EVEN BEFORE we’d finished filling it, a frog had found its way into our new pond, plump-looking, so presumably a female ready to spawn. We had disturbed her as we went hunting for stones to cover the PVC liner around edges. I’ve been putting off the task of reinstating our garden pond for months but once we’d got our materials together and allowed ourselves enough time for the job, it was a reasonably simple process.
The worst part, which we completed yesterday, was dismantling the old pond which had sprung a leak, caused by damage to the liner I suspect. I thought that I’d have some pondweeds to rescue but after six months all that remained in the sump of the pond was smelly black silt and debris which I spread on the garden. I was pleased to find that there were no rodent burrows beneath the liner, a problem which led our neighbours to replace their leaky liner with a fibre glass pond, a more expensive option and more difficult to install.
Pond Liner
At the garden centre we found a Blagdon 0.5mm PVC small pond liner, 3.5 x 4m, precisely the size that I’d calculated that we would need, in a pack that included synthetic underlay. It comes with a lifetime guarantee.
The way to calculate how much liner you’ll need is:
Length plus twice the maximum depth x width plus twice the maximum depth
We asked for advice on covering the edges and the man at the aquatic centre drew us this diagram to suggest a shallow shelf around the edges with stones resting on the liner, half in and half out of the water. The edge of the liner folds up behind the stones and you trim off the surplus when the pond is full. This has the advantage that the upstanding edge of the liner prevents water wicking away to the surrounding soil.
We already had the level of the previous pond to work from, but as I cut the 6 inch by 1 inch deep shelf along the far edge of our pond, I kept checking it with a straight edge and a spirit level.
How to Construct a Pond
With apologies for the illustrations – I’m still experimenting with filters in Photoshop!
1. Remove all stones and roots from the hole, trample around to make the ground as smooth as possible then (and this is optional) spread a layer of sand around the hole. Our pond is an inch or two more than 3 metres x 2 metres (10ft x 6ft 6in) with a maximum depth of 45cm (18 inches). That’s sufficient for a wildlife pond but a pond for fish should be 6 inches deeper. It slopes very gradually from the left to allow access for birds and animals. On the other three sides there’s a ledge about 20 cm (8 inches) deep for pots of water plants. 
2. Spread a fleece liner across the hole. This is simpler, though more expensive, than the layer of damp newspaper that we used for our first pond, along with an old carpet. Barbara pressed the wet newspapers into place with her bare feet. I guess it’s a sort of therapy. But the soft synthetic fleece is better because it never rots and it adapts easily to the shape of the hole.
3. Next comes the pond liner. Make a couple of large tucks or folds (a dressmaker would call them darts) to allow the liner to adapt to the contours but you don’t need to precisely fit the liner into the hole as the weight of the water to do that. Place a large stone, one without sharp edges, at each corner to prevent the liner flapping about in the breeze.
At this stage it’s hard to believe that this will ever become a natural-looking pond.
4. Fill the pond
5. As the pond fills add rocks around the edge.
6. Cut off the corners and any surplus liner around the edges and cover the edges with flat stones and turf.
At the left-hand edge where we had used some mossy rocks, the pond looked as if it had been there for years. We’re going to leave it for a few days before adding pondweeds, to allow the chlorine in the tap water to dissipate.
Links; Thanks to the Nautilus Aquatic Centre for the helpful advice.
Blagdon the Pond Masters