Winter Care Guide for Garden Ponds

Part I: Winter Care of Pond Plants

Overall Guidelines. Fertilizing should stop about six weeks before first frost. “Hardy” plants should generally be allowed to go dormant for the winter. Wait until cold weather starts turning the plant’s leaves from green to yellow or brown, then trim off all the foliage, and follow one of the methods described below. “Tropical” plants, on the other hand, should not be exposed to night temperatures lower than 40o F., and should be moved indoors before their leaves start to change, and kept growing throughout the winter via the Bright Light method.

  • The Deep Pond method for hardy lilies and marginals. Wait until cold weather starts turning the plant’s leaves from green to yellow or brown, then trim off all the foliage, and simply lower the pot into an area of the pond where the water is at least 36″ deep. For best results, keep a small area of the pond free of ice by using a pump, air pump or heater (see general instructions for wintering pond fish). Move plants back up to their original shallower locations promptly in the Spring. Reported successes: Arrowhead, most Rush, Plantain, Hardy Lily, Iris, Sweetflag, Spider Lily, Glyceria, Sago Pond Plant, Vallisneria americum, Creeping Primrose, Wild Reed, Parrot’s Feather and Acorus.
  • The Flower Bed method for hardy marginals. Bury the plant, pot and all, in a flower bed, and cover with mulch. Return plants to pond promptly in Spring. Reported successes: Arrowhead, Pickerel Rush, Plantain, Sweetflag, Acorus, and Iris.
  • The Dark Indoor method for hardy and semi-hardy marginals. Place pot in a cool dark place, for example a root cellar, attached garage or cool basement. The idea is to keep the plant cool and dark enough to remain dormant. Plant should be watered regularly, or more simply immersed in a bucket of water. The plant still needs to “breathe”, so it should not be sealed off from air. Reported successes: Hardy Lily, Iris, most Rush, Plantain, Sweetflag, Canna and Longwood Canna, Cattail, and Wild Reed.
  • The Dry Root method for hardy or semi-hardy marginals. Unpot plant, then trim roots from tuber and rinse clean. Store tuber in cool dry place. Alternately, remove foliage only, then leave in dry, dark, cool place. Reported successes: Canna and Longwood Canna.
  • The Bright Light method for tropical marginals. Move plant indoors before leaves start to lose color. Keep in sunny window or under very strong fluorescent or metal halide lighting. Water thoroughly throughout the winter, or keep in kiddy pool or other indoor “pond”. Reported successes: Taro, Tropical Lily, Parrot’s Feather, Umbrella Palm, Papyrus and Water Poppy.

Part II: Winter Care of Pond Fish

Fish may be wintered indoors or outdoors, depending on the construction of the pond and the inclination of the hobbyist. They can also be “traded in” to us for credit (either immediate or for next year’s stock), but the law of supply and demand usually dictates very low prices paid on pond fish during the off-season.

Section A: Outdoors

A portion of the pond must be a minimum of 30″ deep, preferably 36″-48″, to protect fish from long cold spells. But even more dangerous than cold water is the buildup of toxic gases in a pond that is completely iced over for an extended period of time. Therefore, a portion of the pond’s surface should be kept open, to allow the pond to “breathe”, disposing of toxic gases and adding oxygen. This may be accomplished in one of three ways:

  • Heater / De-Icer. We now stock several reasonably priced de-icers that are safe for use in concrete, liner or even preformed ponds. The classic version is powerful (typically 1250 watts or more) enough to keep a small pond ice-free, or to allow a “breather hole” in a larger pond, and have been tested at down to -10 o F. They are preset to operate only when the water temperature approaches freezing to save electricity. Aquarium heaters are totally unsuitable for outdoor use; should they break due to harsh weather, live electrical wires are left lying in wet snow. In recent years, more energy efficient models of de-icers have appeared on the market. Please see Pond De-Icers for more details and our comparison guide.
  • Aerator. A large airstone operated by a standard aquarium air pump can also keep a small opening in the ice, at least during milder weather. Unfortunately, the precise placement of the aerator is hard to arrange and quite critical to its success: if it’s placed too near the surface, it will simply freeze in place during colder weather; if it’s placed too deep, it could actually chill the pond by bringing slightly warmer up from the bottom of the pond, and replacing it with the coldest water from the surface. The aerator should ideally be placed about halfway up from the deepest part of the pond and monitored frequently.
  • Water Pump. A water pump can also be used to provide an opening in the ice, but with the same limitations as an air pump. A submersible pump should be firmly mounted over the deepest part of the pond, far enough from the surface that it doesn’t freeze solid, and far enough from the bottom that it doesn’t circulate the lower layers of water. It also needs to be near enough to the surface to circulate the upper layers but not to allow pieces of ice into the intake. No filters other than possibly a coarse intake prefilter should be used (imagine cleaning a filter outdoors in February!), since any reduction in the flow rate will increase the likelihood of the pump freezing in place. Also, no fountain heads or waterfalls should be used; they create some attractive ice sculptures, but actually drain the pond in the process. Pumps should be inspected regularly; if they run dry or freeze solid, they will likely be destroyed.

Covering the pond. Covering the pond, or even a portion of it, can help protect it from extreme weather and drastically reduce the amount of electricity needed if a de-icer (heater) is used, but the cover must be raised above the surface of the pond to allow for gas exchange and an insulating layer of air. Ideally, a wooden frame would be built over the surface of the pond and covered with plywood, then insulating materials like Styrofoam, straw or even mulch. This could then be covered with a tarp or plastic sheet, to again trap in an insulating layer of air. They cover must of course be sturdy enough to withstand snow accumulation.

Feeding the Fish. The short answer to this is: Forget It, even if the fish look interested. In colder water, fishes’ digestive systems are sluggish. The best option for the hobbyist is to feed easily digested foods, especially those made from wheat germ, when the pond temperature drops below 55o F. Feeding should be stopped altogether when the pond temperature drops below 45o F.. Wheat germ foods should be again utilized in the Spring, when the water temperature is between 45o F. and 55o F., to provide an easily digested diet after the long cold winter.

Section B: Indoors

If wintering fish outdoors is impossible or unappealing, they may be moved indoors. This should ideally be done before the pond temperature reaches 55o F., to minimize any shock from adjusting to indoor temperatures. Fish may be kept in large aquariums, small wading pools, troughs or almost any other large non-toxic (galvanized metal is not suitable) container that will hold water. The container should be as large as possible, and have high enough sides or be fitted with a cover to keep fish from jumping out. It should be filtered and aerated (sometimes the pond filter will fit). Many hobbyists fill the indoor holding tanks with water right from the pond to ease the acclimation process and possibly shorten the “break-in cycle”. Fish should be fed regularly, but sparingly, since they are no doubt now in much more crowded quarters. A diet including Spirulina will help keep the fishes’ colors from fading due to lack of sunlight.

The “Empty” Pond. After removing the fish, the outdoor pond should be left nearly full, to counteract pressures from freezing and thawing ground. A few plastic milk jugs, inner tubes or other containers floated in the pond can be added to absorb some of the shock of the pond water freezing and thawing. Drain or remove any plumbing or tubing from the pond.