Why a frozen pond is not the disaster it looks

Come the first hard frost, many of us look out at a sheet of ice over the pond and worry. In truth, a frozen surface is perfectly normal and most of your pond life is already tucked up and waiting it out. Frogs will have buried themselves in the silt or found a damp corner under a log, newts are sheltering in the leaf litter at the bottom, and dragonfly larvae are sitting quietly in the mud. The creatures that suffer are not the ones that freeze — they are the ones that suffocate.

The real danger is a pond sealed tight by ice for weeks on end. Decomposing leaves and plant material on the bottom use up oxygen, and if nothing can get in, levels drop fast. Trapped gases from the mud below can't escape either, and that combination is what kills fish, frogs and insects. So your main winter job is not to keep the pond warm. It is to keep it breathing.

Keep a hole open in the ice

Your priority through any cold spell is maintaining at least one patch of open water. It doesn't need to be big — the size of a dinner plate is plenty for most garden ponds — but it needs to stay open.

• Float a ball. A tennis ball or a purpose-made pond float bobbing on the surface will keep a small circle of water moving and often stops ice forming across the whole pond in the first place.
• Melt rather than smash. If the pond has already frozen over, stand a saucepan of hot water on the ice and let it melt a hole through. Never take a hammer or a boot to the ice: the shock waves travel through the water and can stun or kill fish and amphibians resting below.
• Never add salt, antifreeze or de-icer. All of them are toxic to pond life, and a surprisingly small amount will do real damage.
• Keep the hole clear. Check it every morning during a cold snap, because a small opening will skin over again overnight.

If you have a pond pump or filter, running it through winter at a low rate in a way that disturbs the surface is one of the simplest ways to keep a gap open without any daily effort. Angle the outlet so it ripples the water rather than stirring up the silt.

Look after the frogs, newts and insects

Amphibians overwinter in the most unlikely places, and a tidy-up at the wrong time of year does more harm than good.

• Leave the leaf litter alone. Piles of damp leaves around the pond margins are winter bedrooms for frogs, toads, hedgehogs and a whole host of insects. Resist the urge to clear them until spring.
• Don't tidy the borders. Hollow plant stems, log piles and stacked stones all provide shelter. Cutting everything back in November strips away the cover that wildlife needs to survive the coldest weeks.
• Watch the pond edges. Frogs sometimes surface on mild winter days and can become trapped under ice if they can't find a way out. A gentle slope or a half-submerged log at the margin gives them an escape route.
• Leave a shallow dish of water. On frosty nights, a ground-level dish near the pond that you keep thawed gives birds and mammals a drink when everything else is locked solid.

What to do about plants and pumps

Hardy native marginals such as rushes, sedges and marsh marigold will shrug off the cold, but a few plants need thought. Tender or borderline-hardy species in pots are best moved to the deepest part of the pond, where the water at the bottom stays above freezing, or lifted into a sheltered spot. Tropical and half-hardy plants should come out altogether and be overwintered somewhere frost-free.

Cut back dead foliage from marginals, but leave the stems of anything hollow — they're valuable shelter. If you have oxygenators, don't be alarmed when they die back and vanish; they're resting on the bottom and will return in spring.

As for equipment, most pond filters can be switched off once the water drops below about 5°C, when the fish stop feeding properly and the bacteria in the filter go dormant. Keep a pump running if you can, purely for surface movement. If you have fish, stop feeding them in earnest once the temperature falls below 10°C; any food they don't eat will rot and spoil the water.

Cleaning, feeding and other jobs to postpone

Winter is a season for doing less, not more. Netting out every last leaf sounds diligent, but a certain amount of leaf litter on the bottom is part of a healthy pond, and the sludge is full of the tiny invertebrates that feed everything else. Scoop out the bulk in autumn to stop it building up, then leave the rest.

Don't empty the pond, don't scrub the liner, and don't repot plants — all of that disturbs hibernating wildlife and can leave it exposed to hard frost. If your pond has a build-up of blanket weed or duckweed, leave it until spring. The same goes for any major pruning or dredging.

If you do want to do one extra thing, a bundle of barley straw floated in the pond is a traditional way to keep algae in check as the light returns, and it costs you almost nothing in effort.

A simple winter routine

None of this needs to take more than a few minutes a day. Each morning during a cold snap, glance out of the window and check that your open patch of water is still there. Once a week, clear any floating debris and check your plants haven't been lifted by frost heave. Once a month, look over the margins and make sure the leaf piles and log stacks are still intact.

Do that much, and your pond will come through the winter with its frogs, newts, beetles and larvae ready to wake up. The first mild day of February, when the frogs start moving again, is one of the best rewards in the garden — and it's one you've earned by doing very little at all.