Why spring is the best time to tackle a neglected pond

The window between late March and mid-May is the sweet spot for a pond revival. The worst of the frost has passed, the water is warming, and plants are just beginning to move. Leave it much later and you will be wading through a jungle of soft growth, disturbing nests and trampling the very creatures you are trying to help.

There is one important caveat: if your pond still holds frogspawn or newly hatched tadpoles, wait. Spawn takes roughly two to three weeks to hatch, depending on temperature, and tadpoles are at their most vulnerable in those first few days. If you can see jelly or wriggling black commas, hold off until they are mobile and dispersed around the pond margins. A pond cleaned in early June is still not a disaster, but one cleaned in April, with the spawn, is.

Before you start: check who is living in there

Put on your wellies, stand still, and watch for five minutes. Ripples, bubbles and sudden movement will tell you a great deal. Then take a closer look at the shallows and under the plant cover.

• Frogs and toads shelter in the damp soil at the pond edge and often sit tight under stones and vegetation.
• Smooth and palmate newts hide in silt and among plant roots. They are common in UK garden ponds and easy to miss.
• Great crested newts are protected by law, along with their breeding sites. If you find one, stop work immediately and take advice from an ecologist before doing anything else.
• Dragonfly and damselfly larvae, water boatmen, leeches and snails all live in the silt you are about to remove.

Have a large bucket of pond water ready, plus a second container of clean rainwater. Any creature you accidentally scoop up should go straight into the bucket, in the shade, and be returned as soon as you have finished.

Dealing with silt and debris

Silt is not the enemy. It is habitat. The mistake most people make is stripping a pond back to bare liner in one heroic afternoon, which destroys the invertebrate population and releases a soup of nutrients that feeds algae for months.

Work to a rule of no more than a third of the total silt removed in any one year. Use a net or a rake rather than a spade, and lift gently from the surface layers rather than digging into the bottom. Spread anything you remove on a sheet of tarpaulin at the pond edge, in a shady spot, and leave it for 24 to 48 hours. Small creatures will crawl back downhill and into the water of their own accord. Then compost what is left.

If the pond has a liner, avoid standing in it. Work from the bank, kneeling on a plank or a wide board to spread your weight, and never walk on the liner in cold weather when it is least flexible. Keep your feet out of the pond altogether where you possibly can.

Dividing and refreshing plants

Spring is the right time to lift and divide, just as new growth is showing but before the plants have spent their energy. Crowded oxygenators such as hornwort and native water starwort should be thinned back to roughly a third of their mass, with the healthiest shoots replanted or returned to the water in weighted bunches.

Water lilies need lifting every few years. Cut away the old, woody rhizome with a sharp knife and retain the youngest, firmest growth. Repot into a basket lined with hessian, using a loam-based aquatic compost that is low in nutrients. Never use ordinary garden soil or multipurpose compost, which will leach nutrients and trigger algae. Top-dress with washed gravel to stop the compost floating away.

Marginals such as yellow flag iris, marsh marigold and ragged robin benefit from a hard tidy in spring. Cut back dead top growth, divide the clump and replant one healthy section. Remove any dead leaves floating on the surface rather than leaving them to rot down.

Pumps, filters and equipment

If you run a pump or filter, it will not have been doing much over winter and will need a proper look before the growing season.

• Lift the pump, clean the impeller and check the intake is not blocked with blanketweed or leaf litter.
• Rinse biological filter media in a bucket of pond water, never tap water, which will kill the bacteria you have spent a year cultivating. Clean only half the media at a time.
• Check all cables, connections and the outdoor socket. Everything should run through an RCD.
• Inspect the liner and the edges for damage while water levels are low.
• Top up with rainwater from a butt wherever possible. If you must use tap water, use a conditioner and add it slowly.

Leave a little mess behind

The tidiest pond is rarely the best pond. Resist the urge to clear every leaf and every stem. A shallow beach of stones at one end gives hedgehogs, frogs and beetles a way in and out, and a simple ramp of roughened wood or chicken wire will save animals that fall in during the night.

Leave piles of stones and logs near the pond edge for shelter, and hold back from cutting all the marginal growth at once. Hollow stems left standing into late spring are used by emerging insects and nesting solitary bees. By midsummer you will have a pond that looks cared for rather than scrubbed, and a queue of wildlife that has moved in to say thank you.