How to build a garden pond: planning to maintenance

Water in your garden: more than decoration

There's something magical about water in a garden. It reflects light, attracts birds and dragonflies, and the sound of trickling water beats any playlist. But building a pond isn't a Sunday afternoon job. Good planning prevents green water, leaks and disappointment.

Tools like GardenWorld let you visualise how a pond would look in your garden. It helps you nail the position and proportions before you break ground.

Choosing the right spot

Pick a location that gets 5–6 hours of sun daily. Too much sun causes algae blooms; too little means water plants won't flower. Avoid spots directly under trees — falling leaves are the number one enemy of clear water.

Keep distance from boundaries too. A pond next to a fence can affect the neighbour's drainage, and a leak might send water under the fence. At least 2 metres clearance is sensible.

Depth guide

• Ornamental pond, no fish: 40–60 cm is plenty
• Goldfish pond: at least 80 cm
• Koi pond: at least 120 cm, ideally 150 cm
• Swimming pond: at least 200 cm in the deep section

A pond shallower than 80 cm can freeze solid in a harsh winter. RHS partner gardens and good aquatic centres will advise on the right depth for your plans.

Liner or preformed?

Liner (EPDM)

The most flexible option. You choose the shape and depth. EPDM liner (1 mm thick) is the industry standard — durable, flexible and UV-stable. Budget £7–13/m² for the liner plus protective underlay. Labour-intensive but the result looks natural.

Preformed shell

Easier to install: dig the right shape, drop in the shell, backfill with sand. Downside: limited shapes and depths. Suitable for small ornamental ponds up to about 1,000 litres.

Aquatic plants: your pond's engine

Plants aren't decoration — they're the biological filter. Without enough plants you'll get guaranteed pea-soup algae. Divide them by zone:

• Marginal zone (0–15 cm): Reedmace, Yellow flag iris, Water forget-me-not
• Shallow zone (15–40 cm): Water plantain, Arrowhead
• Deep zone (40+ cm): Water lily, Hornwort (oxygenator)
• Floating: Water soldier, Frogbit

Aim for 60–70% surface coverage. Sounds a lot, but it keeps the water cool and algae in check.

Equipment: pump and filter

A small ornamental pond with plenty of plants can run without a pump. But once you add fish or the pond exceeds 5,000 litres, a pump with filter is essential. Choose a pump that circulates the total volume at least once every two hours.

Do you need a UV lamp?

A UV-C unit kills suspended algae and keeps water clear. For a well-planted, fish-free pond it's not strictly necessary, but for fish ponds it's almost indispensable.

Year-round maintenance

• Spring: Restart pump, remove dead plant material, first water lily feed
• Summer: Remove blanketweed, check water level, feed fish
• Autumn: Net over the pond for leaves, clean pump
• Winter: Keep an area ice-free (floating de-icer), consider switching off the pump

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