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In most of the UK, the first proper frosts arrive somewhere between late October and mid-December, and pond water temperature drops far faster than the air. By the time you can see your breath over the water, fish are already slowing down and heading for the deepest part of the pond. The work you do now — clearing debris, deciding what to leave running, sorting out ice management — is what carries your pond and its residents through to spring.
There is no huge mystery to it. Most winter losses come from three things: rotting leaves depleting oxygen, equipment left to freeze and crack, and well-meaning owners breaking ice with a hammer. Deal with all three and you are most of the way there.
Falling leaves are the single biggest winter problem in a garden pond. Once they sink they rot, consuming oxygen and releasing gases that can be trapped under ice. A fine net stretched over the pond in early autumn saves hours of work later, but carry on skimming weekly during peak leaf fall.
When you tidy the margins, cut back dying foliage to roughly 5–10cm above the waterline. Hollow-stemmed plants such as reeds and irises are worth leaving a little taller — insects and larvae overwinter inside them. Never cut below the waterline, because water can enter the crown of a marginal plant and rot it. Leave oxygenating plants alone; they will die back and sink naturally, and the stems give fish somewhere to shelter.
Opinions differ, and the honest answer depends on your setup. Moving water resists freezing and helps keep a hole open in the ice, which is genuinely useful. But a waterfall pumping near-freezing water from the bottom to the surface cools the whole pond, and in a hard spell that can supercool it — the opposite of what you want.
A good compromise for most garden ponds is to switch off the waterfall and main filter during the coldest weeks and run a small air pump instead. Site the air stone around 30–45cm deep rather than on the bottom, so it keeps the surface moving without stirring up the warmer layer where fish are resting. If you do keep a pump running, raise it off the bottom on bricks so it does not draw in muck and does not pull cold water through the whole pond.
If you turn equipment off, do it properly: lift pumps, filters and UV units indoors, drain and lag any external pipework so it cannot freeze and split, and store UV bulbs dry. A pipe full of water on a frosty night is a pipe you will be replacing in spring.
This is the rule that matters most. Never smash ice with a hammer, spade handle or boot. The shockwave travels through the water and can stun or kill fish, and cracks can damage the liner. Boiling water and salt are just as unhelpful — the first causes dangerous temperature swings, the second poisons the water.
Instead, aim to keep one open hole, ideally in the same place all winter. A purpose-made pond de-icer or floating heater does the job, as does a floating ball or a piece of timber, which absorbs the pressure as the ice expands. An air stone bubbling near the surface will also keep a patch clear. Plug any electrical de-icer into an RCD-protected outdoor socket.
Keep an eye on the water level too. Ice plus a low level can leave plants and fish dangerously shallow, so top up slowly with rainwater or dechlorinated tap water, trickled in so the temperature does not lurch.
Stop feeding fish once the water drops below about 10°C. In cold water their digestion all but stops, and uneaten food simply rots. A wheatgerm-based food during the shoulder season is fine if they are still active, but once they are torpid at the bottom, leave them be. Do not lift them, do not stir the silt, and do not add medications — most treatments are ineffective and can be toxic in cold water.
Frogs, newts and toads may be hibernating in the silt or tucked under stones at the margins, so tread carefully around the pond edge. Keep a gently sloping edge, a floating ball or a piece of timber in the water so that anything which falls in — hedgehogs, birds, the neighbour's cat — can climb out rather than exhaust itself.
Winter is not entirely dormant. On milder days, use the opportunity to check the pond rather than ignore it.
By late February, when the first warm afternoons arrive, you can start thinking about restarting filters, resuming light feeding and dividing overcrowded plants. Until then, the best thing you can do for your pond is leave it largely alone — clear, unfrozen and undisturbed.
Making Beck shares practical, down-to-earth guidance on garden water features: designing, building and caring for streams, ponds and waterfalls. for readers across the UK.
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