Sophie Barnes
Why a pond earns its place on the plot
If you only make one wildlife feature this year, make it a pond. Nothing else comes close for the sheer number of creatures it pulls in. A frog will hoover up slugs, snails and beetles all summer, a toad will patrol your brassicas at dusk, and newts will quietly mop up slug eggs and small larvae. Dragonfly and damselfly nymphs are voracious predators of midges and mosquito larvae, and the adults will hunt aphids and flies over your beds.
There is a quieter benefit, too. A pond gives you somewhere to sit at the end of a digging session, watching swallows dip for a drink and bees land on the marsh marigold. On an allotment, where every square metre usually has to justify itself, that counts for something.
Choosing the spot and the size
You do not need a big garden, and you certainly do not need a big pond. Something around 1.5 metres by 1 metre, with a deep section of about 60cm, will support frogs, newts and insects happily. If space is tight, a half barrel or a sunken washing-up bowl will still bring in damselflies and give birds a place to drink.
When you are picking the site, think about these things:
- Sun and shade. Aim for part sun, part shade. Full sun all day encourages blanketweed; deep shade keeps the water cold and plants sulk.
- Trees and hedges. Keep well clear. Leaves foul the water, and roots will eventually find a liner.
- Level ground. A pond on a slope is a nightmare to edge neatly. Choose the flattest spot you have, or build up one side with soil and hide it with planting.
- Water source. Site it near a water butt if you can. Rainwater is far better for ponds than tap water.
- Visibility. Put it where you can see it from the kitchen window or your favourite bench. You will notice far more wildlife that way.
Digging and lining
Mark the shape out with a length of hose or a rope laid on the ground. Curvy, irregular edges look natural and give wildlife more places to shelter than a neat rectangle.
Dig in two stages. First, take out a shallow shelf around the whole perimeter, roughly 25cm wide and 25cm deep. This is where you will stand your planting baskets. Then dig the centre down to at least 60cm, which gives frogs somewhere to overwinter and stops the pond freezing solid in a hard frost. Check the rim is level by laying a straight plank across it with a spirit level on top — get this right now and the edging will be easy later.
Pick out sharp stones and any stubborn roots, then line the hole with old carpet, underlay or a proper geotextile. On top of that goes a butyl or EPDM liner. Allow at least 50cm of overhang all the way round; fold the corners into neat pleats rather than cutting them. Weight the edges down with turf, stone or paving while you fill.
Filling, planting and edging
Fill with rainwater from a butt. If you must use tap water, let it stand for a couple of days first, and accept that a brand-new tap-filled pond often goes green for a few weeks — it settles.
Plant generously but choose natives where you can, and always use loam-based compost rather than rich multipurpose, which leaks nutrients and feeds algae.
- Oxygenators: hornwort, water starwort or spiked water milfoil, roughly one bunch per square metre.
- Marginals: marsh marigold, water forget-me-not, brooklime, lesser spearwort and flowering rush for the shelves.
- To avoid: floating pennywort, parrot's feather and New Zealand pigmyweed. These are invasive and must not be planted.
Skip fish entirely. They eat tadpoles, dragonfly nymphs and just about everything else you are trying to attract. Finish the edges with a gently sloping beach of stones or a log laid into the water — frogs, hedgehogs and thirsty birds all need a way in and out. Leave a patch of long grass and a small log pile nearby and you have a proper habitat, not just a pond.
Looking after it through the year
Expect a flush of green algae in the first spring. This is normal, and it passes as your plants establish and shade the water. Never reach for chemicals. A handful of barley straw in a net bag can help, and patience helps more.
Keep the water topped up with rainwater through summer, and rake out excess blanketweed with a stick rather than your hands. Net the surface in autumn if leaves are a problem, but don't tidy too ruthlessly — a little leaf litter is food for something.
If the pond silts up badly, clean it out in late September, every three to five years. Empty the silt onto the edge and leave it there for a day or two so that any trapped newts, snails and larvae can crawl back in. Never clean a pond out in spring, when frogspawn and tadpoles are in the water. In winter, do not smash the ice — the shock can kill hibernating frogs. Float a ball or rest a pan of hot water on the surface to melt a hole instead.
Keeping it safe in a family garden
If you have toddlers, either fence the pond, fit a sturdy metal grille just below the surface, or build a raised one with a wide, solid rim. A raised pond is also kinder to your back and easier to enjoy from a chair. Once children are older, use the pond as a teaching tool — pond-dipping with a white tray and a magnifying glass is one of the great pleasures of a garden, and it costs almost nothing.
Build it once, plant it well, and leave it largely alone. The frogs, newts and dragonflies will do the rest, and your cabbages will thank you for it.
