Ceratophyllum Demersum / Hornwort

Quick facts

Identity

Also known as

Coontail; Rigid hornwort; Coon's tail

Synonyms

Ceratophyllum demersum var. apiculatum; Ceratophyllum demersum var. inerme

Environment

Freshwater

Native to

Cosmopolitan, native to every continent except Antarctica

Habitat

Quiet or slow-flowing lakes, ponds, ditches, canals, and streams with nutrient-rich to eutrophic water

Sourcing

Aquacultured

Conservation

Not Evaluated

Care

Care level

Easy

Growth form

Stem

Max height

4 – 78 in (10 – 198 cm)

Spread

24 in (61 cm)

Growth rate

Fast

Placement

Midground, Background, Floating

Water

Temperature

59 – 86 °F (15 – 30 °C)

pH

6.0 – 8.5

GH

3 – 18 dGH

PAR

20 – 50 PAR

Flow

Low

Light

Low

CO₂

Not needed

Planting

Substrate

Not needed

Feeds from

Water column

Fertilizer needs

Low

Colors

Green

Feeding & breeding

Propagation

Cuttings

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Care guide

Overview

Hornwort is a rootless stem plant sold as loose sprigs or bunches, identified by its whorls of fine, needle-like dark green leaves along branching stems. It can float at the surface or be anchored in the mid or background, growing fast enough to need trimming every week or two. Its rapid nutrient uptake and detritus-trapping tangle make it popular for fry and shrimp tanks, though shed needles can cloud water after handling.

Care

Hornwort tolerates almost any water chemistry and lighting level, which makes it forgiving for new fishkeepers setting up their first planted or fry-rearing tank. It can be left to float at the surface, where it grows fastest and shades the water below, or weighted down with plant lead or tied to a hardscape piece in the mid or back of the layout. Regular trimming is necessary since growth is rapid and untrimmed stems quickly shade out everything beneath them. Unlike most stem plants it has no true roots, so it draws nutrients directly through its foliage from the water column.

Planting & trimming

No true roots are formed, so hornwort can simply be left loose to float at the surface or anchored with a plant weight, gravel, or by tucking stems under a rock or driftwood. It does not need to be buried and will not root even if pushed into substrate. Trim the stems every one to two weeks to control size and replant or discard the cut portions, since untrimmed growth quickly overtakes a tank.

Fertilizing

Because the plant absorbs nutrients through its leaves rather than roots, root tabs are of no use and liquid or water-column fertilization is the only practical option. It grows well even in low-nutrient tanks, but in heavily stocked, nutrient-rich water its uptake rate increases noticeably and it can outcompete algae for nitrate and phosphate. Pale or thinning foliage toward the base of older stems usually just reflects self-shading rather than a nutrient deficiency, and is remedied by trimming and replanting the healthier tops.

Propagation

Propagation is by stem cuttings: any healthy side shoot or trimmed top section will continue growing on its own when left floating or lightly anchored. Broken fragments from an established plant also readily form new growth, which is part of why it spreads so easily in the wild. In temperate outdoor ponds it additionally produces turions, or winter buds, that sink and overwinter before regrowing in spring.

Problems

The main problem keepers encounter is shedding of the fine needle-like leaves when the plant is moved, handled roughly, or exposed to a sudden change in light or water chemistry, which can cloud the water and clog filters temporarily. Because it grows so quickly it can also become a tangled mass that traps detritus and blocks light to other plants if not thinned regularly. It is naturally resistant to most algae issues since it releases compounds that inhibit phytoplankton and cyanobacteria growth.

Sources

1. Ceratophyllum demersum - Wikipedia
2. Hornwort (Ceratophyllum demersum) - Scale & Stem
3. Ceratophyllum demersum - Rigid hornwort - Flowgrow Aquatic Plant Database
4. Hornwort – Ceratophyllum demersum care guide | Aquairi

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