How to build a raised pond
Raised ponds have many benefits. They don’t have to involve digging, they can prevent pets, children and wildlife from falling in and they can be built in a day, no problem. They look great too, and can really enhance a garden or patio. You can even disassemble and move house with them!
What materials do you need for a raised pond?
The easiest way to build a raised pond is with railway sleepers. New or old, railway sleepers are very strong, meaning that they will hold back the pressure of the water without bowing, while also providing a formal, architectural wall for your raised pond.
New railway sleepers typically come in set lengths like 6’ and 3’, so it's easy to create a 6’x6’ pond with them, without any cutting, or a 6’x3’. Get creative and you could use a combination of 6’and 3’ railway sleepers to create an L shaped pond. Other timber can be used for wooden ponds too, just make sure it's at least 2” thick to be strong enough to hold back the water without bending.
Brick or block built ponds are the ultimate raised garden ponds both in strength and for standing the test of time and are the best if building a large koi pond. Concrete blocks can be rendered on the outside or a rustic brick can make a newly built raised pond look instantly aged. Any bricklayer will be able to build you a raised brick or block pond.
The creative pond builder can use any rigid structure in combination with a pond liner, to hold water, and then clad the outside with a covering of their choice. At the small end tractor tyres can be used, half barrels or bathtubs. A Belfast sink can be turned into a raised pond, albeit a small one.
IBCs - commercial water holding vessels are purpose-built and used ones are widely available. Euro pallet-sized plastic containers originally designed for holding fruit can also make a great basis for a cheap raised pond. They are tough and safe for use as fish ponds. They just need disguising on the outside.
Getting started with raised garden ponds
The first thing to consider is placement. A raised pond should be near the house to take advantage of an outdoor socket and if you can, even enabling viewing through patio doors or a kitchen window when you are inside. Great for cold winter days. Place a raised pond at the bottom of the garden and you won’t be able to see the fish from the house, nor will you want to cross a muddy lawn to inspect it in autumn and winter.
Next is to make sure the site is level. Use a long length of timber and a spirit level to level up the area across its length, width and diagonal. The great thing about a raised timber pond is that you can build the first layer from four sleepers in a square shape, for example, fasten them together and then raise the frame in one corner to get it perfectly level.
Use shims made from thin slivers of timber to get the frame perfectly level at the base, and then every layer on top of that will be level too. This is especially important with raised formal ponds as if the frame isn’t level, the water always will be, so there will be differing amounts of liner and frame exposed at one end to the other and it won’t look right.
Rocks and roots puncture pond liners
Unless your proposed pond will have a solid concrete base, you’ll also need to prepare the base of the pond for pond liner just as you would for a standard in-ground pond. Clear the base of tree roots, sharp objects, rocks and stones and anything that could pierce the liner. Use underlay on the base and sides just as you would with other garden ponds.
Fastening railway sleepers together
The taller you build your raised pond, the more outward pressure the water will place on the perimeter. Sleepers should be fastened together with 90-degree angle brackets or if you’re handy with timber, coach bolts.
If you’re not using thick sleepers you could use vertical timber stakes or wooden fence posts in each of the four corners and then clad the timber frame around those, screwing the frame to the posts like you would with a raised vegetable bed. They’re built in exactly the same way. Make sure that no screw or nail tips are exposed which will puncture the liner.
How to line a raised pond
Calculate the pond liner size by measuring the depth, doubling it, and adding that number on to the length and width of the pond. So if the pond is 6’long by 6’ wide by 2’ high, double the depth to 4’ then add that to the 6’ in each direction. Give yourself a bit of an overhang at the top and you’ll need a liner which is about 12’x12’, or 4 metres by 4 metres in metric, and underlay to match. If you’re not sure about calculating your pond liner, there’s a ready-made liner calculator here.
Place the underlay in first, then using two people to carry the liner like you would a bedsheet, stretch it flat before loosely, and carefully draping it over the frame. Place a hosepipe in the pond as it starts to fill with water, apply gentle pressure to each side of the liner to stretch it out and enable neat folds in the corners. Fill to the top.
Capping for raised ponds
The great thing about raised ponds is how easy it is to hide and disguise the liner at the top. With your pond filled the spare liner will be draped around the outside edges. Take another layer of sleepers to create one final frame on top of the liner, fit, then trim the liner on the outsides of the pond.
If using any other timber frame, timber capping is available from timber merchants or DIY stores, and for brick, another layer of brick, small flags or concrete capping can be used. Fit the final capping layer then trim the exposed liner on the outside of the pond for a neat, professional-looking job.
Raised pond filtration
If you want to add fish to your raised pond you’ll need some form of filtration. A pump, filter and Ultra Violet Clarifier will keep the water clear of debris, break down fish waste and clear green water, but you want a discrete filtration solution at the same time which won’t spoil your vista.
For small ponds of 1000 litres or less, an all-in-one pump, filter and UV is the neatest solution where everything is built into the pump unit and is placed in the middle of the pond. These compact filters will provide a decorative fountain or run water features too.
For larger raised ponds the best solution is a pressurised filter with built-in UV. Unlike gravity-fed filters and black box filters, pressurised filters can be placed beneath the pond surface, behind the pond, or some distance away. They can even be buried up to their lids in soil. Place a solids handling filter pump in the middle of the raised pond, run hose to the filter, and then from the filter back to the pond. Many pressurised filters can also run dirty water to waste or a flowerbed when being cleaned.