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
Found on every continent except Antarctica. The family Lemnaceae includes several genera (Lemna, Spirodela, Wolffia) collectively called duckweed. The most common aquarium and aquaponics species is Lemna minor. These are the smallest flowering plants in the world; individual fronds are 1–5 mm across, consisting of a single flat green disc with one or more trailing roots. Duckweed floats on still or slow-moving water surfaces of ponds, ditches, marshes, and quiet river backwaters. Growth is exponential under favorable conditions: each frond buds daughter fronds continuously, and a population can double in mass every 2-3 days in warm, nutrient-rich water with good light. This explosive growth rate is the plant's defining characteristic and the source of both its utility and its infamy in aquarium keeping.
Outdoor pond use
- USDA zones
- 4–13 (winter low around -34°C or warmer)
Care notes
The fastest-growing aquatic plant available and a polarizing species among aquarium keepers. Some love duckweed for its nutrient-export capacity (it strips nitrate and phosphate from the water aggressively), its usefulness as live food for herbivorous fish and shrimp, and its role as shade for sensitive species. Others despise it because once introduced, it's nearly impossible to eradicate; it fragments into tiny pieces that persist through water changes, net sweeps, and even complete teardowns. A single overlooked frond restarts the population. In aquaponics, duckweed is a valuable supplemental feed: high in protein (25-45% dry weight), fast-growing, and harvestable continuously. Many tilapia, goldfish, and carp operations use duckweed as a portion of the fish diet. Requirements are minimal: any light above dim, any temperature from 5–35°C, any water chemistry. Growth is fastest in warm (25–30°C), nutrient-rich, still water with strong light. Surface agitation from filters slows duckweed growth and pushes it into corners; still water lets it cover the surface evenly. The main maintenance task is harvesting: skim excess duckweed with a net 2-3 times per week to prevent complete surface coverage that blocks light to submerged plants.