How many oxygenating plants in a pond? The right amount, the right species, and common misconceptions

“You need oxygenating plants.” That is the advice every new pond owner receives. But how many? Are two bunches enough for a 5 m³ pond? Should they be planted everywhere? And do they really oxygenate the water? Oxygenating plants are above all formidable competitors to algae: their real role is to absorb nutrients before algae can, much more than to provide oxygen. Here is the right dosage and the species to prioritize.

What oxygenating plants really do

Their name is somewhat misleading. Yes, they release oxygen directly into the water during the day through photosynthesis: in bright sunshine, you can sometimes see fine bubbles forming on their leaves. But at night, they respire like all living things and consume oxygen. Over 24 hours, their oxygen balance is positive, but they do not protect against the dawn dip that threatens fish in summer.

Their real strengths lie elsewhere:

• They absorb nitrates and phosphates directly from the water through their leaves, thereby depriving algae of their food. This is the most powerful mechanism against green water and filamentous algae.
• They shelter life: fry, insect larvae, and beneficial microorganisms.
• They provide spawning support for goldfish and koi.
• Their surfaces host bacteria that help purify the water.

The right dosage

These figures are guidelines based on our experience, for getting started. Oxygenating plants grow quickly: the goal is not to add many on the first day, but enough for them to become established before the algae. Ultimately, aim for submerged plants occupying approximately one-third of the water volume, and surface coverage (water lilies, floating plants) of 50 to 60%.

In a koi pond, allow for more plants or protect them: koi readily graze on tender plants. A mesh basket or a separate shallow area gives them time to develop.

Which species should you choose?

• Coontail (Ceratophyllum demersum): rootless, it floats beneath the surface, grows quickly and overwinters at the bottom. Highly effective.
• Eurasian watermilfoil (Myriophyllum spicatum): fine foliage, excellent spawning substrate.
• Pondweeds (Potamogeton): broader leaves, very hardy.
• Mare's-tail: submerged to semi-emergent, decorative.
• Water-starwort: for cool, shallow water.

To avoid: several plants long sold as “oxygenating” plants are now listed as invasive alien species under the European list, and both their sale and planting are prohibited. This notably applies to lagarosiphon (Lagarosiphon major), Nuttall's waterweed (Elodea nuttallii), parrot feather (Myriophyllum aquaticum) and Carolina fanwort (Cabomba caroliniana).

How and when to plant them

1. In spring, as soon as the water exceeds 10 to 12 °C, so they can become established before the algae surge. Planting at the beginning of autumn is still possible for hardy species, but their effect will not be felt until the following spring.
2. Weight down the bundles with a small lead clip or plant them in a basket filled with gravel, at a depth of 30 cm to 1 m.
3. Coontail is simply placed in the water: it does not need to be planted.
4. Distribute them in several groups rather than a single clump.
5. Prune in summer if they take over everything: regularly removing part of the mass also removes from the pond the nutrients they have absorbed.

Read also

Discover our list of oxygenating plants for ponds and water gardens

READ THE ARTICLE

Frequently asked questions

— Are oxygenating plants enough to oxygenate a fish pond?

No. They produce oxygen during the day but consume it at night. In a pond with fish, especially koi, a pump or aerator remains necessary in summer.

— Can you add too many oxygenating plants?

Yes: a completely overgrown pond loses water circulation and can experience significant nighttime oxygen dips. Prune them as soon as they occupy more than half the volume.

— My koi eat my oxygenating plants. What should I do?

Protect them in mesh baskets, create a separate shallow area or choose hardier species. Koi remain grazers: tender plants do not last long in the open.

— Can oxygenating plants be planted in autumn?

It is possible with hardy species, but they grow little before winter. Spring remains the best time for them to compete with algae from the start of the season.

In summary

• 3 to 5 bunches per m² of surface area to start, one third of the volume once established.
• Their strength: capturing nutrients before algae do.
• Native species only, never prohibited invasive alien species.
• They do not replace aeration in a fish pond.

Last updated: September 28, 2026.