Monty’s pond-making tips
Mark out the pond using string and canes, or a hosepipe. Allow for marginal plants by including shallow shelves around the edge, making these at least 45cm wide and as level as you can. Aquatic plants such as waterlilies need deeper water, so aim to include a section that is at least 90cm deep. Even digging a small hole will give you several barrowloads of soil, so plan what you will do with it – ideally incorporating it elsewhere in the garden.
Check the edges are all level. Use a spirit level and be exact, because water will instantly expose any inaccuracy. If the site is sloping, then you will have to build up one side. Avoid steep slopes falling down into or away from the edge of the pond.
Remove any stones or roots once you are satisfied with the shape and size, then firm and smooth the soil. If you are using a rigid liner, this can be fitted into the hole and the soil backfilled around the edges. If using a flexible liner, first cover the surface of the soil with a geotextile underlay, sand or carpeting underfelt. Whatever you use, the purpose is the same – to protect the lining from being punctured.
Calculate the size of the liner needed by measuring the longest distances along the length and breadth of the pond and then add three times the maximum depth to both measurements. A pond measuring 300cm x 180cm at its widest points, and 90cm at its deepest, will need a liner at least 6m x 5m – online sellers usually have calculators to help you work it out. Invest in a thick butyl liner – they are expensive but they stretch and are tough, so last a long time. Replacing a cheap liner is an expensive and messy business.
Open out the liner and leave it in the sunshine for an hour. This will soften it up and make it easier to fit. Stretch it gently over the pool and let it ease itself into all the contours, gathering folds where possible to avoid creases. Do not start to fill it until you are happy that it has as few wrinkles as possible. Weight down the excess liner around the edges with bricks or stones.
Fill with water, ideally using stored rainwater, pulling any creases free. The water will stretch the liner as it fills, ensuring a tight fit.
Trim the liner, leaving at least 60cm extra all the way round. Then add stones, soil and plants around the edges to hide the liner and create a natural-looking pond.
Monty reveals what anyone starting out in gardening needs to know
Longmeadow’s first pond, dug in winter 2012, has ledges at different depths to suit various marginal plants