Winter Care Tips for a British Garden Pond

How a British Pond Behaves in Winter

A garden pond in winter is not a dead thing. It is a slow, quiet, crowded place. As air temperatures drop, water behaves in a way that works in your wildlife's favour: below about 4°C it becomes less dense rather than more, so the coldest water stays at the surface and the layer nearest the bottom holds steady at around 4°C. That slim band of relatively warm water is where frogs, newts, dragonfly larvae and a great many invertebrates sit out the coldest months.

Your job over winter is not to tidy everything up. It is to protect that arrangement, keep the water able to breathe, and disturb as little as possible. A little thoughtful maintenance in December and January makes a real difference to what emerges in spring.

Keep a Small Hole Open in the Ice

A pond that freezes solid across the surface traps gases produced by decaying plant matter and silt. Those gases build up and can be lethal to fish and amphibians. A single open patch, roughly the size of a dinner plate, allows gas to escape and oxygen to enter.

• Float a ball. A tennis ball or a purpose-made floating pond ball moved gently each morning keeps a hole from sealing over.
• Use a pan of hot water. Rest a metal pan of hot (not boiling) water on the ice until it melts through. This is the gentlest method available.
• Run an air pump. A small air stone placed near the surface keeps water moving and a hole open, and adds oxygen at the same time.
• Never smash the ice. The shock waves travel through the water and can injure or kill fish and hibernating amphibians, and the cracking releases trapped gas in one go.
• Never pour boiling water or add salt, antifreeze or de-icing products. All of them harm pond life.

If you have fish, keeping that hole open matters most during long cold spells, and an air pump is well worth the modest running cost.

Clear Leaves — But Gently

Fallen leaves are the main reason ponds turn sour over winter. As they break down they release nutrients, consume oxygen and produce hydrogen sulphide and methane. If you can net leaves from the surface before the worst of the cold, do so. A long-handled net, worked slowly, will lift most of them without clouding the water.

Once the pond has iced over, though, leave the net alone. Breaking through the surface to fish about in the water does far more harm than a few remaining leaves. If leaves are still collecting, and your pond is small, a light covering of netting over the surface can be lifted off in one go on a mild day.

Remember that some decaying material is valuable. A little leaf litter in the margins feeds the invertebrates that feed everything else. You are aiming for balance, not sterility.

Leave the Pond Bottom Alone

This is the single most important rule of winter pond care. Common frogs, toads, newts and a host of insects overwinter in the silt and mud at the bottom, often barely visible and sometimes partially buried. Dragging a rake or scoop through that layer in winter can kill them outright, and it also releases a cloud of trapped, oxygen-poor sediment into the water.

• Do not empty or deep-clean the pond between November and March.
• Avoid wading in. Footsteps stir up silt and crush anything beneath.
• Skip the sludge vacuum unless there is a genuine emergency, such as a build-up so deep that fish are gasping.
• Plan major cleaning for late spring, once amphibians have bred and left the water.

If you must remove something from the bottom, do it by hand, slowly, and check what you are lifting before you move it.

Fish, Plants and Equipment

Fish become sluggish below about 10°C and largely stop digesting food. Feed a wheatgerm-based diet while the water is still above 8°C or so, then stop entirely — uneaten food rots and fouls the water. If you keep a filter running for fish, do not switch it off for long periods; the bacteria in it need moving water. Insulate exposed pipes and check the pump intake is clear.

Marginal plants can be cut back, but leave seed heads and hollow stems standing — insects shelter inside them and birds will take the seeds. Submerged oxygenators can be thinned if they are smothering the pond, but leave plenty behind. Waterlilies can simply be left to sink.

Jobs for a Mild Day

When a mild spell arrives, it is worth a slow walk around the pond with a notebook in mind.

• Top up water levels with rainwater, not tap water, which contains chlorine and nutrients.
• Check the liner or edging for damage caused by frost heave.
• Clear any debris from the surface and from the surrounding grass.
• Check that heron netting or covers are still secure.
• Keep a shallow dish of unfrozen water nearby for birds and hedgehogs, which need to drink in hard weather.

Do not walk on the ice, and keep dogs away from a frozen pond. Enjoy the quiet version of your pond — it is doing exactly what it should, and come March it will repay you generously.