Giant Duckweed
Spirodela polyrhiza
Synonyms Greater duckweed
Giant Duckweed (Spirodela polyrhiza) is a floating plant for the surface, growing to about 0.5 cm (0.2 in) at a fast pace. It wants 50–86°F (10–30°C), low light and no CO₂, and counts as an easy plant to keep alive.
At a glance
| Type | Floating plant |
|---|---|
| Light | LowThe least light it survives in, not the light it looks best in. |
| CO₂ | Not neededWhether it survives without added CO₂ — not whether CO₂ would help it grow faster. |
| Difficulty | Easy |
| Temperature | 50–86°F (10–30°C) |
| Max height | 0.5 cm (0.2 in)Grown submersed, left to mature, never trimmed. |
| Growth rate | Fast |
| Placement | floating |
| pH | 6–8.5 |
Before it goes in
- Giant Duckweed lives under a plain low-light LED — it does not need a planted-tank lamp to survive.
- It grows without CO₂.
- It stays around 0.5 cm (0.2 in), low enough to keep the front glass clear.
- Its leaves are medium: Goldfish, Electric Yellow Lab and Colombian Ramshorn Snail will eat it.
Can it grow without CO₂?
Yes. Giant Duckweed does not need CO₂ at all.
How much light does it need?
Low light is enough — and that is the survival line, not the “it looks better” line.
How big does it get?
About 0.5 cm (0.2 in) tall when it is mature and untrimmed, growing fast, and it does not root at all.
Will my fish eat it?
Its leaves are medium, so some will: Goldfish, Electric Yellow Lab and Colombian Ramshorn Snail.
What it goes with
- Plants that run on the same light and CO₂, so they can share a tank without one of them being the odd one out: Hygrophila corymbosa 'Siamensis', Anubias nana 'Petite', Cryptocoryne wendtii and Hygrophila corymbosa 'Compact'.
- Animals that share its temperature range and will not eat or uproot it: Betta, Cherry Shrimp, Angelfish and Bristlenose Pleco.
Often compared with
More plants
Sources (2) · checked Sep 2026
- Light, Root feedingtropica.com
- Max heightflowgrow.de