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Winterizing Your Pond

By Josh Spece

Water gardens are fairly low maintenance when compared to regular old dirt gardening, but there are some extra precautions you should take to make sure your water garden and its inhabitants survive our harsh winters with flying colors.

Fall is a very important time of the year when preparing your water garden for winter. It is best to have your pond go into winter as clean as possible. You should try to keep as many falling tree leaves out of your pond as possible by netting them off the surface of the water or stretching a mesh net over the pond. A wooden or pvc frame to stretch the mesh over is very useful. By having the netting tight the leaves tend not to weight it down and sink into the water. If the leaves lay on the net and are in the water, they can make your water tea-colored with tanic acid (NOT GOOD!). Also remove all dead flower heads and yellow/brown lily leaves. This should be done monthly during the active growing season to keep the pond clean and healthy. After a light frost you can remove all the water lettuce and water hyacinths, as they will turn yellow/brown and sink. Plant material that sinks to the bottom and rots will cause a deadly gas that can kill your fish.

In this area (zone 4) it is a risk to leave your lilies and fish outside in a pond less than 3’ deep. A severe winter could freeze a shallow pond almost solid and kill all your lilies and fish. If your pond is at least 3’ deep you can leave your plants and fish out all winter (place lilies in deepest area), but you will need some way for gas exchange to take place. Methane gas is produced by decaying plant material and is deadly to fish. Just because your fish aren’t very active, they still need plenty of oxygen in the water. You can provide gas exchange and fresh oxygen several ways:

  1. Keep your recirculating pump operating all winter. Set your pump on an upper level about 12" under the water, making sure the water coming out of the pump is breaking the water’s surface, or place an attached hose so that it creates a lot of surface disturbance. The splashing causes the gases to escape and lets oxygen back into the water. This is our personal recommendation!
  2. Place a tank heater in the pond to keep an opening in the surface. This can be very expensive to run and is usually only necessary in extremely cold weather.
  3. Place an air pump outside the pond and place an air stone in the pond to keep introducing fresh oxygen to the pond. This method will allow the pond to freeze over during extreme cold temperatures but still supply the badly needed oxygen.

You can use any combination of the above ideas for extra security.

NEVER BREAK ICE FORCIBLY!! Shock waves will stress the fish, injure their gills, and possibly kill them. Use hot water to melt a hole in the ice if necessary.

Leave fogs outside; they need to hibernate by burying themselves in the mud. If you let them find their own place to spend the winter they will be back next year.


If you decide to remove your fish for the winter there are a few things you should remember:

  • You will probably have to remove all pots from the pond and at least partially drain it while you are trying to catch the fish. They are fast and very good at avoiding the net.
  • When introducing your fish into the aquarium make sure that the water temperature of the pond and the aquarium are very similar and the filtration system is established. If you are on city water make sure you use Aqua-Safe to remove chlorine, chloramine, and ammonia, or let the water stand for 24 hours.

When placing koi and catfish in any kind of tank or container it must have some sort of lid because they will jump out. A floating block of styrofoam is also said to prevent koi from jumping. With goldfish and fantails there doesn’t seem to be a problem with them jumping. Fish in tanks need adequate oxygen and filter systems. When fish are taken indoors make sure to locate them where it is easy to change at least 1/3 of the water monthly, especially if it is over crowded and the fish are large. Guppies, tropical snails, and plecostomus should be brought in when the daytime highs do not get above the 50’s.


Tropical bog plants will need to be taken inside and kept actively growing. Tropical plants need light from the outdoors, next to south windows, or a minimum of four 4’ fluorescent tubes kept within a few inches of the plants. Make sure the tropical plants are kept wet. They don’t necessarily need to be setting in water, though. They are not growing as actively so they can tolerate a little dryer soil.

Tropical Plants: Four-leaf water clover, ginger, papyrus, pennywort (border line hardy), spider lily, star sedge, taro, salvinia, water hyacinths, water lettuce, thalia (Thalia delbata border line hardy), umbrella palm, and water cannas.

Once the hardy water lilies have gone through several frosts, they should be stored in a cool, dark area where it does not freeze and kept wet. To store properly, make sure the soil is moist, cover the crown with wet newspapers or cloth, and place in a garbage bag in a cool, dark area and check it at least once a month to make sure it has not dried out. Then, as soon as your pond is free of ice, put the lilies back in the pond (March or April). They will start growing sooner if put in the pond after the threat of extreme cold temperatures has past. If the lilies are kept in the house any longer, their growth and flowering will be slowed. It is best to over winter all hardy plants outdoors if at all possible!!

Tropical lilies need special treatment to over winter successfully. Before your pond freezes over, move your topical lilies, pot and all, to an area that will not freeze and forget it for about a month. During this time the soil is going to dry and the lily is going to form a small tuber about the size of a walnut. Once the lily has dried out, find this tuber. Place it is a jar or ziplock bag of barely damp peat moss and store in you refrigerator or an area that stays between 40 and 50 degrees. Check once during the winter to make sure the tuber doesn’t get too dry or has not rotted.

About the first of April, bring your tropical water lily tuber out of storage an place it is a container of warm water in a sunny window. Soon small shoots will begin to grow from the tuber. As soon as the big enough to easily handle and have a couple roots, remove them from the tuber and pot. Submerge the potted lilies so that a couple inches of water covers the soil. Do not place them in your pond until the water temperature stays above 70 degrees…about June 1st, here in Iowa (zone 4).

Completely submerged plants such as Curled Pond Weed and Hornwort are hardy. No other varieties will survive the winter.

After their leaves turn brown, hardy marginals (bog plants) can be trimmed back. Never cut plants with hollow stems off below the water level, because they will die if completely submerged (cattails, rush, and pickerel rush). All other plants can be placed on the bottom of the pond to over winter. The following plants should make it over the winter in ponds at least 3’ deep in zone 4: cattails, water iris, arrowhead, arrow arum, dwarf bamboo, bog arum, bog bean, bullrush, creeping jenny, goldenclub, lizard’s tail, variegated manna grass, marsh marigold, giant bur reed, flowering rush, horsetail, pickerel rush, soft rush, white rush, zebra rush, sweet flag, water cress, water celery, variegated water celery, water hawthorn, and water mint. Floating heart, thalia delbata, pennywort, and parrot’s feather if roots are below ice.

Frogbit is an unusual plant. It produces a small potato known as a resting bud or turion that stores food and become detached from the parent plant to pass the winter in the mud on the pond floor. If you remove the bottom mud from your pond in late winter, you will also be removing the resting bud. To over winter, collect some of the buds and store in moist soil in a frost-free place. Once new shoots form, return to pond or if left outside they will float up to surface.

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