Why Spring Is the Make-or-Break Season for a Pond

As the days lengthen and the water begins to warm, a garden pond wakes up all at once. Frogs and toads arrive to spawn, newts return from their winter hiding places, and the first insects start to stir in the shallows. At the same time, the plants that sat quietly through winter begin to grow, and any debris left in the water starts to break down much faster than it did in January.

That combination is why spring maintenance matters so much. A little work now, while the water is still cool and the wildlife is only just returning, sets you up for clear water and healthy plants right through to autumn. Leave it too late and you will be fighting algae, murky water and clogged pumps in the middle of the busiest growing season. The good news is that none of it takes long — an afternoon or two is usually plenty.

Clear Debris Gently — and Never Empty the Pond

The first job is removing the leaves, twigs and silt that gathered over winter. Use a soft rake or a net with fine mesh, and work slowly. Twigs and floating leaves can go straight onto the compost heap.

• Never empty a pond in spring to clean it. That is the single most damaging thing you can do. The water is alive with microscopic creatures, insect larvae, tadpoles and frog spawn, and refilling with tap water will shock everything that survives the draining.
• Leave the silt. A layer of sludge a couple of centimetres deep on the bottom is habitat, not dirt. Only remove it if it is smothering the whole base of the pond, and then take out no more than a third in any one year.
• Rest debris at the pond edge for a day. Anything you lift out will be full of small creatures. Leave it in a bucket or on a sheet of polythene beside the water overnight so dragonfly nymphs, water boatmen and the like can crawl back in, then dispose of what is left.
• Skim the surface twice in spring — once in early March and again in April — rather than doing one thorough job. You will disturb less wildlife and catch the debris before it sinks.

If you have a pump or filter intake, check the cage or sponge at the same time. A blocked intake is a common cause of a pump that seems to have failed when it is simply starved of water.

Divide and Replant Before Growth Takes Off

Marginal plants such as irises, marsh marigolds and rushes will have spread enthusiastically in their baskets. Spring, just as new shoots appear, is the ideal moment to lift and divide them.

• Lift the basket and use a sharp knife or a pair of old secateurs to cut the root ball into two or three sections. Replant the healthiest piece, in fresh aquatic compost, and pass the rest on to a neighbour or a school pond project.
• Refresh tired compost at the same time. Top-dress the basket with a layer of aquatic compost and a cap of gravel to stop it clouding the water, then add a slow-release aquatic plant fertiliser tab — ordinary garden fertiliser will leach into the water and feed algae.
• Thin oxygenators such as hornwort, water milfoil and elodea if they have filled more than about half the pond volume. Aim to keep roughly a third of the water surface clear so light and gas exchange can still happen.
• Check water lilies once the leaves reach the surface. Divide them only if they have outgrown their basket or the flowers have become sparse; many lilies are happiest left alone for several years.

Wake Up the Pump, Filter and Pipework

If you switched off your pump over winter, restart it once the risk of hard frost has passed and the water is consistently above about 8°C. Fish and other pond life become more active as the water warms, and their oxygen demand rises with it — a filter that has been sitting idle needs time to build up its colony of beneficial bacteria before the load increases.

• Clean the impeller and remove any grit or plant fragments. A gentle rinse in a bucket of pond water is all that is needed; a pressure washer or tap water will strip the good bacteria from your filter media.
• Rinse filter sponges in pond water only, squeezing them out until the worst of the sludge is gone. Replace any media that has crumbled or gone brittle.
• Check pipework and unions for splits and leaks, and make sure any hose is not kinked or buried under new plant growth. Secure cables so they cannot be nibbled by wildlife or tripped over.
• Consider adding an air pump or a small fountain if the pond is shallow or heavily stocked. Extra surface movement makes a real difference on warm, still nights.

Test the Water and Top Up with Rainwater

Water that looks clear is not always healthy, so a simple test kit is worth keeping. Check ammonia and nitrite first, then pH and carbonate hardness (KH). Ammonia and nitrite should both read zero; if they do not, cut back on feeding fish and let the filter catch up. KH matters because it buffers against pH swings, and a low reading is common after winter rain. Most kits come with a means of raising it, usually in the form of a gentle mineral buffer.

Spring evaporation and winter rain leave most ponds lower than they should be, so top up gradually — and use rainwater wherever possible. A water butt filled over winter is ideal, and it is free of the chlorine and chloramine that make tap water harsh for pond life. Add it in stages rather than all at once, so temperature and chemistry do not swing wildly. If you must use tap water, add a dechlorinator and run it in slowly through a hose with the end above the surface.

Finally, walk the edges and look at the pond as a whole. Is there a shallow beach where hedgehogs and frogs can climb out? A small ramp of stones or a piece of roughened wood leaning into the water will save lives. Leave a patch of longer grass nearby, and pile a few logs or stones in a quiet corner — the amphibians you are encouraging this month will repay you all summer with slug patrol in the borders.