TankBud

Duckweed

Lemna minor

Also known as Common duckweed, Lesser duckweed, Least duckweed

FreshwaterFloatingSide shoots

Duckweed (Lemna minor)
Kostka Martin · CC0

Care at a glance

Light
Low light
CO2
No CO₂ needed
Temperature
59–86°F
15–30°C
Max height
0.4 in
1 cm
Growth rate
Fast
Placement
Floating
Type
Floating
pH
6.0–8.0
Hardness
2–20 dGH
Spread
11.8 in (30 cm)
Nutrient uptake
Water column
Growth region
Submersed or emersed
Difficulty
Beginner
Family
Lemnaceae
Origin
Nearly cosmopolitan; native across temperate and tropical regions of Europe, Asia, Africa, and the Americas

Overview

Duckweed is about the easiest floating plant there is, and it fits the Walstad and low-tech approach well. Keepers use it for nutrient export, for shade and to calm shy or surface-dwelling fish.

Did you know

Duckweed absorbs ammonium roughly 3 to 11 times faster than nitrate. A duckweed mat can strip a fresh dose of fish waste out of the water almost as quickly as the biofilter can process it.

Caring for duckweed

Float duckweed on the surface, since it needs no substrate. It draws nitrate, ammonium and phosphate straight from the water column, so any fertilizer should go in as a liquid.

It grows fast under even modest light and needs no CO2. It takes 59 to 86°F (15 to 30°C).

It multiplies explosively, and it clings to nets and hands. Plan to skim off handfuls every week. Once it is established, it is very hard to remove completely.

Good to know

Duckweed, Lemna minor, belongs to the family Lemnaceae, which is increasingly folded into the arum family Araceae. The family contains the smallest flowering plants on Earth. The visible green body is a frond, a reduced fusion of leaf and stem. It flowers only rarely and inconspicuously, and it reproduces almost entirely by budding off new fronds. Regulators such as the US EPA use it as a standard test organism for water toxicity, since its growth is highly sensitive to contaminants.

In the wild

Common duckweed is a near-cosmopolitan floating plant of still and slow-moving fresh water. It is found almost everywhere except the coldest and driest regions. Each plant is a single flat oval frond only a few millimeters across, with one hanging rootlet. Colonies quickly carpet the surface of ponds, ditches and quiet backwaters. In cold climates it survives winter as starch-filled fronds called turions, which sink to the bottom.

Common questions

Does duckweed need to be planted in the substrate?

No. Duckweed floats at the surface and takes its nutrients straight from the water.

Does duckweed need CO2?

No. Duckweed grows well without added CO2 and suits a low-tech tank.

How much light does duckweed need?

Duckweed is a low-light plant, and the light that comes with a standard tank kit is enough for it.

How do you propagate duckweed?

Duckweed propagates by side shoots. Side shoots bud off and float free.

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