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How to Prepare Your Pond for Cold Weather

How to Prepare Your Pond and Water Garden for the Winter

Care for pond plants, fish, and pond health...
All summer long, you've enjoyed the tranquility of your water garden - beautiful foliage, sounds of trickling water and colorful fish eagerly awaiting a handful of food. The water garden didn't get that way by itself. You added the right kinds of plants and fish to create a balanced ecosystem.

The water gardens we create look beautiful and sustain life because we follow nature's rules. It's the same during winter months. Despite all outward appearances the pond is active even when the water is cold or frozen. Dead leaves, algae, insects and solid fish waste that have accumulated over the summer slowly break down during the winter months. This natural decomposition uses oxygen and produces hydrogen sulfide, a toxic gas. A build up of leaves and other debris can produce excessive hydrogen sulfide and at the same time, reduce oxygen to dangerously low levels. This can cause all of your plants and fish to die besides having a very nasty looking pond next Spring.

So, what should you do to provide a healthy pond during the winter?

First, remove all debris you can with a coarse net, which you should have been doing throughout the year. (To prevent more leaves from falling, drape a pond net over it.) Next, use a fine net or vacuum to remove any sludge covering the bottom. Since you're in there stirring things up a bit, you should change about 50% of the water, too. If your pond has a lot of "junk" at the bottom of it and is tinted yellow from dissolved organic material, make (2) 30-50% water changes a day or two apart. When you're pumping out the water, stir up the sludge and clean the bog and/or marginal shelves, etc. After everything is cleaned, start to fill with tap water.

Run the tap water through some Super Activated Filter Carbon which de-chlorinates the water while it's going into the pond. If you're real concerned about the chlorinated water, add some Ammo Lock to instantly neutralize the chlorine and chloramine in the tap water so it doesn't harm the fish (It also locks ammonia so if you ever have high ammonia levels in your pond, you can use the Ammo Lock). It is imperative that you get rid of the chlorine in the tap water or else it will kill your fish. Plants don't like the chlorine, either. Be sure not to put the chlorinated water in your biological filter such as bio-balls, lava rocks, filter pads, etc. as the chlorine in the water will kill your beneficial bacteria you've worked so hard at achieving in order to have a clear pond (and much more).

Over-wintering koi and goldfish in your pond

The metabolism of koi and goldfish is controlled primarily by water temperature. As the water cools, their metabolism slows down and they require less food and food with less protein. When fed high-protein diets in cool water, the excess protein is excreted as ammonia, and the fish can get sick and die from the high levels of ammonia. Eliminate high protein diets when the water temperature gets to 60-65°F and start feeding them "Spring and Autumn Fish Food" or those designed for cold water feedings. This type of fish food is better for the dietary requirements for the fish and won't pollute the water with excess ammonia.

Some gardeners continue to feed their fish until they no longer come to the surface and want to be fed, while others stop feeding the pond fish when the water falls below 50°F. Personally, I stop feeding them when they no longer come to the surface, which is usually around 50 - 60° F, but I feed them considerably less than what I normally do. Feed them about 20% of what you would in the summer and you should be fine. If the fish don't eat the food, of course, stop feeding them or else the uneaten food will only settle to the bottom and add to the overall nutrients in the water which feed unwanted algae and pond weeds some of the nourishment they need to grow.

For those of you who have ponds with fish and no plants, your fish can benefit from the addition of pond salt. Pond salt provides electrolytes to the fish and gives them a nice, soothing protective coating. It acts as a barrier from bacteria, fungus, and parasites that attack the fish. Use a .3-.5 % salt solution if you don't have any plants and only have fish, and about a 2% salt solution if you have both plants and fish. For those of you with large ponds, you can use a product called "Solar Salt". It is 99.6% sea salt and is used for water softeners. You can find it in your grocery store and I've even located it at Lowes. The main thing is that it does NOT have rust inhibitors or anything else added to it and is completely natural. It's essentially evaporated sea water where they've collected the salt deposits. You CANNOT use salt if it has additives added to it, like rust inhibitors. It comes in a 40# blue bag and costs about $5.00 and some change per bag. It's manufactured by Cargill. We use a .3-.6% salt solution for our koi ponds. This much salt ( .3-.6%) salt is ideal to use in the Fall and Spring when the fish's immune system is compromised and some bad types of bacterial strains and parasites are still active and growing. I will also tell you that some beneficial bacteria may die with a higher salt solution, so be careful on the amount you choose. You pond may not be crystal clear, but you fish can be healthier because of it. If in doubt, just check the ammonia levels in the pond. A 2-3% salt solution is a pretty safe bet. There are specific test kits that test for salt levels. They are referred to as salinity monitors. (Make sure your salt is totally dissolved and mixed throughout the pond before testing the water.)

After about 3 days of filling your pond with tap water, you can add some Microbe Lift/Autumn Prep. It is beneficial bacteria that has bacterial strains that work in cold water below 55°F (most of the beneficial bacteria on the market only work in water temperatures above 55°F). This will help to continue to decompose the organic matter in your pond during the Fall and part of the Winter. If frozen, it becomes active when thawed, so there's no need to worry about adding it if the water is very cold.

Will my fish freeze in my pond?

Well, if your pond is at least 30" deep and you live where you may get at most, a snowflake or two and that's all, you should be fine. If you live where there are harsh winters, you should have your pond at least 30" deep, if not deeper. If you're just creating a pond, do yourself a favor and make the pond 3-5' deep, and your fish will love you for it. Koi love deep water - you could have it 10' deep and they'd really love it. They need exercise from vertical swimming, so the deeper the better.

Anyway, after the water temperature has dropped into the low to mid 50's, bring your pump up closer to the surface of the pond so you don't disturb the warmer water below. Still keep the pump pumping, but just bring it up to a higher shelf or higher area in the pond. You can keep the pump on until the water temperatures are in the high 40's. From there you can turn off your pump and remove it from the pond as well as your filter. Clean them up for the winter and bring inside the garage. The reason why you don't want to keep your pump running is because the tubing which is most likely on the outside of your pond will start to have ice form within in it and will eventually freeze solid and cause your pump to burn out. When you remove the pump you will need to put in an ample size aerator in the pond. This will provide oxygen to the fish during the winter.

You may also need a pond de-icer which will keep an area of your pond's surface "open" and from freezing solid. This provides an opening for the toxic hydrogen sulfide gases from decomposing fish wastes, organic matter, etc. to escape and an entrance for oxygen to enter. We have a lot of information on our site as to which de-icer you should use. If you're reading this "a little late" and your pond's surface has already frozen, DO NOT go out and try to hack a hole in the ice. You just may hack into one of your fish! A neat little trick is to get a pan with a handle and attach a long string to it. Fill the pan with boiling water and set the pan on the ice. The heat from the pan of boiling water will melt a hole in the ice and you can retrieve the pan with the string! :o)

If you have a shallow pond or even a small preformed pond and you have small koi or goldfish less than 6" long, you really need to bring them either inside your home or you can keep them in an unused, untreated kiddy pool or aquarium set up in a cool basement or garage. All that is required is an small aerator to provide oxygenation. A nice, small but efficient aerator is one of our Small Pond Aerator. If outside in the garage, the fish may not need to be fed, depending on the water temperature (above 45°F or so). Put in about .3-.5% pond salt solution, too (start with .3% and then slowly add more up to .5%. You may need extra aeration during this time). This will give them a protective coating and help them adapt to their new surroundings plus eliminate some bacteria and fungus that can attack them. You should monitor the ammonia, pH and nitrite levels weekly especially if the fish are fed. (If you do plan on feeding the fish and IF they eat, you will need a filtration system and pump for the temporary pond/aquarium too so they don't die of ammonia poisoning). Small water changes, about 20% each month will keep the water in good shape until Spring. Koi are "jumpers" and will jump out of the pool/aquarium so be sure to cover it with the netting. This is a must or else you'll wake up one morning and find your dead koi on the floor beside your aquarium.

Some of you with small backyard ponds may not find it practical to bring the fish inside for the Winter. What you need to do then is have a pond deicer and an aerator in the pond. If your fish are less than 6" long and your pond is less than 30" deep, I would suggest a submersible deicer. The fish will need to huddle around the deicer to keep from freezing. The deicers will only turn on when the water reaches 40°F. It is thermo-regulated by the manufacturer. By having a deicer you're just keeping an area within your pond from freezing.

Those of you with large ponds, like the size of 1/4 of an acre or larger can benefit from an aerator during the winter months (and of course, summer months, too!). Aerators take very little energy and help to continue to decompose leaves and organic matter in the pond. You don't necessarily need a pond deicer to keep it open as there is a large amount of water in your pond. The proper size of aerator will help to keep an area of the pond 'open' as well. Aerators should ideally run 365 days a year.

Last but not least, over-wintering your aquatic plants...

Long after the impatiens have been pulled out, water gardeners are still hoping for that last lily to bloom before the snow starts to fly. We want to see just "one more blossom" before things get cold and yucky. Well, if you want your hardy plants to come back next year and make your water garden look beautiful again, this is what you should do:

  •  Trim bog and marsh plants such as papyrus, taro and cattails before it frosts. You can trim them to about 4" tall. Place in deep end of the pond, at least 30" deep.
  • Pull out the hard water lilies and trim off all the leaves and buds. I know, you don't want to take that last bud off, but you'll thank me next year when your lilies look gorgeous! Put them at the deepest end (at least 30" deep) of your water garden and let them "hibernate" there for the winter.
  •  Discard any tropical lilies as they are annuals and won't survive the winter or else you can try to save them by trimming 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. Keep them in a cool basement or garage and spray periodically to prevent drying out.
  • Discard inexpensive submerged plants, such as Elodea and Cabomba.
  • Discard floating plants such as water hyacinths and water lettuce. If you want to, you can try to bring them in but each plant takes up a lot of room and they need A LOT of light. Since they are inexpensive and multiply readily, it may not be worth the bother. The choice is yours. We consider them as annuals in Michigan and you should too.

If your pond is not at least 30" deep, the plants may not last the winter and you may have to buy new ones next year. What you can try to do is trim the plants as described above and bring them inside your home and put into tubs, aquarium or whatever you choose. They will need A LOT of light to stay alive. Try to place them where they will be exposed to the greatest amount of sunlight, if possible. Do some water changes every 2-3 weeks and still provide an aerator to them to keep the water moving or else have a pump and filter set up. Technically, you don't need the filter, but if you can somehow provide moving water, that would be good (the filter will come in handy if you bring your fish inside as well). If not, the water will get stagnant and smelly. If you're concerned about any particular plants, contact the store who sold them to you and see what they suggest for your particular climate.

Well, there you have it! All the instructions needed to properly over-winter your pond and ensure a healthy pond next Spring. As the old adage says, "an ounce of prevention is worth a pound of cure" and so we hope you'll use these "ounces' of information so you may have a healthy pond come next Spring!