How to make a pond

Why make ponds?

This century has seen the loss of about three quarters of Britain's ponds, along with the populations of wetland plants and creatures they supported. In making a pond you are literally building an oasis - for frogs, toads, newts, dragonflies and the like - in our modern desert. A pond is a feature of great beauty, which will give you endless pleasure as you watch its wildlife come and go. It is also an invaluable aid to understanding the workings of nature - no school should be without one!

What kind of pond?

Natural ponds come in many shapes, sizes and locations, each suiting a different plant and animal community, but your garden, school or nature area pond will probably be most useful if it is unshaded and holds water constantly. Choose a sunny spot, away from trees and near a water supply.

The most straightforward way of holding water in is usually to lay a butyl or other flexible liner. (Advice on using clay, concrete or other linings can be given separately.) To work out the size of liner needed for the size of pond you have in mind, use this formula: (length plus twice maximum depth) by (width plus twice maximum depth).

Digging and lining

Your deepest point need be no more than one metre - in fact, most of the pond's wildlife activity goes on in the shallows. Make this point even shallower in the case of a small pond, otherwise the sides will be too steep. Place the deep point off-centre, shaping the sides with gentle contours, gradual slopes and perhaps shelves.

Dig the hole a few inches deeper than the pond to allow for padding - newspapers, carpet, sand or pond liner underlay - and remove anything sharp. Lay the liner on top of the padding, cover with a two-inch layer of subsoil, and trickle water into the pond over a plastic sheet to avoid disturbing the soil. As the pond fills, the weight of water will push the liner into the exact shape of the hole. Now you should bury the edges of the liner - there's no need to trim off the excess, as the buried liner will serve to impede drainage and encourage damp-loving plants around the pond.

Stocking

Leave the pond to settle for a few days, then pour in a bucket of mud and water collected (with permission) from a good established pond. This will help to start off a balanced living community. Introduce plants at this stage as well, including species suitable for each depth. Don't use non-natives - such as Canadian pondweed, parrot's feather, floating fern (Azolla) and swamp stonecrop - as they are not as useful to wildlife and they have a habit of spreading to other ponds. The Trust can supply a list of suitable plants.

It's probably OK to move frog spawn to a new garden pond from another nearby garden pond, but we would discourage spawn movement in all other cases. The danger is that undesirable plants, creatures or even diseases will be passed around in this way. If your pond is suitable, amphibians should find it sooner or later. Don't introduce fish! They only occur naturally in very deep (or stream-fed) ponds, and will reduce the wildlife value of any pond into which they are artificially released.

Managing

If you want to top up the pond (remember that, in nature, pond levels rise and fall, and that seasonal drying out of ponds is a good thing for some species), try to use rainwater. Otherwise, hold tap water in buckets or barrels for a few days to allow its chlorine to escape, or add very small amounts at a time.

Algal blooms might be a problem at first, but, if you have followed the rules above, your pond should soon reach a natural balance. In the meantime, scoop the algae out if you can. As with any weed clearance, leave it on the pond's edge for a couple of days, to allow creatures to hop back in, but then remove it from the site so its nutrients don't overfeed the water.

Managing your pond should be very easy. Keep marginal plant cover to about a third of the pond's surface, leaving the other two thirds for submerged weeds and bare mud. Silt normally takes many years to fill a pond - you shouldn't need to clear any out within your lifetime. Don't ever "clean out" a pond as this will destroy the wildlife community it has developed.

This guide has been written by Mark Nicholson of the Cornwall Wildlife Trust.

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