Floating pond plant
Common duckweed
Lemna minor
A tiny free‑floating aquatic plant that can provide useful wildlife cover at low density but multiplies rapidly to form mats and become a nuisance in ponds.
PLANT PROFILE
About Common duckweed
Common duckweed (Lemna minor) is a minute, free‑floating perennial that occurs on the surface of still or slow‑moving waters such as garden ponds and ditches. Individual plants are single leaf‑like fronds usually not exceeding about 5 mm across, each typically bearing one or more slender submerged roots of around 15 mm. It multiplies vegetatively and can double rapidly in warm, nutrient‑rich conditions, allowing it to form dense floating carpets that may completely cover a pond surface.
For pond owners in the UK, Lemna minor can be an asset at low densities: RHS describes a small carpet of duckweed as a good addition to wildlife ponds because it provides shelter and a protein‑rich food source for waterfowl, offers cover for amphibians, and supports aquatic invertebrates. However, it can also be a nuisance in ornamental or stocked ponds where rapid multiplication shades out other plants and can reduce oxygen levels in the water.
Management and prevention are therefore important. Quarantine new or shared pond plants (keep them temporarily in a separate container) and inspect for duckweed on purchased material. Control techniques shown to be effective include regular manual removal with a net or rake (especially in summer), using booms or sweeps on larger waters, creating shade (for example with tall marginal plants on the sunny bank), installing surface disturbance (fountains), and introducing grazers in larger ponds. RHS notes a non‑chemical bacterial product (marketed as a nutrient‑reducing option) and also states that there are no chemical weedkillers approved for home gardeners to remove duckweed. Freshwater Habitats Trust emphasises tackling the underlying cause by reducing nutrient inputs to the pond. Removed material should be disposed of responsibly to avoid spreading plant fragments.
Lemna minor is treated as a common native duckweed in UK pond guidance and surveys, but because it can rapidly dominate a pond surface, regular monitoring and prompt, non‑chemical intervention are recommended for garden pond keepers.
POND SUITABILITY