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Winterizing Water Plants

Landscaping Information: How to Winterize Your Water Plants

Getting Started:Pond owners should begin preparing for winter when the water temperature drops below 55 degrees. The most important step in overwintering any pond is thorough cleaning. This is very important. Dead leaves and decaying organic matter can become a haven for certain parasites and disease-causing bacteria that could flair up as water temps begin to rise in the spring. Once the pond is clean, it should be covered with netting to keep out any fallen leaves and debris throughout the winter months.

It’s Time to Winterize…
As the temps begin to drop and days grow shorter, it’s time to get your ponds, plants and fish ready for the long winter months. The over-wintering of each pond will vary somewhat based on climate zones and the species kept. The following information will make it a lot easier and successful for pond overwintering.

Prepping the Plants:

There are several commonly made mistakes pond owners make when they prepare their plants for winter. First, they cut their plants back too soon. Cutting aquatic plants back while they’re still in the growing phase can hinder their ability to store up its resources for winter. A second common mistake is cutting back marginal plants that have hollow stems. If the stem is cutback in the fall, it will fill with water and rot the plant’s crown. Cut these plants back only in the spring. Third, don’t try to overwinter plants in a pond that isn’t deep enough. To properly overwinter most hardy water plants, they must be at a water depth of 18” or greater or planted in planting pockets to prevent freezing the crown and killing the plant. Greater details are given on the back page to help you overwinter your specific water plants.

Ready the Fish:

To safely overwinter fish, you should focus on three factors: Pond depth, seasonal feeding requirements and maintaining an air hole.

  1. If a pond is deep enough, fish can survive in a pocket of water near the bottom of the pond. Goldfish species generally need at least one area that is at least 2 feet deep. Koi generally have greater needs and require an area approximately 3 feet deep to safely overwinter.
  2. When the water temp drops to 55 degrees and lower, the fish should no longer be fed because their metabolisms begin to slow down and can no longer digest food. If excess food is retained in the stomach, it could cause gut rot. Also, avoid feed fish during any winter warm spells. This can cause serious harm to the fish’s immune system or outright kill them. Wait until consistent warmer water temps in the spring of 55 degrees to begin feeding the fish again.
  3. Maintaining an air hole can be low maintenance by using a thermostat controlled pond heater/de-icer. Some things you should not do are:
  • perform water changes during the winter,
  • bang and chop the ice to create a hole (can cause acoustic shock to fish),
  • and do not run the bottom drain (this will cause super cooling in the lowest depths of the pond).
Running the Waterfall:If the pump of the waterfall moves at least 2,000 gph, the waterfall can run continuously throughout the winter. Be careful of ice dams, check for evaporation.

Perennial Lilies:

After the first frost, cut back all foliage 4” above the rhizome. Move the plant to the deepest part of your pond. If the pond is at least 18” deep, all perennial lilies can be wintered in the pond. If the pond is less than 18” deep you must remove plants from the pond after the first frost, still cut them back and store them in a tub of cool water inside.


Water lettuce and hyacinths are extremely difficult to overwinter. Discard these floaters after the first frost.

Perennial Marginals:

If the pond is at least 18” deep, marginals can overwinter in the pond. After the first frost has killed the foliage, cut back the foliage and set the plant in the deepest part of the pond. If they are planted in planting pockets, cut back the dead foliage and leave them in the pockets.

Hardy Water Plants:Iris, rushes, cattail, sweet flag, ribbon grasses or other hollowed stemmed plants should be left in place. Do not cut back any foliage until spring. If these plants are cut back in the fall, the hollowed stems may fill with water and could rot the crown of the plants. Hardy marginal plants that are planted in a bog garden should be left in the garden all year. Winterizing potted marginal plants depends on the depth of your pond. If your pond is 18” or deeper, pots should be moved to the deepest end of the pond after the frost has killed the foliage. If your pond is less than 18” deep it is likely to freeze solid and the plants should be brought inside and set in a water tub.

Tropical Plants:

These plants must be removed from the pond before the first frost. They do best in a water temperature of 65-70 degrees. Umbrella palms, palms, papyrus, parrot feather, taro and canna are a few tropical plants that make nice house plants on a window sill or may be kept in a tub of water. Remove any dead foliage and all seed heads to help them make it through winter.

Oxygenators or Submerged Plants:

The oxygenators or submerged plants should be left fully submerged and weighted down at the deepest end of the pond. They must be kept under the ice line.

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