Why the Colder Months Matter

By the time the first frosts arrive, your pond has already done a year's worth of work. It has fed tadpoles, sheltered dragonfly larvae, given hedgehogs somewhere to drink and provided a mirror for the last of the autumn light. Autumn and winter are not a pause in that story, though. They are a different chapter, with their own tasks and their own risks. Get them right and you will be rewarded with clear water, healthy fish and a pond that wakes up in spring ready for another season of life.

The main jobs are simple to name. Keep leaves out, keep an eye on the fish, keep the water oxygenated, and above all keep your hands off the creatures that are trying to sleep at the bottom. Everything else follows from those four ideas.

Keep Fallen Leaves Out of the Water

A handful of leaves is fine. A blanket of them is not. As leaves break down they release nutrients that feed algae and blanketweed, and the decay uses up oxygen that fish and other creatures need. In a small pond, a heavy leaf fall can genuinely suffocate the life beneath the surface.

If you can, stretch a fine mesh net over the pond in early October, before the leaves really start to drop. Peg it just above the water so frogs and hedgehogs can still climb in and out. If netting is not practical, skim the surface every few days with a long-handled leaf rake or a pond net. Work in the afternoon, when any insects or newts caught in the debris have had a chance to move.

• Tip the contents of your net onto the grass for a day before composting, so frogs, beetles and larvae can crawl back to the water.
• Never empty the whole pond of silt in autumn. A thin layer at the bottom is home to overwintering invertebrates.
• Cut back dead marginal growth, but leave some hollow stems standing in bundles at the edge. They make excellent winter shelter.

Check Your Fish as the Water Cools

Fish metabolism slows dramatically below about 10°C. Their digestion practically stops, so the rich summer food they have been enjoying now sits in the gut and can cause serious problems. Switch to a wheatgerm-based food as soon as the temperature drops into single figures, and stop feeding altogether once it falls below about 5°C. Fish will graze on algae and natural pond life instead.

Cold water also makes fish more vulnerable to fungal infections and ulcers, often triggered by stress or poor water quality. Look at them carefully on mild, bright mornings when they are visible near the surface. Watch for white cotton-like tufts, frayed fins, red patches or fish that hang apart from the group. Catching a problem early in autumn is far easier than treating it in January.

Keep your filter or pump running through winter if you can, even at a reduced rate, and test the water for ammonia and nitrite every fortnight. Partial water changes of around 10 to 20 per cent on mild days will help dilute any build-up of waste.

Leave Frogs, Toads and Newts in Peace

This is the most important rule of the season. As temperatures fall, frogs and newts burrow into the silt at the bottom of the pond, sometimes half-buried in mud or tucked under stones and roots. Toads more often choose log piles, leaf heaps and compost bins on land. All of them are vulnerable to disturbance, and a frog woken from cold dormancy burns energy it cannot easily replace.

That means no pond vacuuming in winter, no dredging the bottom, no netting through the silt, and no moving any amphibian you happen to find. If you must work at the pond edge, do it with your hands and eyes rather than tools, and keep an escape route clear. A shallow ramp of stones or a piece of wood leaning into the water gives anything that falls in a way out again.

• Build a leaf or log pile near the pond in autumn and leave it undisturbed until April.
• Avoid draining or emptying a wildlife pond between October and March.
• If you find a frog indoors or on a path in cold weather, move it gently to damp cover nearby, but never into the pond itself.

Ice, Oxygen and Winter Water Quality

When a pond freezes over for days at a time, gases from decaying matter cannot escape and oxygen levels fall. Contrary to the old advice, never smash the ice with a hammer or boot. The shockwaves travel through the water and can injure or kill fish and amphibians. Instead, float a rubber ball or a piece of polystyrene in the pond as it freezes; simply lifting it out each morning leaves a clear hole. A pan of hot water rested on the surface will do the same job safely.

Keep an aerator or small pump running near the surface if possible, positioned so it does not stir up the silt. On snowy days, brush a little snow off the ice to let light reach the oxygenating plants below. Hornwort, water crowfoot and similar plants carry on producing oxygen in winter and are well worth their space.

Small Jobs for Mild Days

Save your bigger plans for spring, but mild, dry winter days are perfect for the gentler work. Thin out submerged oxygenators if they have become a solid mass. Clear fallen leaves from the surrounding borders so they do not blow back in. Check that any protective netting is still secure. Top up the pond with rainwater from a butt rather than tap water, which contains nutrients and chemicals you do not want.

Then step back and enjoy it. A winter pond has its own quiet beauty, and the birds, foxes and hedgehogs that visit it will thank you for the open water. Look after it gently now, and you will hear the first frog chorus all the sooner.