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How to dig a large pond
- Activity time:
- More than 2 hours
- Difficulty level:
- Suitable for:
- Large garden, Medium garden
- To help:
- Frogs, toads & newts, Dragonflies & damselflies, Bats, Birds, Pond creatures
There's something enchanting about sitting next to a large garden pond, and it's amazing how quickly wildlife will find it.
Yes they are a challenge to make, and aren't cheap, but they will repay you massively.
In summer, it should be only a short matter of weeks before pond skaters and water beetles arrive under cover of darkness. You might get dragonflies and damselflies in your first season. And frogs and newts are likely within a year.
Don't be put off by flushes of algae, which are either stringy or turn the water green or brown – that's normal in a new pond.
You can build a pond at any time of year. But in autumn, the ground isn't too wet or dry, so it's ideal for digging.
What you will need
- Large, quality pond liner
- Pond underlay
- Builders' sand
- Spade or even mini-digger
- Spirit level
- Pond plants – marginals and submerged
- Aquatic baskets
- Optional: washed gravel
- Choose your location. Have you got room in your garden for a large pond? By large pond, we mean one which is 2m x 2m in area and sometimes much more. If you do, it’s one of the most rewarding things you can do for wildlife.
Choose a spot with plenty of sunshine and that doesn't present any flood risk - think where excess water will go if it overflows.
Ponds often look best in the places they would form naturally – the lowest point in the garden – but it isn't essential.You are likely to create quite a lot of spoil as you dig, so decide where that is going to go. You could create raised beds and earth mounds as another wildlife-friendly feature elsewhere in the garden.
- Think safety: if you have young children, or you have young visitors, the pond will need to be somewhere they can only get to if supervised.
- Design the shape of your pond. The golden rules for large ponds are:
Shallow shelving margins - make sure that anything such as hedgehogs that fall in can easily get out
Deeper areas, but you don't need to go too deep (600mm in the middle is fine)
Plenty of submerged aquatic pondweed
Plenty of emergent vegetation.
You can get creative with your shape, using wiggly margins or a perfectly geometric shape - wildlife won't mind either way. Try doing a sketch on paper, however rough - it can really help.
- Choose and buy your pond liner
Although it’s possible to line a pond with concrete, we recommend either a pre-moulded liner. Usually fibreglass, they are expensive but durable. A flexible liner. Materials include plastic (PVC), butyl rubber and EPDM rubber (such as Firestone).
They’re the easiest way to create a pond to the dimensions you want, but are easily punctured so lay and look after them with care. Remember, flexible liners don't bend round right angles so use them for more naturally curving ponds. You’ll be really disappointed if your pond leaks, so spend wisely, not cheaply.
A flexible liner will come as a large rectangle. The liner dimensions you will need will (the maximum length of the pond plus twice the maximum depth) by (the maximum width plus twice the maximum depth).
So a 2m x 2m pond which is 500mm deep in the middle will need a liner 3m x 3m. As a rough price guide, a liner for a pond that size will cost around £50 - a 10m x 10m liner will cost more than £600. Buy an equivalent amount of proper pond underlay - it is much cheaper than the liner.
- Dig your hole. Mark out where your pond is with lengths of hosepipe laid on the ground or lines of builders' sand work well. If you are using a ready-made liner, create a template in cardboard of its outline. Stand back and look at it from every angle, including from inside your home – does it look good?
For really big ponds, you may want to hire someone with a mini-digger to take some of the strain. Create horizontal shelves where you will be able to put aquatic plants in pots. It’s really important to carefully check levels from each side of the hole to the other with a spirit level - every part of the pond margin should be at the same level.
- Line your hole.
If you are using a ready-made moulded liner, lower it into the hole to test that you have dug the correct shape. Dig a little bit more earth out than the size of the liner so that it has a bit of wriggle room. Then pack the base with a protective layer of sand, lower the liner into position and carefully pack sand around the sides.
If using a flexible liner, dig a slightly larger hole than you need (about 50mm extra all the way round and down). Then make sure you remove all rocks, roots and sharp objects from the hole.
- Protect the liner. To ensure the liner doesn't get punctured once it's weighed down with a 50mm layer of sand all around the hole. Then over this lay sheets of man-made pond underlay – it’s like a fleece that rocks and roots can't penetrate.
Now you can unfold your liner across the hole. Remember that EDPM and rubber liners are very heavy, so you may need some help. Push it loosely into the contours. Take great care not to snag the liner – maybe take your shoes and socks off!
If you want to, put some washed gravel into the base – it provides cover, and it protects the liner. But if you want to use soil, only ever use the special aquatic compost, devoid of almost all nutrients – garden soil will give you algae problems forever.
- Fill with water. It’s best to use rainwater, as tap water contains nitrates and phosphates which may give you algae problems. It doesn't matter if it takes a few weeks to fill. Leave the pond for a week or so to settle.
- Edging the pond. So now you have a pond full of water but with bits of bare liner all around the outside. Most people like to hide this, but it is one of the trickiest jobs in making a large pond. Many people use large rocks or slabs, often concreted into place. Some people lay turf over the edge, but you need a thick layer of soil, some of which may wash nutrients into the pond, and the grass roots will suck up water from the pond, increasing the rate at which the water level drops in dry weather.
- Buy some aquatic plants - but choose very carefully. You want a range of plants which look attractive and perform different functions to keep your pond healthy. Choose ones which won't grow too large for your pond, and above all avoid any invasive non-native species. Only buy from a reputable company.
Submerged pondweeds are useful as places for pond creatures to hide and lay their eggs. Choose rigid hornwort, whorled water-milfoil and starwort.
Floating aquatics like pondweeds (look for those called Potamogeton), fringed water-lily Nymphoides peltata (which is smaller and less likely to overrun the pond than most other waterlilies, but NOT in Ireland, where it's non-native) and water soldier provide a useful surface cover and shade for the wildlife under the water. They can be placed in deeper water too.
Emergent and marginal plants like marsh marigold, water plantain and flowering rush can be planted around the edge to provide cover for resting and nesting wildlife.
- Planting up. Your aquatic plant pots (they look like they are made from mesh) are likely to come ready to be put straight in your pond. When you need to move your plant into a bigger pot in a couple of years' time, use special aquatic compost which is low in nutrients.
Spread a layer of small gravel around the top of the pot to stop the compost being washed into the water.
- Aftercare. For the first few months, don’t worry if you get algae or blanket weed (it’s like strings of green gloop). Get children to remove it by winding it around a stick – it’s fun!
It's normal in a new pond and as your pond matures, all the pond creatures you’ve attracted will help keep the water clear.
You may need to top the pond up in hot weather – try to use rainwater from a water butt.
- And now watch wildlife arrive! Most of the creatures that use ponds are expert at finding new ones. Minibeasts like pond skaters and water beetles are surprisingly expert flyers are will arrive of their own accord during the summer months. So there's no need to bring in wildlife from other ponds, and especially don't bring amphibians (frogs, newts and toads) from elsewhere – you risk spreading the viruses they suffer from. Just keep peering in and you'll see wonderful things.