sealPurdue News

November 25, 2002

November last call for winterizing garden ponds

WEST LAFAYETTE, Ind. – Most people don't associate November with gardening, but for water gardens this is the last month to prepare those sites for winter.

Carole Lembi, a professor of botany at Purdue University, said there are several steps to getting a water garden ready for winter, especially if fish or plants are involved. Lembi said that while large natural ponds don't require any special preparations, smaller ornamental pools, like those found in many gardens, have to be readied for winter.

"Many people do not realize how much maintenance and management water gardens need," Lembi said.

Cleaning leaves and other debris from the site is one of the first things a water garden owner should do. It's a chore that can last months – especially in Indiana and other parts of the Midwest – but Lembi said it's a vital step to keep pond water healthy. Decaying leaves give off gases that dissolve in water and can harm the fish. After cleaning, it's a good idea to cover the pond with a net or screen to keep additional leaves out.

Emergent plants, such as reeds, rushes and cattails, should be cut back. As they decompose, they can add litter and organic matter to the edge of the pond, Lembi said. Water lilies should be pruned to just about the crown and placed in the deepest portion of the pond. Other tender plants also should be positioned in the deepest water. The goal is for the tender plants to remain ice-free, Lembi said.

She said tropical plants should be moved indoors. Those plants will overwinter in the house with a large container of water and strong light. Floating plants, such as water hyacinth and water lettuce, should be removed and discarded.

Most ponds do not require a water change. Change the water if it's extremely discolored or dirty. Even then, only exchange about two-thirds of the water and make sure to complete the change before water temperature drops below 50 degrees Fahrenheit so fish are not disturbed.

Water temperature is the most reliable gauge for fish care, according to Paul Brown, a professor of forestry and natural resources. Decrease feedings when the water temperature stays below 50 degrees Fahrenheit. At that point fish metabolism slows, and they don't require as much food.

In Indiana fish can overwinter in ponds that are more than 2.5 feet deep – shallower ponds can freeze solid, sometimes killing the fish. In some areas the ponds must be deeper. If the deepest portion of the pond is below the local freezing line, the water should be safe for fish, Brown said.

"Ice formation is not necessarily a bad thing, it's ice formation with snow on top that causes problems," he said.

It's important to keep the pond's surface clear so that photosynthesis – the process by which green plants use sunlight to convert carbon dioxide dissolved in water to sugars and oxygen – can occur over the winter. Snow cover keeps light from entering the water. If plants are unable to perform photosynthesis, they won't add oxygen back into the water and fish can suffocate, Brown said.

Lembi said a pond heater that's approved for plastic ponds is one option for small ornamental pools. Stock tank or birdbath heaters are other, sometimes less expensive, options.

Following pond care guidelines will help keep fish and plants alive over the winter, Lembi said, but it doesn't mean every plant or fish will make it to next spring. If fish die one year, then allow others to overwinter inside the following year. The same can be said for especially important or expensive plants.

Writer: Kay Hostetler, (765) 494-6682,

Sources: Carole Lembi, (765) 494-7887,

Paul Brown, (765) 494-4968,

Ag Communications: (765) 494-2722; Beth Forbes,;

Purdue News Service: (765) 494-2096;

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