Duckweed
Lemna minor
Also known asCommon duckweed · Lesser duckweed
Water parameters
Light and nutrients
Substrate type: floating. Propagation: fragmentation.
Substrate compatibility
| Substrate | pH effect | Nutrient load |
|---|---|---|
| Bare bottom (no substrate) (Bare bottom) | n/a | none |
| Inert sand (Pool filter sand) | neutral / inert | none |
| Inert gravel (Aquarium gravel) | neutral / inert | none |
| Aquasoil (ADA Amazonia) | lowers pH | very high |
| Mineralized clay substrate (Seachem Fluorite) | neutral / inert | moderate |
| Dirted tank (mineralized topsoil) (DIY soil substrate) | slightly acidic | very high |
| Wood and rock mounts (Hardscape mount) | varies | none |
With fish
Origin and habitat
A tiny free-floating plant found through most of the temperate and tropical world, native across Africa, Asia, Europe and North America and naturalised in Australasia and South America. Long placed in its own family Lemnaceae, the duckweeds are now treated as the subfamily Lemnoideae within the arum family Araceae, a group of about 36 species in five genera, Spirodela, Landoltia, Lemna, Wolffia and Wolffiella, which includes the smallest flowering plants on earth, the Wolffia species under a millimetre across. Common duckweed, Lemna minor, is a little larger, each frond a flat green disc 1–5 mm wide with one trailing root, drifting on still ponds, ditches, marshes and quiet backwaters. Growth is explosive: each frond buds daughters continuously, and in warm, nutrient-rich, well-lit water a population can double its mass in as little as a day or two. That runaway growth is its defining trait and the root of both its usefulness and its bad reputation.
Outdoor pond use
- USDA zones
- 4–13 (winter low around -34°C or warmer)
Care notes
The fastest-growing aquatic plant in the hobby and a divisive one. Many value it for stripping ammonia, nitrate and phosphate from the water, for live food for herbivorous fish and shrimp, and for shade; others can never be rid of it, since a single overlooked frond restarts the whole population through water changes, net sweeps, even a full teardown. In aquaponics it is genuinely useful as a supplemental feed: dried duckweed runs about 25 to 45 percent protein, it grows continuously, and it can be skimmed and fed to tilapia, carp, koi and goldfish, with studies showing improved growth when it replaces part of a tilapia ration. Demands are minimal, any light above dim, temperatures from about 5°C to 35°C, and almost any water chemistry, with growth fastest in warm, nutrient-rich, still water under strong light. Surface flow from filters slows it and shoves it into corners, while still water lets it carpet the surface, so the main job is harvesting, skimming the excess a few times a week to keep it from blocking light to plants below. It is genuinely aquaponics- and hydroponics-suitable as a fast nitrogen-stripping, harvestable feed crop.