I inherited a small pond when I bought my house and while I like the idea, it's been a source of irritation.
Cast in concrete in the 1960s, it has straight sides - so wildlife can't get out and it's not deep enough to grow the plants I want.
As the liner developed a leak last summer, I decided to fix some of the faults.
Autumn and winter's the best time to do it, but beware - it's a cold, smelly and wet job.
If you're building a pond from scratch, dig a hole with slanting sides and planting shelves for marginals.
It needs to be about 60cm (2ft) deep for plants and fish, otherwise it will freeze in winter and evaporate in warm weather.
For your pond underlay and liner, use this formula: measure the length, width and maximum depth of your pond. Twice depth plus width; twice depth plus length = the minimum size to buy.
In practice, liner and underlay often comes in packs (my underlay was 2m x 8m when I only needed 2m x 3m). If you're relining a pond, here's what to do:
1) Drain the pond and keep any plants in buckets of old pond water. Once you get to the mud at the bottom, an old stiff whitewashing brush is handy to remove gravel and silt. ALL stones must be removed before new underlay/liner goes in, as you'll void any guarantee.
2) Make alterations to the size. I filled in a totally pointless 'arm' and in doing so, made it slope gently so creatures can climb back out. Pack this down securely.
3) Next, the underlay (have someone help you with this). I doubled mine up as there was so much left over. Make sure it roughly fits and hold the edges down with rocks.
4) Finally, the liner. With your helper, position it so it's in about the right place but DON'T stand in the pond, as you could puncture it. I found a soft brush was useful in pushing the liner into awkward corners. Don't worry if it's all over the place - you can adapt it as you fill it. Hold excess liner down with bricks.
5) It's best to let ponds fill naturally with rainwater, but unless you want your garden to look like a building site, use a hose with tap water. While the water's running in, pull and fold the liner so you get a neater finish. Fill to the top and make sure it's level.
6) Leave for 24-48 hours to settle.
7) Finishing off: cut away excess liner and underlay, leaving about 30cm (1ft) of spare. You need to hide the liner with an edging of your choice overlapping the water. The nutrients from the tap water will mean too much algal growth and it will go like pea soup, but a bale of barley straw will sort it out.
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