Before you get started

Regardless of the type of pond you’re planning, there are some guidelines that apply to them all.

garden pond in landscape

Site your pond where it will receive at least six hours of sunlight a day if possible. This is important for plants such as waterlilies as well as providing the warmth and energy that fuels biological processes. As well as shade, trees also mean leaf fall and roots that complicate digging and are best avoided.

Choose a level site. Water will always find its own level, and this can lead to problems if you garden on a slope. Consider the lie of the land and don’t forget that a raised, or semi-raised pond can be constructed and incorporated into a terrace if needed. If the ground does slope slightly, a bog garden makes use of any overflowing water and gives the opportunity to grow some very attractive plants.

Think about utilities. If your garden is large, consider the practicalities of installing electrics or how wastewater will be handled in the case of koi ponds.

Safety first. It’s important to remember that water can be dangerous to unsupervised small children, so consider fencing, a raised pond or the specialised barrier products that will prevent any accidents from occurring.

What type of pond is right for you?

Starting at the smaller end of things, wildlife ponds don’t need to be big but they do work better if they’re free of fish. This means that a small offcut of liner or a budget preformed pool is an option but if your dreams run to bigger things then you’ll be amazed at the number of species you can attract. Wildlife ponds don’t need to be scruffy but do work best as part of a mosaic of complementary habitats such as long grass, log piles or dense planting that provides cover for visitors such as frogs. A small wildlife pond complements a fishpond nicely and provides sanctuary for garden visitors such as newts that don’t fare as well with fish as neighbours. Find more information on wildlife ponds here (https://www.fishkeeper.co.uk/stories/go-wild-in-the-garden-2). 

It’s a very broad term but most people think of a typical ornamental garden pond as the sort of feature that houses colourful fish alongside pond plants. Unlike a wildlife pond, a fishpond needs to be large enough to cater for the needs of permanent residents in all four seasons. To remain stable in the heat of summer and the cold of winter, it’s important to provide a depth of 60 cm (24”) in around half of the pond’s footprint. As this is a great way to increase the water volume without taking up extra space, increasing depth is a good way to ensure you have extra carrying capacity for the fish population.

A world away from the small wildlife pond, the dedicated Koi pond is more like a huge outdoor aquarium. To provide maximum water volume in the allotted space, these tend to be deep. A depth of 1.2 metres (48”) or more is needed for koi and this is where planning is important – most koi keepers tend to extend their ponds as they realise that their pets get better with age and size. Far better to go large at the start and plan on having a number of 60cm fish that need a lot of filtration.

The final option for fish keepers who like to take their hobby outside, seasonal feature ponds provide summer accommodation for fishes that will spend the winter indoors. These can make a great addition to patios and other outdoor areas where you’re likely to spend recreational time and are a great option for fancy goldfish or temperate species that will thrive outdoors in the warmer months.

Designing your pond

Once you’ve considered the type of pond you’d like and found the right spot, think about how the size and shape relate to other aspects of the garden. Would a formal design with straight edges work best, or perhaps informal sweeping curves would fit the mood of the garden better? Rectangular shapes are the most efficient when using a flexible pond liner but look less natural unless softened by extensive planting. Pond edging can often make or break the look of the finished project, consider the options and how they’ll fit with the surroundings.

To get a feel for the size and shape, lay a hosepipe in the planned area and see how it looks. View it from all angles and take some time, it’s a lot easier to change the design at this stage before you’ve even lifted a spade.

For some projects, hiring a mini-digger may be a sensible option – check site access and consider what to do with the soil removed from the excavation. For large koi ponds, this might need to be removed from the site if it can’t be used around the garden. Luckily, most ponds aren’t full-scale civil engineering projects.

If you’re planning to use a flexible liner, you’ll have the most design options but remember that sharp corners can be hard to line without creating a lot of pleats and folds. For formal pools, rubber liners can be box welded to give a right-angle without distortions in the liner, otherwise, keep curves gentle.  As well as deep areas, your design should include shallower shelves for marginal plants which like to have their roots submerged but their leaves above the surface. These will help to provide a means for animals to come and go but a gently sloping beach will be of great benefit to animals such as hedgehogs which can drown in steep-sided ponds.

Once you’ve dug your pond, it’s time to double-check your measurements and source the liner. To calculate the size required, measure the length and width before adding twice the maximum depth to each (L+2D x W+2D). To allow for edging and any minor errors in measurement, it’s sensible to add 1m on each side. As an example, a pond 3 metres long, 2 metres wide and 1 metre deep gives a 6x5m liner. Often the surplus needed for edging can be found by rounding up from an unconventional measurement. As an alternative, preformed ponds make the design simpler and come ready to install.

Check each side of the new pond with a spirit level to avoid problems having to disguise a ‘high end’ later and if you’re using a preformed pool, check that the base is level too. Whatever material you’re using it’s important to check for stones and other objects, as these can either puncture a flexible liner or damage a rigid one, once the weight of water acts upon the pressure point. One factor that might become apparent at this point is a high water table, this might mean that your potential pond has water in it before the liner is installed. In this instance, it’s best to pump this away if possible. Once the pond is filled, the weight of water on the liner will usually keep it in place. If your design in sympathetic, you might also wish to consider a semi-raised installation which involves building a wall to support the sides of the pond above the soil level – this approach works very well with rigid preforms which have built-in strength

With the excavation free of sharp objects, prepare the surface for the liner. Rigid pools are best installed on a layer of sand to support them evenly and make levelling them easier. Flexible pond liners can also be laid on a bed of sand but are better protected by specially woven underlay which resists puncture by sharp objects.

Before installation, place rubber or PVC liners in a warm place to ensure maximum flexibility and reduce the tendency to form creases. Check the surroundings for sharp objects too, as large liners are often easier to open out beside the hole before positioning them. With the underlay in place, lower the liner into the hole and run a hose to start filling the pond – the weight of the water will help settle the liner, which can be pulled from all sides to keep it as smooth as possible. If you’re installing a wildlife pond, you may wish to cover the liner with a layer of underlay to give it more protection. You can then add a layer of silver sand or soil above this to better mimic a natural pool. Older references will often stress the importance of protecting PVC liners from sunlight, this is more of an issue with very low-budget liners of old, which lacked protection from UV. Quality pond liners tend to come with long guarantees against material failure.

With the weight of the water to help, continue pulling the liner as it fills and you’ll soon be faced with the decision of how to finish the pond edge. This is always the thing that makes or breaks the final effect, and some options are easier than others. Traditionally, slabs or crazy paving were used, and these materials might be appropriate to blend with the rest of the garden. Timber can be a good alternative, and both work well in formal settings. Alternatively, more naturalistic margins can be made using bog pockets (where plants will mask hard edges), gravel beaches or turf laid over the liner edge. These are all good choices for wildlife ponds, but some will wick water from the pool unless the liner discretely reaches the surface behind them. Think about your options before deciding and consider installing a concrete collar to support slabs or timber to make the task easier.

Plants can be added immediately to a new pond but it’s best to leave fish stocking for a week or two to allow things to settle and ensure any unforeseen problems don’t arise. Add a water conditioner to detoxify chlorine, chloramine and heavy metals which might be in your tap water. Rainwater is a better choice for wildlife ponds, and you’ll often be surprised at how rapidly wildlife appears.

Fishponds will normally need filtration to remain clear and healthy, at the extreme end of things, koi require some significant life support equipment that will need planning for. Accessories such as bottom drains need to be installed during construction and are often the reason behind subsequent upgrades for dedicated enthusiasts. Space might also be needed for bulky filters, so be prepared to extend excavations to conceal these if needed.