About the species

Spirodela polyrrhiza, or greater duckweed, is a floating plant with round green fronds that lie free on the water surface. Each frond is only a few millimetres across and carries a small bunch of roots underneath, and the plants divide at a furious rate. The result is a pond-like, natural impression and pleasant shade below the surface.

Facts

• Latin name: Spirodela polyrrhiza
• Plant type: Floating plant
• Origin: North America
• Height: 3–5 cm
• Growth rate: Fast
• Position: Water surface

Light requirement

Low light requirement. It manages with the lighting that comes with most aquariums and is happy in partial shade behind or beneath taller plants. Strong lighting does not harm it, but raises the risk of algae on the leaves because the plant cannot use all the available light.

CO₂ & nutrition

Manages entirely without added CO₂, which makes it as suitable for a simple aquarium as for an aquascape. Liquid carbon or injected CO₂ speeds up growth but is never a requirement. Dose an all-round fertiliser with iron and micronutrients every week.

Planting

A floating plant is not planted — simply lay it on the water surface. It wants a calm surface, so aim the filter outlet downwards or fence off part of the surface with airline tubing or a floating frame. Leaves that get wet from above rot easily.

Rinse all the gel off in lukewarm water before planting, otherwise it can cause bacterial cloudiness. The cup holds many small plants — divide them up and plant them in several portions.

Care & propagation

Keep the quantity in check every week — floating plants multiply quickly and will otherwise shade out everything below them. That is also their great strength: they absorb surplus nutrients and give the pleasantly diffused light that shrimp and shy fish appreciate.

Position in the aquarium

It belongs on the water surface and needs no space in the substrate. Let it cover part of the surface — the shade beneath is exactly what shrimp, shy fish and shade-tolerant plants want.

Difficulty level

🟢 Easy — grows in most aquariums without CO₂ and under ordinary lighting.

Delivery format

Delivered as 1-2-Grow! — a laboratory-grown cup holding many small plants in nutrient gel. Because the plant is cultivated in vitro it is completely free of snails, algae, planaria and pesticides, which makes it the safest choice for a shrimp aquarium.

Recommendation

An effective way to mop up surplus nutrients and keep algae at bay, and at the same time reassuring cover for shy fish and shrimp. Expect to net out a share every week — duckweed is notoriously hard to get rid of completely.