Plants in an aquarium are more than decoration. They take nitrate and phosphate out of the water, give cover to fry and shy fish, damp the flow and take up space that algae would otherwise claim. A planted tank forgives more mistakes than a bare one.
But a plant is a tank inhabitant with needs of its own. Choose it not by how it looks in a photo, but by three things: light, substrate, neighbours.
Plants that need no substrate
Some species do not root in the substrate at all. They are tied to a rock or a piece of driftwood with fishing line, or glued in place, and the roots attach themselves to the surface. This is the only option for tanks with a rocky bottom, strong flow, or fish that dig.
- Anubias (Anubias barteri and its forms, Anubias nana) — a tough leaf, slow growth, tolerant of low light.
- Java fern (Microsorum pteropus) and its varieties — undemanding, reproducing by daughter plants straight off the leaf.
- Bucephalandra — varied and attractive, but needs more stable water and good flow.
- Mosses — java, Christmas, flame: they hold onto any surface and shelter fry and shrimp.
One rule matters: with anubias and ferns the rhizome must not be buried — it will rot. Only the roots go into the substrate; the rhizome itself stays on the surface.
Plants for strong flow
Mountain streams carry almost no vegetation, and a tank with strong flow is planted just as sparsely. The same attaching species stand up to the current — anubias, java fern, mosses, bucephalandra — along with the stiff-leaved bolbitis. All of them are fastened to rocks and wood rather than planted: strong flow washes plantings out within a week.
Plants with soft, finely divided leaves (cabomba, hornwort, limnophila) are torn apart in such tanks.
Plants with herbivorous fish
Large characins, many cichlids, silver dollars and headstanders strip soft greenery within days. Plants with a tough, dense, unappetising leaf stand a chance:
- anubias — the most reliable option;
- java fern and bolbitis;
- firm-leaved cryptocorynes — sometimes they survive, sometimes not;
- large echinodorus — they hold out when the fish is well fed with plant food.
A simple measure: if the fish eats plants, feed it plant food — blanched courgette, cucumber, spinach, spirulina tablets. A hungry herbivore will eat anything.
Plants for low light
For tanks without powerful lighting: anubias, cryptocorynes, java fern, mosses, vallisneria, dwarf hygrophila. Demanding carpeting species and red plants stretch, fade and grow algae without strong light and added CO₂.
Floating plants
Water lettuce, frogbit, riccia, salvinia and duckweed give shade and cover at the surface. That is exactly what labyrinth fish, bettas, dwarf cichlids and any shy species need. They grow fast and pull nitrogen out of the water, which helps against algae outbreaks. There is one drawback: they spread and shade everything below, so they have to be thinned regularly.
Floating plants do badly with condensation from a splashing filter and with a tightly closed lid.
What the plants themselves need
- Light — 8–10 hours a day, with no "extra just in case". A longer day produces algae, not growth.
- Nutrients. Nitrogen and phosphorus come from fish waste, but potassium and trace elements are usually short in an aquarium and are added as fertiliser. Root feeders (cryptocorynes, echinodorus) want root tabs.
- Substrate — a 2–4 mm grain for rooting species. Roots will not hold in coarse gravel and suffocate in very fine sand.
- Stability. Plants react to parameter swings more slowly than fish, but they also take longer to recover.
Common mistakes
- Burying the rhizome of an anubias or a fern — the commonest way to kill them.
- Plants from an outdoor pond. Parasites, hydra and pest snails come in with them; the source is not a safe one.
- Abrupt changes of light and fertilisation. Algae respond to change faster than higher plants and take the space that opens up.
- Plants in a tank under treatment. Many medications suppress plants, and copper-based ones are lethal to invertebrates.