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What should I do if my pond has frozen?
Preparing for British Winters
The British weather is predictably unpredictable, so in some years the garden pond may only have thin ice cover for a few days, whilst in other years, thick ice and snow can blanket ponds for weeks at a time. For this reason there is no guaranteed best approach for winter preparations. Preparations may be over-the-top in a mild winter, or insufficient in a harsh winter.
Fountain and water feature pumps
If icy weather is forecast, it is usually best to turn off fountains and pumped ornaments. Check any instructions with self-contained water features, as very shallow features (and those in materials that might be damaged by ice) may need to be drained and the pump stored inside. In general, as long as submersed pumps are below the level of any ice, they should come to no harm. ©www.watergardensolutions.co.uk
Ice not always a problem
If the pond entered the winter in a healthy state, without an excessive build up of decaying leaves and debris on the base, and with moderate stocks of fish, there should be few problems for pondlife. Make sure that any submersed pumps are kept deeper than possible ice levels (but above debris on the pool base).
Cold water usually has a good amount of oxygen dissolved in it, and any fish and wildlife, sluggish in the cold, will be using up less oxygen. In these cases the pond inhabitants should be able to cope with the surface being sealed by ice for a few days without coming to any serious harm.
Pumps and filters
During shorter spells of freezing, if you have a pump or filter still running, leave them on. The water movement will help to keep an area free of ice; will maintain biological filter organisms; and will circulate the water helping to keep oxygen levels high. However, avoid excessively strong water currents as these can chill the water and may upset fish.
Prolonged cold
If your filter/cascade pump can be kept running, this should provide sufficient circulation and aeration. If you have no pump running, and the surface stays completely sealed for more than a few days, problems might arise for wildlife in the pond. The oxygen levels may start to fall, and dissolved waste gases may start to build up in the water. This is especially a problem where the pond is heavily stocked with fish or frogs; has a lot of debris on the base; or has snow lying on the ice, stopping light from reaching underwater plants.
If you have no water-pump, an option is to use one of the small floating pond-heating units or a small air-pump bubbler to keep an area free of ice and circulate oxygenated water from the surface. The open water will also be valued by birds and other garden wildlife. If you don’t have this equipment, keeping a hole open in the ice is still beneficial. Don’t smash the ice, as the shock waves can upset fish, and jagged ice can damage liners. Melt a hole by carefully pouring on water from a kettle (avoiding pondlife), or resting a pan of hot water on the ice. Check that the hole is kept open at least twice a day. Note that Koi can be weakened by long periods at very low water temperatures (< 4 degrees C), and extra precautions may be required
Pumps, filters and UV units are less likely to suffer frost damage if they are kept running. However, in those cases where prolonged freezing (lasting many days) starts to ice up waterfalls (possibly causing water loss), you may be forced to turn pumps off. If so, drain exposed units down, otherwise water inside the units will freeze and could split the casings. Note that any biological filter which is turned off or drained in the winter can take three to six weeks to become active again when they are restarted in the spring.
Pond damage?
Flexible liners and plastic/GRP moulded ponds are rarely damaged by ice pressure, but concrete ponds and stone/terracotta features are more vulnerable. Placing a floating ball on the surface makes little difference. Insulating covers may help a bit, but vulnerable containers are better drained or moved to a sheltered area.
After the ice has gone
If the pond smells stale after the ice has melted, carry out a partial water change using tap water conditioner if necessary.
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