Duckweed is among the smallest flowering plants on Earth, yet it almost never needs its flowers to spread. Nearly all of its life goes into copying itself, with each tiny plant producing ready-made offspring that drift off and do the same. When autumn arrives, many duckweeds change course and put their energy into a hardier winter form instead of ordinary plants. The green carpet that seems to vanish from a pond in winter usually hasn’t died out, and its comeback is built into the cycle.
How Duckweed Multiplies by Budding
A duckweed plant is a frond, a flat green body that does the work of stem and leaf together. In common duckweed a mature frond is about 3 to 4 mm wide.1PubMed Central. Characterization of Frond and Flower Development and Identification of FT and FD Genes From Duckweed Lemna aequinoctialis Nd Near its narrow end sit two small pockets, called budding pouches, where new fronds form.2PubMed Central. Characterization of Frond and Flower Development and Identification of FT and FD Genes From Duckweed Lemna aequinoctialis Nd A patch of constantly dividing young cells at the base of each pouch keeps the new fronds coming.3PubMed Central. Frond architecture of the rootless duckweed Wolffia globosa The tiniest duckweeds, the rootless Wolffia, manage with a single pouch.4Flora: Morphology, Distribution, Functional Ecology of Plants. The duckweed Wolffia microscopica: A unique aquatic monocot
Daughter fronds grow alternately, first from one pouch and then the other.5PubMed Central. Characterization of Frond and Flower Development and Identification of FT and FD Genes From Duckweed Lemna aequinoctialis Nd When a daughter is mature, it snaps off and leaves a small scar on the mother, and the next daughter starts growing right beside that scar.6PubMed Central. Characterization of Frond and Flower Development and Identification of FT and FD Genes From Duckweed Lemna aequinoctialis Nd One mother therefore turns out a steady series of daughters, and each begins budding while still young. Mothers do age. Older fronds survive less well, bud less often and produce weaker daughters than young ones.7Functional Ecology. Senescence in duckweed: age‐related declines in survival, reproduction and offspring quality
Look closely at a clump and you will often see fronds stuck together in twos, threes or fours, because daughters stay attached for a while. The smaller frond in a group is the younger daughter, still growing in its pouch. Common duckweed has one thin root hanging under each frond, while Wolffia looks like green grains with none.
Because each daughter is a genetic copy of its mother, no partner or pollen is needed. One frond carried in on a net or a new plant can become a whole mat.
How Fast Duckweed Grows and What Speeds It Up
Under ideal indoor conditions, duckweed has doubled its amount in as little as 1.24 days.8Journal of Cleaner Production. Duckweed bioreactors: Challenges and opportunities for large-scale indoor cultivation of Lemnaceae Outdoors, weather, shade and nutrients usually hold it below that speed.
Temperature sets the season. Most duckweeds grow best between about 20 and 30 °C (68 to 86 °F).9PubMed Central. Survival Strategies of Duckweeds, the World’s Smallest Angiosperms Growth crawls to a very slow rate somewhere between under 8 °C and 16 to 20 °C, depending on the type, and long-lasting heat above roughly 30 to 34 °C slows it again.10PubMed Central. Survival Strategies of Duckweeds, the World’s Smallest Angiosperms In temperate ponds the big surge comes in the warm months, and summer and autumn were the peak duckweed seasons in one wetland.11PubMed. Aquatic phosphorus behaviour within a UK Ramsar wetland: Impacts of seasonality and hydrology on algal growth and implications for management
Light matters too. Raising the light raised growth rates by around two thirds or more.12PubMed Central. Influence of Light Intensity and Spectrum on Duckweed Growth and Proteins in a Small-Scale, Re-Circulating Indoor Vertical Farm The benefit levels off, though, and beyond a point extra light adds little.13PubMed. Integrated effects of light intensity, spectral composition and photoperiod fragmentation on growth and nutrient removal of three duckweed species The colour of light matters much less than its amount,14PubMed Central. Influence of Light Intensity and Spectrum on Duckweed Growth and Proteins in a Small-Scale, Re-Circulating Indoor Vertical Farm and steady daylight works better than light broken into short on-off bursts, even with the same total.15PubMed. Integrated effects of light intensity, spectral composition and photoperiod fragmentation on growth and nutrient removal of three duckweed species
Duckweed thrives in water rich in nutrients like nitrogen and phosphorus. It can grow on wastewater, though more slowly in polluted landfill runoff than in clean nutrient solution.16PubMed Central. Growth and nutrient removal efficiency of duckweed (lemna minor) from synthetic and dumpsite leachate under artificial and natural conditions Salty water reduces its growth and survival.17PubMed. Resilience to multiple stressors in an aquatic plant and its microbiome
A pond can seem to go green overnight because doubling hides itself. Growth looks slow for weeks, then sudden as the numbers compound, and going from half covered to fully covered takes only one doubling. If a quarter of the surface is covered, full cover could follow after about two more doublings if conditions stay favorable.
A sunny, sheltered, still pond suits duckweed more than a shaded or moving one. Runoff from lawns, livestock or fish waste feeds it, while moving water and wind push fronds to the edges and slow the spread.
If you are growing it on purpose, keep the water warm and well lit, as aquarists and feed growers do. Thinning the mat regularly keeps fronds young and fast-budding.
When Duckweed Flowers and Makes Seeds
A duckweed flower is reduced to a single female part and one or two pollen-bearing stamens tucked into the frond.18Trends in Genetics. Duckweeds as a model for minimal floral development These flowers evolved by shrinking from the larger flower spikes of relatives in the arum family, like peace lilies.19Trends in Genetics. Duckweeds as a model for minimal floral development
Flowering is unreliable. It often depends on day length, and some duckweed flowers only under long days.20PubMed. Carbon monoxide promotes flowering in Lemna gibba via a nitric oxide-dependent oxidative stress pathway Stress-related chemical signals can trigger flowering in lab conditions.21PubMed. Transcriptional analysis reveals potential genes and regulatory networks involved in salicylic acid-induced flowering in duckweed (Lemna gibba) Even when flowers form, some strains have stamens that never open to release pollen.22PubMed Central. Flower induction, microscope-aided cross-pollination, and seed production in the duckweed Lemna gibba with discovery of a male-sterile clone Many mats in ponds never set seed at all. A plant that spreads by cloning still keeps flowers because seeds mix genes, giving offspring new combinations, and can survive conditions that kill fronds, like drying. A mat that never flowers can still be perfectly healthy and keep growing.
When seeds do form, they can wait in pond mud.23Acta Botanica Brasilica. Influence of storage and temperature on the germination of a macrophyte seed bank from a temporary pond in the Brazilian semiarid Duckweed seeds from a seasonal pond sprouted across every temperature tested,24Acta Botanica Brasilica. Influence of storage and temperature on the germination of a macrophyte seed bank from a temporary pond in the Brazilian semiarid which suggests seeds may help duckweed return after a pond dries out.
If you want to spot one, look for tiny pale bumps at a frond’s edge near the pouch. A pinhead stamen may poke out with yellowish pollen.
How Duckweed Survives Winter as Turions
A turion, or winter bud, is a small, dark, dense bud made in place of a normal daughter frond. It is packed with stored starch, which made up over 60% of its dry weight in one test.25PubMed Central. Analysis of ADP-glucose pyrophosphorylase expression during turion formation induced by abscisic acid in Spirodela polyrhiza (greater duckweed) Inside, the cells have smaller water spaces and less air than ordinary fronds.26PubMed Central. Analysis of ADP-glucose pyrophosphorylase expression during turion formation induced by abscisic acid in Spirodela polyrhiza (greater duckweed) Heavy and low on air, turions sink to the pond bottom.
In greater duckweed, running low on nutrients, especially phosphate, is the main trigger.27PubMed Central. The Developmental Cycle of Spirodela polyrhiza Turions: A Model for Turion-Based Duckweed Overwintering? Cooling autumn temperatures act as a backup, causing winter buds even when nutrients remain.28PubMed Central. The Developmental Cycle of Spirodela polyrhiza Turions: A Model for Turion-Based Duckweed Overwintering? A plant stress hormone can flip the same switch.29PubMed Central. The Developmental Cycle of Spirodela polyrhiza Turions: A Model for Turion-Based Duckweed Overwintering? The same budding pockets that made ordinary daughters start making winter buds instead.30PubMed Central. The Developmental Cycle of Spirodela polyrhiza Turions: A Model for Turion-Based Duckweed Overwintering? Inside, forming a winter bud turns on genes for stress tolerance, for storing starch and fats, and for dormancy.31bioRxiv. Genomics of turions from the Greater Duckweed reveal its pathways for dormancy and reemergence strategy That lets the buds rest through cold water that would stop ordinary fronds.32bioRxiv. Genomics of turions from the Greater Duckweed reveal its pathways for dormancy and reemergence strategy
Not every duckweed does this. Greater duckweed is the classic winter bud maker. Many common duckweeds instead overwinter as slow-growing or sunken fronds, and in mild climates duckweed may keep growing slowly all winter. A net skimming the surface in late autumn can miss much of the colony, because the buds are already below it.
How Duckweed Returns in Spring and Reaches New Ponds
As water warms in spring, winter buds use their stored starch and fats to start growing.33bioRxiv. Genomics of turions from the Greater Duckweed reveal its pathways for dormancy and reemergence strategy They lighten and float to the surface, where new fronds emerge. Once temperatures climb toward that 20 to 30 °C range, budding speeds up again. Buds in a cold, shaded pond wake later than those in a sunny shallow one.
Water birds regularly carry small water plants and seeds stuck to feathers and feet between nearby ponds.34Freshwater Biology. Up, up and away: bird‐mediated ectozoochorous dispersal between aquatic environments Duckweed can therefore appear in a new pond with no one planting it, and a single carried frond is enough to start a mat by budding.
It moves in other ways too. Fronds cling to boots, nets, boats and pets. New aquarium or pond plants often carry stowaways, and flooding can wash mats between connected ponds.
Using the Life Cycle to Control or Harvest Duckweed
When ditches and ponds become dominated by duckweed or algae, the water underneath can run out of oxygen.35PubMed. Aquatic phosphorus behaviour within a UK Ramsar wetland: Impacts of seasonality and hydrology on algal growth and implications for management Fish and submerged plants may struggle under a thick mat.
Control is easiest early in the growing season, when a few skimmings can remove most of what is there before it doubles again. A mat thick enough to hide the water is a warning sign, so check that fish aren’t gasping near the surface and that the water doesn’t smell foul. If oxygen is clearly low under heavy cover, removing a large share of the mat helps more than waiting, though removing it all at once can disturb the pond.
Skimming before autumn removes plants before they can make winter buds, though any buds already on the bottom can still regrow in spring. Harvesting also pulls phosphorus out of the water, an estimated 39 kg per harvest period in one large wetland.36PubMed. Aquatic phosphorus behaviour within a UK Ramsar wetland: Impacts of seasonality and hydrology on algal growth and implications for management Regular removal therefore cuts the nutrient supply that feeds next year’s growth.
A practical routine starts with skimming with a fine net every week or two in summer, before the mat doubles again. Compost what you remove well away from the pond. Reduce fertilizer runoff and overfeeding of fish, and add surface movement with a fountain or pump.
Duckweed can contain up to 45% protein, making it useful as animal feed.37Journal of Cleaner Production. Duckweed bioreactors: Challenges and opportunities for large-scale indoor cultivation of Lemnaceae Stacked indoor growing systems produce it year-round regardless of weather,38Aquacultural Engineering. Where engineering meets biology: The Computational Fluid Dynamic analysis of a stacked duckweed bioreactor and it is used to clean farm and food wastewater.39PubMed. On the rise: Development of a multi-tiered, indoor duckweed cultivation system
For chickens, ducks or fish, shallow tubs in sun with some nutrient give steady harvests. Harvest a portion often to keep fronds young. Avoid growing it in polluted water if you are feeding animals.