributed in tropical and subtropical regions, primarily being introduced through contaminated shipping containers, ship ballast water discharge upon entering and exiting the port, and accidental release from aquaria. The plant is considered a native species in Egypt, Sudan, The Congo, India, Iraq, southwest Asia, Italy, and Hungary.
Vallisneria spiralis has long, narrow, linear leaves with 3-5 parallel leaf veins that can be colored from pale green to reddish in hue. Leaf margins can be entire to finely toothed, depending on the variety.
Fully-grown, mature plants of some varieties can be up to 1 meter in size.
Vallisneria spiralis is a dioecious plant, meaning that there are plants with only male flowers and other plants with only female flowers. Some members of the genus Vallisneria are monoecious (plants have both male and female reproductive parts on separate stalks), whereas other members have perfect flowers, producing both male and female reproductive parts in the same flower.
Flowers are produced on long spiral-shaped stalks that are shed when mature and float to the surface of the water. Aquarium reproduction is typically asexual and occurs by runner propagation. To date, no sexual reproduction has been observed in aquaria, likely due to a lack in the presence of unrecognized environmental stimuli.
Eelweed is considered an invasive plant in some locations, such as New Zealand, and possession or transport of eelweed is banned. In Iceland, Vallisneria spiralis is found growing in warm geothermal pools and is regarded as a “naturalized alien”, meaning that its presence has so long been established that it is now considered native to Iceland despite not originating from the island.
Benefits of Eelweed
Nearly all species of fish, as well as their fry, will benefit from both the water chemistry stabilizing contributions of eelweed and the cover it provides. Cover for fish is a very good means of reducing tank stress for all your aquatic animals.
If you host digging fish that like to burrow into the aquarium substrate, these fish can disturb the root systems of Vallisneria spiralis and cause growth stunting and yellowing, so please be advised of this when selecting species for your tank.
Snails are very fond of eelweed and will spend most of their time crawling along its leaves, grooming the plants from surface algae growth.
How to care for Vallisneria spiralis
Eelweed is a hearty plant that is a good choice for beginner aquarists who want to establish a planted freshwater tank. There are several commercially-available varieties that can be purchased at aquarium shops and nurseries that cultivate aquatic plants.
One cultivar, Tiger (a variant of Nana), is a shorter variety of eelweed that is appropriate for smaller aquariums. Its leaves only grow to about 30-50 cm when mature and will not tend to take over the tank too quickly. Tiger forms many runners and is basically effortless to propagate, so starting with just one or a few plants and allowing them time to acclimate to the tank conditions will eventually yield a full tank of Vallisneria.
Other popular varieties of eelweed include Americana, Gigantea, Asiatica, Biwaensis, and Nana.
Eelweed grows quite well in tanks with low lighting conditions. So if you choose fish for your tank that prefer lower light levels, eelweed is a good choice for establishing a planted tank. Water condition tolerances for Vallisneria spiralis are broad and the plant will readily grow in water of pH 6-9.
Eelweed is also very temperature-tolerant and can grow in cooler (16°C) or warmer (30°C) tank conditions. Essentially, Vallisneria spiralis cultivation in your aquarium is virtually idiot-proof.
Vallisneria spiralis prefers tank substrates that are either sandy loams or clay loams, which means that just about any soil substrate, with exception to clays and sands, that you would grow garden plants in will do.
Starting with a single eelweed plant under favorable conditions (which, as we said, are rather broad) can yield up to 50 new plants after one year. If you attempt to thin out the eelweed growth by removing young plants and wish to transplant them to another tank, wait until the plants have 3-4 developed leaves and are about 6-8 cm in size.
This will allow the young plants to develop to a growth stage where they will be tolerant of transplantation and can readily re-adapt to a new tank.
To maintain workable levels of eelweed growth, it is not recommended that you trim its leaves since it does not respond well to pruning damage and the cut leaves will quickly yellow, decay, and promote bacterial and algal growth in the tank. Instead, carefully separate portions of the base of the eelweed at the root bulb and remove the excess plant material, paying special attention to preserving the root structure.
As an added caution, if you do have an algae problem at some point in your aquarium and require exogenous chemical controls, be aware that many algae treatment agents contain copper as an algal toxin and will damage the eelweed plant.
Eelweed will grow vigorously if your aquarium uses a carbon dioxide injection system, however, this addition to your tank is not necessarily good for Vallniseria growth. As with other aquatic plants, eelweed will also grow more productively with the addition of liquid fertilizers.
Just be careful to follow the directions on the bottle, add only the recommended amount for the size of your tank, and be sure to monitor the nitrate and phosphate levels after fertilizer addition to ensure the tank chemistry is within healthy parameters.