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Over-Wintering Your Pond

winter pond

Are your fish and plants ready for cold weather?

Right now, most of us are getting ready for fall by pulling up faded annuals, mulching perennial beds and raking leaves. Autumn clean-up comes almost instinctively to seasoned gardeners. But what about the water garden? Is your pond ready for winter? Even the most successful water gardeners sometimes wonder if the pond will “make it ” through the winter. Stop worrying.

Not all ponds need winter preparation.  Climate is a big factor when determining whether a pond has a real need for such seasonal maintenance.  Debris cleanup from the fall may be inevitable in any part of the country, but only ponds that experience ice cover over long periods of time will require winterization.  Let’s look at the steps necessary to over-winter the pond and discuss how it relates to a beautiful water garden next spring.

Too much of a good thing

This may seem contradictory, but you want to leave a little bit of debris in the pond when preparing it for winter. Some water gardeners net out the pond fish, completely drain the water and scrub out the pond, refilling it with fresh water. Frogs, tadpoles, snails and microscopic pond life need to burrow down into mud and leaves to survive the winter. Pond fish also hibernate on the bottom, settling in around a bed of leaves and mud. I remove about 90% of the leaves and silt that have accumulated over the summer. Leave the rest as
“bedding material.” You’ll be amazed at the diversity of pond life that emerges in spring. Keep in mind that tree leaves will continually blow into the pond as long as the water isn’t frozen. I recommend covering the pond with pond netting. This black pond netting is almost invisible and prevents tree leaves and debris from getting into the pond.

Pumps and filters

You won’t need to filter the water but it’s a good idea to keep it moving at the pond’s surface. Pond life needs oxygen even during hibernation. If ice covers the surface of the pond, oxygen can’t get in and toxic gasses can’t get out. Submerged pond pumps with fountains or waterfalls will oxygenate the water and keep a portion of the pond from freezing. If you live in an area that freezes solid I recommend using a pond pump and fountain to aerate the water. Set the pond pump on bricks about one foot below the water. This will prevent the pond pump from getting clogged with leaves and disturbing your pond fish while they are hibernating. If your fountain output appears to be diminishing, check the pond pump to make sure it is not clogged. Floating pond heaters are available to keep a small area free of ice. You can also use an air pump and diffuser stone to oxygenate and prevent ice formation. Even if the pond completely freezes over, the air pump keeps pumping oxygen into the water.

Maintenance is usually the determining factor in whether or not a pond owner keeps their pump running in the winter.  The primary maintenance responsibility at this time is to make sure there is enough water for the pump(s) to operate properly. During the winter months, the usual water supply options are now unavailable.  Outdoor water spigots and automatic water fill valves are turned off during the winter months to prevent pipes from freezing and cracking.  Therefore, pond owners who run their systems during the winter will have to find an alternate water source to replenish their pond.  Water can be supplied via a hose run from inside the house or multiple trips with a five-gallon bucket.  Generally speaking, it is not uncommon to have to go out once or twice a month during the winter to “top-off” the pond.

Pump size is important when determining a waterfall’s ability to operate during the winter.  A pump that provides at least 2,000 gph can be operated throughout the winter without a problem, as long as it runs continuously.  Moving water will usually keep a hole open in the ice around the waterfalls and in front of the pond skimmer.  However, repeated days in sub-zero temperatures may lead to excessive ice build-up and can cause the pond skimmer to run dry.  If the flow of water through the pond skimmer is unable to keep up with the pump because of ice build-up, it may be necessary to shut the system down. When you shut the sysem down remove the pond pump from the pond skimmer. Store it in a frost-free location, ideally submerged in a bucket of water.  The water around the pump housing will prevent the seals on the pump from drying and cracking. The system can be run again once the ice is melted and normal water flow is restored to the skimmer.  If the pump is attached to a water fountain, remove the fountain head, cleaning and storing it in a warm, dry place over the winter.  The pump itself may be used to keep an area of the pool ice-free.

NOTE:  If the pump is turned off during a heavy freeze, be sure to remove the check valve so the water drains from the pipe and waterfall filter..  Otherwise, the remaining water will freeze solid, and although this won’t hurt the pipe, ice may remain into spring, preventing the start up of the pond in the early spring.

WARNING:  There is nothing more breathtaking than a waterfall covered with ice formations and snow during the winter.  You must, however, be careful with ponds that have long or slow-moving streams.  In such cases, ice dams can form and divert water over the liner.

Over-wintering pond fish

The metabolism of koi and goldfish is controlled primarily by water temperature. As the water cools, pond fish require less protein in their diet. When koi and goldfish are fed high-protein food in cool water, the excess protein is excreted as ammonia from the gills. The microscopic organisms that make up the biological filter (and consume ammonia) also slow down in cooler water. Improper seasonal feeding can lead to a build-up of toxic ammonia, which stresses fish and reduces their winter survivability. When the water temperature drops to approximately 65° F, start feeding with Spring & Autumn Pond Food. This type of fish food is better suited for the dietary requirements of pond fish in cool water and won’t pollute the water with excess ammonia. Some water gardeners continue to feed their fish until they no longer come to the surface. I stop feeding my pond fish when the water falls below 42° F.

There is no need to worry about “frozen fish” if a section of the pond is at least 18 inches deep. Pond fish will seek the deepest part of the pond and over-winter there until the water warms in the spring. If your pond is less than 18 inches deep, the fish may freeze during a harsh winter. Check with your local pond supplier if you live in an area with harsh winters. Water gardeners with shallow ponds can keep their koi and goldfish in kiddy pools or aquariums set up in a cool basement or garage. All that is required is an air pump or small fountain to provide oxygenation. The fish are fed infrequently, if at all, depending on the water temperature. pH, ammonia and nitrite should be monitored weekly, especially if the fish are fed. Small water changes (20%) each month will keep the water in good shape until spring. Koi are “jumpers”-so be sure to cover the pool with bird netting!

Caring for aquatic plants

Long after the impatiens have been pulled out, water gardeners are still hoping for that last lily bloom. For some reason, we want to squeeze every leaf, bud and blossom out of our aquatic plants before winter. Unfortunately, cold weather often comes before we’ve trimmed the cattails or pruned the lilies. Wait too long and all those beautiful leaves will fall off and rot in the water. Trim bog and marsh plants such as papyrus, taro and cattails, before frost hits. Pull out the hardy water lilies and trim off all the leaves. Yes, even that last bud! Put all the potted plants into the deepest area of the pond to prevent freeze damage. Tropical lilies won’t survive the winter and are often treated as annuals, discarded in autumn. Some water gardeners have saved tropical lilies by storing them in peat moss. Trim off the leaves and roots and cover the rhizomes in a tray of damp (not wet) peat moss. The peat moss has antiseptic properties and helps inhibit rotting of the rhizome. The tray of peat moss should be kept in a cool basement or garage and sprayed with water periodically to prevent drying out. Inexpensive submerged plants, such as Elodea and Cabomba should be discarded.


Winter’s rest

The transition of summer to autumn does not mark the death of the water garden. It’s simply a time of rest for aquatic life. With proper care, the fish, hardy plants and tiny organisms that balanced your pond in the summer can survive the winter. Much of this care is simply an adaptation of the pond maintenance you’ve been practicing throughout the summer. Don’t wait for winter-get the pond ready now! You’ll have healthier fish, hardier plants and clearer water in the spring.