We don’t need any reminders that we are experiencing a bitterly cold winter, but for this reason we do need to remember that as a pond owner we have tasks to do during the winter months to protect our pond against the freeze.
Firstly, it is important that a pond needs to be ventilated when it freezes over, which no doubt most if not all have this month. To ventilate a pond, hold a saucepan of boiling water on the surface until the ice melts. After creating a hole, if possible, drain off a little of the water so that an air cavity is formed below the sheet of ice. Or, install an electric pond heating element with a float attached to keep it at the surface.
Prolonged freezing at the surface prevents the escape of noxious gases especially in shallower ponds if there is a deep sediment of organic plant debris. An ice covered pond will prevent submerged plants from producing enough oxygen to compensate for this and fish may suffer as a result.
A pond pump can also be used to provide an opening in the ice. 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, 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. Pond pumps should be inspected regularly; if they run dry or freeze solid, they are likely to get damaged.