Hornwort (Ceratophyllum demersum), also known as Coontail, is a fast growing, aquatic flowering plant. It is commonly found in marshes, streams and lakes in North American and has been naturalized in parts of Europe. Many other regions – most notably Tasmania, consider hornwort an invasive species, and prohibit the possession or transportation of it.
Hornwort is easily one of the most popular aquarium plants and can be found in nearly any store that sells fish. It can adapt to almost any water type, and can tolerate a wide extreme of temperatures.
Because of its fast growing nature, many people use this plant to soak up nitrates in breeding tanks, or provide safe hiding places for fry in community fish tanks. When hornwort is allowed to float at the top of a fish tank, it provides a perfect refuge for tiny fry from hungry adult fish.
It it also often used in newly established fish tanks, or fish tanks with water quality problems. The fast growing plant will help balance out the water quality, and numerous fish tank crashes have been avoided by adding a large bunch of hornwort when there is an ammonia spike in an aquarium.
It should be mentioned that this plant is rarely used in showcase or highly visible fish tanks. It grows so quickly that it is difficult to aquascape with, and when planted, it has the unfortunate side effect of shedding needles like an old Christmas tree in the aquarium.
Hornwort thrives in a wide range of temperatures and in almost any lighting. Lighting should be kept on the low to medium side, and limited to about 8 hours a day. Any more than this, and the hornwort will take on a long stringy form, with large unsightly gaps between the needles.
It can be planted or allowed to float freely, but when planted the lower sections of the plant will often die. It does form a root like structure when placed in the substrate, but quickly starts to look terrible as it loses needles near the base of the plant. Because of this, it’s often easier to just let the plant float in the tank, and avoid planting it in the substrate all together.
Hornwort is incredibly easy to propagate. It will naturally grow side shoots off the main stem, and these can be pinched off to grow another full plant. Sections of the main stem can also be broken off, and both pieces will grow into full plants.
Hornwort is compatible with all fish, and is one of the few plants that will survive in a goldfish tank. That’s not to say that the goldfish won’t nibble on the plant, but it’s spiky nature and phenomenal growth rate, ensures that it will survive in a goldfish tank – as long as they aren’t too hungry.
It is also an excellent plant to have in live-bearer tanks, and as stated before – is a great refuge for baby fish. It provides a food source for the small fish (infusoria living on the plant needles), and the spiky needles generally keep the adult fish away from the baby fish.