The management of a pond during winter depends to a large extent on its climatic location. In the UK, seasonal climatic characteristics mean that maintenance routines must be altered to cope with the changes that take place during the colder months of the year. These include the shortened days and lower temperatures, particularly at night. As winter arrives, fish, other wildlife and plants all respond to this seasonal change in various ways. Fish will move to deeper areas of the pond for longer periods, plants stop growing and die back to enter their resting phase.
As winter progresses, ice may form on the water surface on a frequent basis. The depth of the ice may vary depending on the severity of the night time conditions and may not thaw during the daylight hours. Snow too may fall and cover the pond contributing further to the dark conditions within the pond. If snow does fall onto an iced pond, then scrap the snow away to allow light to penetrate the pond.
With falling temperatures, fish will progressively lose their appetite as they become less active in winter. Fish are likely to cease feeding if the temperatures drop to about 4oC and no attempt should be made to feed them. Generally though, during the typical UK winter month’s fish should be fed light, easily digestible formulations.
If your pond freezes over and remains so during daylight hours, make a hole in the ice to allow carbon dioxide to escape (carbon dioxide is toxic and therefore lethal to fish). The simplest way to make a hole in the ice is to pour hot water from a kettle on to the ice. It is advisable not to smash through the ice with a hammer or similar object, as this will send shock waves through the pond, which can stun fish.
Some Koi fish keepers now use pond heaters to maintain the pond water above 10oC (50oF) throughout the winter months. This keeps the pond ice-free and the fish active and feeding throughout the season. Fish kept under these conditions will continue to grow and not go into hibernation. It is believed by Koi experts that fish do not suffer by missing out on the period of hibernation that they would normally undergo in the wild or in a non-heated pond.
If your pond is used solely for fish, it is recommended not to switch off the pond pump and filter system but to run it normally or at a reduced rate. The high-quality of Butyl or Epayln rubber pond liners pond liners means they are not susceptible to frost damage. They remain pliable throughout winter. It is therefore advisable when planning a pond to use a good-quality pond liner vs cheaper, less flexible polythene liners which may suffer damage during the winter months.