Overwintering your aquatic plants: hardy, semi-hardy, and tropical

Every autumn, the same question comes up at the counter: “What should I do with my pond plants before winter?” The answer depends entirely on the plant. Native and hardy aquatic plants only need cleaning and sometimes need to be lowered a little deeper; half-hardy plants must be protected from frost; tropical plants must be brought indoors or treated as annuals. The problem is that you cannot always tell which category a plant bought in full bloom in June belongs to. Here is how to sort them, plant by plant, and what to do in practical terms.

Why some plants do not survive

An aquatic plant rarely dies “from the cold” in the strict sense. It dies because its vital organs, rhizome, tuber, or buds, have frozen, or because they have rotted in cold, oxygen-poor water. Three factors come into play:

• The plant’s origin. Native species from Western Europe are adapted to our winters. Tropical or subtropical species do not enter true dormancy and cannot tolerate water close to 0 °C for weeks.
• The position in the pond. Still water freezes from the surface. The deeper you go, the more stable the water remains, at around 4 °C at the bottom of a sufficiently deep pond. A rhizome placed on a shelf 10 cm deep may become trapped in ice; the same rhizome at 60 cm does not freeze.
• The plant’s health at the start of winter. A plant covered in decomposing leaves, in a basket filled with sludge, spends the winter in a low-oxygen environment. Autumn cleaning is therefore just as important as protection from the cold.

Hardy plants: clean and lower

For hardy marginal and marsh plants, autumn maintenance consists of a few tasks, to be carried out between mid-October and the end of November, depending on the year:

1. Remove dead leaves that have fallen into the water with a fine-mesh net, before they sink.
2. Cut back faded foliage of marsh plants a few centimeters above the water. Do not cut hollow-stemmed plants (irises, rushes, cattails, pickerelweed) below the surface: water could seep into the rhizome.
3. Leave a few dry stems on the banks: they shelter insects and allow gas exchange when the surface freezes.
4. Check the baskets: a cracked or overturned basket should be put back in place now, not in spring.
5. Lower by one level the most sensitive marsh plants placed on bricks, so that their crown is beneath a few extra centimeters of water.

Put the cut leaves in the compost. They must not remain in the pond, where their decomposition consumes oxygen and releases nutrients that will feed algae in spring.

Water lilies and lotus

Hardy water lilies. The vast majority of water lilies sold at garden centers are hardy. They survive winter without difficulty if their rhizome remains below the frost line. In autumn, remove yellowed leaves at the rhizome, and lower baskets placed on a ledge toward the deepest part of the pond, ideally 60 cm or more. Dwarf varieties planted in tubs or barrels are more exposed: their volume of water sometimes freezes all the way to the bottom. In that case, bring them into a frost-free garage, with a few centimeters of water above the rhizome.

Tropical water lilies. Recognizable by their flowers held above the water and their often toothed leaves, they cannot tolerate winter outdoors. The classic method is to remove the pot in autumn, let the plant form small tubers, then store these tubers in a jar of water or in damp sand, somewhere cool but frost-free, before restarting their growth in spring in warm water. This is a technique for experienced hobbyists; many gardeners prefer to buy a new plant each year.

Lotus. The rhizome tolerates cold water but must never freeze. Let the foliage turn yellow, cut it above the water, then lower the basket to the bottom of a deep pond or, for a lotus in a container, bring the container indoors to a frost-free place while keeping the substrate soaked.

Tropical floating plants

For years, water hyacinth and water lettuce were the star floating plants of summer ponds. Water hyacinth (Eichhornia crassipes) is on the list of invasive alien species of concern to the European Union, and water lettuce (Pistia stratiotes) joined it more recently: their sale, cultivation, and exchange are prohibited. If you still have older plants, do not try to overwinter or propagate them: remove them and dispose of them with green waste, far from any ditch or watercourse.

For floating plants that are still authorized, the approach is simple:

Overwintering tropical floating plants indoors requires light, often 10 to 12 hours a day, and water around 18 to 22 °C. Without supplemental lighting, they become spindly. Many enthusiasts keep only a few plants in an aquarium to restart production in spring.

Winter-blooming

Native oxygenating plants, such as coontail (Ceratophyllum demersum), whorled water-milfoil, and water crowfoot, slow down considerably in winter but remain in place. Some, like coontail, form winter buds that rest on the bottom.

• In autumn, thin out overly dense growth with a net or tongs to limit the amount of material that will decompose during winter. Never remove everything.
• In winter, leave them alone. They continue to produce a little oxygen in bright weather, even beneath a thin layer of ice.
• Beware of regulated species: Nuttall's waterweed, lagarosiphon, cabomba, and Brazilian watermilfoil are on the European list of invasive species and must no longer be planted.

An oxygenating plant that turns yellow and deteriorates in late autumn is not necessarily dead: many regrow from the bottom as soon as the water rises above about ten degrees.

Bring plants indoors: bucket, cellar, aquarium

Bringing an aquatic plant indoors means providing conditions suited to its hardiness. Three solutions cover most cases:

Whatever the method, two rules: never let the substrate of a dormant aquatic plant dry out, and avoid heat for plants that need to remain dormant. A lotus rhizome placed in a heated utility room starts growing too early, becomes exhausted, and produces weak shoots.

Common case: a papyrus bought in June, splendid all summer beside the pond, left outside in October. On the first chilly nights, it turns yellow, then collapses after the first frost. Brought indoors in time to a bright room, with the saucer kept full of water, it would have spent the winter like a houseplant and been brought back outside in May.

Spring growth resumes

Spring is the time to repair minor losses and get the season going again. Wait until the pond water remains above 10 to 12°C before carrying out substantial maintenance.

1. Clean the dry stems left in place and remove dead leaves that have accumulated on the bottom.
2. Raise water lilies and marsh plants gradually to their summer depth.
3. Divide clumps that have become too large (iris, rushes, marsh marigold) and repot them in fresh substrate.
4. Bring out plants overwintered indoors after the last frosts, acclimatizing them in the shade for a few days.
5. Fertilize water lilies and lotuses moderately with tablets pushed into the substrate once growth has resumed properly.

A plant that does not start growing again by the end of May while its neighbors are growing vigorously is probably lost: a soft, foul-smelling rhizome will not recover.

Summary table

For the rest of your pond's winter maintenance, our guide Preparing your pond for winter completes this list with information on fish and equipment. To restart your pond, see how to maintain your garden pond after winter, and for growing water lilies the rest of the year, how to grow a water lily.

Also read

For pond maintenance during the cold season: The right steps for your lake or pond in winter.

READ THE ARTICLE

Frequently asked questions

— Should aquatic plants be cut back in autumn?

Cut faded foliage above the surface, never underwater on hollow stems such as irises or rushes. Keep a few dry stems for wildlife and gas exchange.

— Do water lilies survive the winter in the pond?

Hardy water lilies can, provided their rhizome is below the freezing zone, ideally around 60 cm or deeper. Tropical varieties must be brought indoors.

— Can water hyacinth be overwintered?

No. Water hyacinth is an invasive alien species regulated in the European Union: its cultivation and propagation are prohibited. It must be disposed of with green waste.

— Where should a semi-hardy aquatic plant be stored over winter?

In a frost-free garage or cellar, kept cool, with a consistently moist substrate or a few centimeters of water. Warmth would make it start growing again too early.

In summary

• Classify your plants: hardy, semi-hardy or tropical.
• Hardy plants: clean them, cut the foliage above the water, and lower water lilies below the frost line.
• Semi-hardy plants: at the bottom of the pond or kept cool and frost-free, with a consistently moist substrate.
• Tropical plants: indoors with light and warmth, or grown as annuals.
• Water hyacinth and water lettuce: prohibited, to be removed and not overwintered.

Last updated: October 3, 2026.