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Before you pick up your spade and start digging, there are a few important details to decide - what size do you want your pond and what will you be lining it with.

Size

Your first consideration will be size. This will either be decided by the available space or cost (of the liner, which increases exponentially with size). Ponds can be any size you like, from a simple bird bath made out of an old sink or even an upturned bin lid upwards. Size needs to be considered in conjunction with material as plastic pre-formed ponds are only available in certain shapes and sizes and even flexible pond liners are only available up to a certain width. For a wildlife pond, aim for a minimum surface area of about 4 square metres (approximately 40 square feet) and a minimum of 0.5 metres (1.5 feet) deep, ideally 0.6 metres (2 feet) and if you have fish, which is not recommended in a wildlife pond, 0.8 metres (2.5 feet). This will give the pond enough water volume, surface area and depth to allow it to stay clear and not to freeze completely in winter.
 

Materials

Large ponds can be constructed with concrete or clay liners although this is an expensive and professional job. For a small to medium sized wildlife pond, there are two popular options, the rigid pre-formed pond and the flexible liner. Rigid ponds are made from a number of materials. The smallest and cheapest are made from fairly thin plastic. Further up the scale are glas fibre reinforced resin ponds and higer quality plastics. All bu the cheapest plastic ponds will last for many years but glass-fibre is brittle so it does need more careful handling than plastic. Rigid ponds appear at first site to be the simpler option. In fact they are not. They require very careful digging to make a hole just slightly larger than the pond shell. They then must be carefully in-filled around the sides with sand to ensure that all parts of the pond structure is firmly supported. If any part of the shell remains unsupported when the pond is filled with water, the immense weight of the water is certain to crack the shell. All but the largest (costing many hundreds of pounds) pre-formed ponds will not have much space for plants, especially deep marginals.

By far the simplest and best option for a wildlife pond is a flexible liner. You can then dig almost any shape hold you like and the liner will take on the shape. Flexible liners are much cheaper than the equivalent pre-formed pond but they do come in a variety of materials which vary considerably in price.The very cheapest are polythene sheets, just like a slightly thicker version of the sheets you use for decorating. They are thin, easily torn and should be avoided at all costs. Saving a few pounds at this stage will seem like a false economy when your established pond need a new liner! Next up the scale is PVC. A PVC liner is stronger than polythene but still easily damaged and it's quite tough and rigid and not easy to mold into natural curves without deep folds. By far the best choice is a butyl liner. These are made of a synthetic rubber material. They had a lovely soft rubber feel to them and feel extremely strong. They are virtually indistructable, you really would have to intentionally cut it. As it is more flexible it is much easier to force a butyl liner to take on the shape of your pond. Buytl comes in various thicknesses, which may be expressed in millimetres or as 'standard' or 'heavy duty' etc. The best advice is to buy the best you can afford. If you have to cut costs, skimp elsewhere, not on the liner. Consider making the pond just a bit smaller than planned if cost is an issue, the cost of a liner will drop dramatically, especially if you reduce the width rather than the length. A good buytl liner will have a 20 or 25 year guarantee compared with 5 or 10 for a PVC liner.

PVC liners to have their uses though. You could consider buying one to make a bog garden around your pond. Basically dig out a very shallow pond, line it with PVC and fill the soil back in. You'll end up with a very marshy area that is perfect for growing bog plants and moisture-loving marginals.

SITE

A sunny spot is best for a pond. Some shade is a good idea but avoid trees overhanging the pond as decomposing leaves will accumulate on the bottom and decompose to form toxic substances.

STYLE

Most wildlife pond designers will try to make their pond look as natural as possible. This means random curves. Try not to make the curves too tight or to create narrow inlets as this will waste your liner and it will also be difficult to form the liner around them. Think about the banks of the pond. In a natural pond some sides of the pond may have high steep banks well above the water level while other banks sweep gently down into the water. Try to emulate this by piling the soil you remove from the pond while digging to form banks. Make sure the banks are back-filled to stop them collapsing. Remember the obvious, that water is always level. The pond will only fill to the level of the lowest bank. When designing your pond, especially if it is on a slope, keep checking where the water level will be. A laser level is useful for this purpose. Rest it on the lowest bank and rotate it, keeping it level. Imagine the water at this level and adjust your banks until you are happy. Remember that your liner needs to go over the banks. If you want a particularly high bank, build it up on top of the liner after you've laid the liner and allowed the pond to fill. Don't attempt to build up a bank over the edge of the liner until the pond has filled otherwise it could stretch the liner.

SAFETY

If there's one thing a new pond attracts more quickly than wildlife, it's children. It goes without saying that a pond is potentially lethal to a small child. Even older children can quickly get into trouble when slippery surfaces combine with cold water. If young children are likely to be able to access the pond unsupervised, it is essential to errect a substantial fence around it with a lockable gate. A fence need not detract from the natural look of a wildlife pond. If done well, it can even enhance the look. A rustic pallasade fence (picket fence) for example, will highlight the pond as a feature as well as keeping young visitors safe without shutting off their view completely. Make sure you use suitable fence posts that are concreted into the ground.