Sodate
On this page
Duckweed is legal in most places, costs almost nothing (fish shops often give it away), and is genuinely useful: it strips nitrates, shades algae out, and feeds goldfish, koi, and poultry. The catch is control, not care — it can double in under a week and will carpet any still, nutrient-rich surface. Skim regularly, keep it out of filters, and never dump it into natural water: escaped mats can smother small ponds and ditches.
Key facts
- Among the fastest-multiplying plants known — fronds bud clones and populations can double in 2-7 days in warm, rich water.
- Legal in most jurisdictions (it is native across much of the world), but it still carries a pond-takeover risk: a full carpet blocks light and gas exchange and can deoxygenate small ponds.
- It grows with zero equipment: no substrate, no CO2, no dosing in most setups — it lives entirely off dissolved nutrients, which is why it is used in wastewater treatment.
- Effectively free: a golf-ball portion from a fish shop (often given away) seeds an entire pond in weeks.
Care requirements#
| Plant type | Free-floating aquatic; tiny 2-5mm fronds with a single hanging rootlet |
| Growing medium | None — floats on the surface and absorbs nutrients directly from the water |
| Water temperature | 6-33°C tolerated; fastest growth 20-28°C (68-82°F) |
| Light | Moderate to bright light over the tank or pond; grows in almost anything above dim |
| Nutrients | Feeds on nitrates/phosphates in the water; needs no dosing in any tank with fish |
| Water hardness | Very tolerant, soft to hard; pH ~5.5-8.5 |
| Flow preference | Still surface essential — current and surface agitation push it under and shred it |
| Filter protection | Keep intakes screened with a sponge prefilter; duckweed clogs filters fast |
| Containment | Corral with airline tubing or a floating ring if you want only partial coverage |
| Harvesting | Skim with a net weekly (more in summer); feed to fish/poultry or compost |
| Winter (ponds) | Hardy — forms sinking resting buds (turions) that overwinter on the bottom and refloat in spring |
| Toxicity | Non-toxic; eaten by fish, ducks, and poultry, and researched as a protein crop |
Growth & propagation#
| Mature size | Individual fronds 2-5mm; colonies of 2-4 fronds |
| Growth rate | Explosive — doubling in 2-7 days under good conditions |
| Propagation methods | Vegetative budding (cloning); flowers exist but are vanishingly rare and unnecessary |
| Propagation difficulty | Unavoidable — a few fronds become a carpet |
| Coverage | Can fully carpet a still pond in a few weeks in summer |
| Lifespan | Individual fronds live weeks; the clonal colony is effectively immortal |
Common problems & troubleshooting#
| Symptom | Likely cause | Fix |
|---|---|---|
| Complete green carpet, gasping fish | Unchecked coverage blocking light and oxygen exchange | Skim hard down to ~30-50% coverage and keep a weekly skimming routine |
| Duckweed disappearing from the tank | Surface agitation, strong flow, or hungry fish (goldfish and koi devour it) | Calm the surface with a spray-bar adjustment or corral a protected patch; accept it as live food |
| Fronds turning pale or white | Nutrient depletion — it has stripped the water column | Thin the population, or in plant-only tubs add a weak liquid fertilizer |
| Filter flow dropping | Fronds sucked into the intake | Fit a sponge prefilter or intake guard; skim more often |
| It's in every tank I own | Fronds hitchhike on nets, hands, and plants | Dedicate a net, rinse equipment, and quarantine new plants — once in, eradication is genuinely hard |
Skim on schedule, not on panic
Sodate reminds you to skim the duckweed weekly — the difference between free fish food and a green ceiling.
Seasonal care#
Buying checklist#
- Check local rules first — legal most places, but a few jurisdictions regulate aquatic plant release; never dump it in natural water
- You barely need to buy it: fish shops often give portions away or sell for $1-4
- Ask for a clean, snail-free culture, or quarantine and rinse it before adding to your tank
- Only add it if you accept permanent residency — full removal later is very difficult
Pricing by region#
| Region | Price range | Typical unit | Basis |
|---|---|---|---|
| US | $0 – $5 | portion/cup | Fish-shop giveaway or online portion with shipping |
| UK | $0 – $5 | portion | Aquarium shops and pond forums |
| India | $0 – $1 | portion | Aquarium shops; abundant in local ponds |
| Australia | $2 – $7 | portion | Aquarium retail (native Lemna species sold domestically) |
| Canada | $0 – $5 | portion | Fish-shop giveaway or online portion |
USD figures are approximate conversions for comparison; switch the dropdown to see each region's actual local-currency listing price.
Often confused with#
Where it's actually grown#
Almost never commercially farmed for the hobby — shop stock is skimmed from holding tanks and grower ponds, and most hobbyists get theirs free from other fishkeepers; dedicated duckweed farms exist only for animal feed, wastewater treatment, and protein research.
Import & biosecurity restrictions#
| Region | Note |
|---|---|
| US | Native and unregulated in most states; a few states regulate aquatic plant sale/transport generally — never release cultures into natural water regardless. |
| UK | Native and legal; 'Be Plant Wise' guidance still applies — compost surplus, never tip pond water into waterways. |
| India | Native/naturalised and unrestricted; widely present in ponds and tanks already. |
| Australia | Live plant imports prohibited under biosecurity law, but native Lemna species are sold domestically by aquarium retailers. |
| Canada | Native and legal; keep cultures out of storm drains and natural ponds all the same. |
Similar plants
Did you know?
Frequently asked questions
Is duckweed legal to keep?
Yes in most places — Lemna minor is native across much of the world — but never release it into natural water, and check local aquatic-plant rules if you're unsure.
Will duckweed take over my pond?
It can carpet a still, nutrient-rich pond in a few weeks, which blocks light and oxygen; weekly skimming to keep at least half the surface open prevents this.
Is duckweed good for fish?
Yes — it strips nitrates, shades out algae, gives fry cover, and goldfish, koi, and many other fish eat it readily as a free live food.
How do I get rid of duckweed?
Persistent manual skimming plus hungry fish (goldfish/koi) works in tanks and small ponds, but total eradication is hard because a single missed frond restarts the colony.
How much does duckweed cost?
Almost nothing — fish shops often give it away, and online portions run a few dollars, mostly for the shipping.