Hornwort

Overview

Hornwort (Ceratophyllum demersum) is a fast, rootless stem plant and one of the best natural tools for beating algae. Its bristly, forked stems grow explosively, soaking up nitrate and phosphate faster than almost anything else and shading and sheltering fry and shrimp. It tolerates a huge temperature range (coldwater to tropical), needs no CO2 and no substrate, and asks for almost nothing — making it a favourite emergency plant for new or algae-troubled tanks.

Planting & placement

Hornwort has no true roots, so it is happiest floating, absorbing nutrients along its entire length. You can weigh the base down or bury a stem in the substrate for a bushy background, but the buried section tends to rot and shed, so floating (or loosely anchored) is usually best. Floating clumps give fantastic cover for fry and dim the light for shade-loving plants below. See aquascaping for beginners for using floaters.

Light, CO2 & ferts

Hornwort is unfussy about light, growing from low to high — more light just means faster growth. It needs no CO2. Because it grows so fast it is a heavy feeder, drawing nutrients straight from the water, so a complete liquid fertilizer keeps it from stripping the tank and going pale. No root feeding is needed since it has no roots.

Propagation & problems

Propagation is effortless: just split it. Snap or cut off any length of stem and it carries on growing as a new plant — no roots or planting required. Trim constantly to stop it overrunning the tank. The main problem is needle shedding after a shock or from a buried, dying stem base; keep conditions stable and float it to minimise mess. For another fast nutrient sponge, see water wisteria. Its wide temperature tolerance makes hornwort one of the few plants equally at home in an unheated coldwater or goldfish tank and a tropical one. Trim and thin it regularly, and use the offcuts to plant other tanks or hand to fellow hobbyists — you will never be short of it.