Preparing Aquatic Gardens for Winter

Aquatic gardens require a little attention in the fall to prepare them for winter conditions. The following tasks will help insure that the plants and fish survive the winter.

Remove dead plant debris:
Water lilies and other aquatic plants are vigorously growing plants that produce a fair amount of old, dying foliage, stems and flowers. Removal of the older deteriorating plant parts is a good cultural practice all through the growing season, but is especially important to do before winter. The accumulation of dead leaves, sterns and flowers causes murky water, stimulates excessive growth of algae, and stresses fish as it decreases oxygen levels. When the water’s surface seals with ice, the gases caused by the decomposition of this organic matter accumulate under the ice and can kill fish. After a hard freeze has killed water lily and other aquatic plant foliage, usually in late October, trim off and remove the debris.

Prevent tree leaves from falling into the aquatic gardens:
The accumulation of fallen tree leaves can be a more serious problem because of the volume of material. Tree leaves cause the water to develop an odor, become very dark colored and harm or kill the fish during winter. In early fall and throughout the winter, if practical, cover the pond to keel) leaves out. Some types of materials to use include leaf or bird netting, ½ inch hardware cloth or chicken wire.

Dispose of tropical plants
Tropical water lilies are perpetual bloomers, often right up to the last few days of their life. Unfortunately, they do not survive the winter outdoors. It is best to handle them as you would any other annual flower in the landscape and dispose of them at the end of the season. Because they are much more expensive than typical annuals, it is tempting to move them indoors for the winter. However, unless you have access to a green house, tropical water lilies usually do not survive well indoors. A nice tropical plant that is successfully kept indoors over the winter is the Umbrella Palm, Cyperus. Keep it wet and place it in a sunny location.

Move marginal plants into deeper water
The shelf along the edge of an aquatic garden is usually only eight to ten inches deep. In a very cold winter, plants left there may suffer extensive root damage from the ice. Lately, our winters in central Maryland have not been cold enough to do much harm to plants left in the shallower water of the pond’s shelf. To insure complete winter survival of marginal plants, move them in the fall down into the deeper part (18 inches or more) of the pond for winter.

Fish care
Goldfish and Koi do well over the winter in the pond as long as there is a water depth of at least 18 inches. Keeping the water free of excessive organic debris like leaves is important to prevent oxygen levels from becoming depleted. Stop feeding the fish as water temperatures drop to 50 degrees F (about mid-October). Fish that are accustomed to being fed daily will often engorge themselves with food. In the winter their digestion process slows dramatically and the undigested food decomposes in their stomachs and often kills them.

It is also helpful to keep a small area of the water surface free from ice to provide better air circulation into the water. This can be done using a stock tank or pond heater.

Disconnect and remove water pumps and statuary:
Don’t forget about mechanical features such as pumps, filter boxes and fountains. Ice can break concrete statuary, pumps and filter boxes if they become frozen in the ice. If the pump and filter box are in water at least 18 inches deep, they can be safely left in the pond as long as they are kept running. Running water will not freeze, and the circulation of the water will also aid in distribution of oxygen. It is still advisable to store expensive fountains or statuary indoors for the winter.

With a little preparation in the fall, an aquatic garden and its plants can survive adverse winter weather conditions in good condition. If your clientele needs more information about aquatic gardening, or any other type of gardening, refer them to the Home and Garden Information Center at 1-800-342-2507. Gardening experts are available daily, from 8:00 a.m. to 1:00 p.m. We also have a large assortment of Extension fact sheets and bulletins.

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