Soil & potting mix
Best soil for Greater Duckweed (Spirodela polyrhiza)
Also called Greater Duckweed, Common Duckmeat, Giant Duckweed.
More about greater duckweed
About Greater Duckweed
Spirodela polyrhiza · also called Greater Duckweed, Common Duckmeat · flowering
Greater Duckweed is the largest of the common duckweeds, with flat, rounded fronds 3–10 mm across bearing multiple rootlets on the underside. Native to every continent except Antarctica, it rapidly covers still water surfaces, providing shade to limit algae and shelter for invertebrates. An important waterfowl food and natural water-quality indicator.
Preferred mix: Free-floating — no substrate
Why greater duckweed needs this mix
Greater Duckweed grows on air — it has almost no functional root system for feeding, so it is never planted in soil at all.
- Greater Duckweed absorbs moisture and nutrients through specialised scales on its leaves, so a pot of soil does nothing useful and only traps damaging moisture against its base.
- Its few roots exist mainly to anchor it to bark or rock — they are not feeding roots and rot quickly if buried.
- Free air movement is essential: it must dry within a few hours of every watering or the centre rots.
For the full picture on what makes up a good mix, see our guide to the main types of soil and potting media — it explains why each ingredient above behaves the way it does.
What goes wrong with the wrong mix
The wrong soil is one of the most common reasons greater duckweed struggles, and the damage often shows up weeks later as a watering problem. For this species specifically:
- Potting greater duckweed in soil or packing moss around its base is the classic killer — the crown stays wet and goes black and mushy from the inside.
- Sitting it in a closed terrarium or sealed glass globe with no airflow has the same effect more slowly.
- Glued-onto-a-shell ornaments trap water under the base and rot it; if you have one, prise it off.
Planting greater duckweed in any kind of soil or substrate, or displaying it somewhere it cannot dry out within hours of watering.
pH — does it matter for greater duckweed?
pH is irrelevant for greater duckweed — there is no soil. What matters is water quality: use rain or filtered water, as it is sensitive to tap-water minerals.
If you want to check or adjust it, the soil pH guide walks through testing and the safe ways to nudge a mix more acidic or more alkaline.
DIY mix vs a bagged one
There is no mix to buy or make for greater duckweed. "DIY vs bagged" does not apply — instead invest in a mount, wire or fishing line and a bright, airy spot.
Drainage and the pot
Drainage means airflow here: after soaking or misting, turn greater duckweed upside down to shed water from its centre and let it dry fully before returning it to its display.
There is nothing to repot. Simply re-mount greater duckweed if it outgrows its slab, and never wrap its base in moss that stays wet. When the time comes, our repotting guide for greater duckweed covers the timing and technique step by step.
Greater Duckweed soil — frequently asked questions
What is the best soil mix for greater duckweed?
No soil — display bare, in an open vessel, or wired to a mount or slab. Greater Duckweed absorbs moisture and nutrients through specialised scales on its leaves, so a pot of soil does nothing useful and only traps damaging moisture against its base.
Can I use normal potting soil for greater duckweed?
Potting greater duckweed in soil or packing moss around its base is the classic killer — the crown stays wet and goes black and mushy from the inside. There is no mix to buy or make for greater duckweed. "DIY vs bagged" does not apply — instead invest in a mount, wire or fishing line and a bright, airy spot.
Does greater duckweed need a special pH?
pH is irrelevant for greater duckweed — there is no soil. What matters is water quality: use rain or filtered water, as it is sensitive to tap-water minerals.
Should I buy a bagged mix or make my own for greater duckweed?
There is no mix to buy or make for greater duckweed. "DIY vs bagged" does not apply — instead invest in a mount, wire or fishing line and a bright, airy spot.
How often should I refresh the soil for greater duckweed?
There is nothing to repot. Simply re-mount greater duckweed if it outgrows its slab, and never wrap its base in moss that stays wet. Drainage means airflow here: after soaking or misting, turn greater duckweed upside down to shed water from its centre and let it dry fully before returning it to its display.
Keep reading
- Greater Duckweed care — the full brief (light, water, humidity, problems, pet safety)
- How often to water greater duckweed — the schedule the mix feeds into
- Repotting greater duckweed — when and how to refresh the mix
- Soil pH guide — test it and adjust it safely
- Overwatered plant — signs and recovery
- Root rot — how the wrong soil starts it, and how to save the plant
- Why is my plant wilting? Wet vs dry diagnosis
- Best soil for stanhopea tigrina
- Best soil for rodriguezia secunda
- Best soil for aerangis luteoalba
- All 8452 soil and potting-mix guides in the Growli library