Ponds

Building and relining ponds

I inherited a small pond when I bought the house and while I like the idea, it’s been a source of irritation. Cast in concrete in the 1960s, it had straight sides so wildlife couldn’t get out and wasn’t deep enough to grow many plants.

When the liner developed a leak, 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, especially if you fall in like me.

Finished pond
February: newly relined

If you’re building a pond from scratch, dig your 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. Liner and underlay often comes in packs (my underlay was 2m x 8m when I only needed 2m x 3m).

Pond algae barley straw
April: algal bloom, being treated with barley straw

The practical stuff:

  • Drain the pond and keep any plants in buckets of 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.
  • 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.
  • Next, the underlay (have someone help you with this). I doubled mine up as there was so
    George
    George eating ribbon grass in the pond as fast as it grows

    much left over. Make sure it roughly fits and hold the edges down with rocks/bricks.

  • Finally, the liner. With your ‘willing’ 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 long-handled brush was useful to push 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.
  • If you live in an area of heavy rainfall and you don’t mind your garden looking like a building site, let nature fill it up. However, I live in a dry-ish part of the country, so tap water it had to be. 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.
  • Leave for 24-48 hours to settle.
  • Finishing off: cut away excess liner and underlay, leaving about 30cm (1ft) of spare. You need
    June: Rodgersia and edging plants
    June: Rodgersia and edging plants

    to hide the liner, as UV light can weaken some types. I used stones and fossils I’d collected with the kids from Seaham and Saltburn beaches. Have your edging overlapping the water so you can’t see the liner. I stuck the stones with Gorilla Superglue.

  • 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 eventually.
  • Replant saved plants in fresh aquatic compost in pond baskets and add new ones – I chose a pygmy water lily ( the only one that can survive in a shallow pond), plus rescued bits of variegated sedge and water iris.

Cleaning out a pond

The vilest job of the year is clearing out the pond. Some ponds are never cleaned and manage well, but mine suffers from leaf fall twice a year – in autumn, then from the beech hedge in spring.

Clearing out the pond
Handful of slime – clearing out the pond

General advice is to clean it out in autumn – I usually end up doing it in winter and late spring.

I used to have a purpose-built net for removing duckweed, tiny aquatic plants which float on the surface. However, you’ll find a sieve from a cheap shop does the job just as well, especially if you attach it to a cane. They cling around the water iris rhizomes, so if you can’t get the net in, blast it with a hose on the jet setting. When they’re in the main body of the pond, you can scoop them up.

Elodea, or waterweed,  is vital for oxygenating the water, but it runs rampant. Oxygenators are needed for the health of the water and to prevent algal growth (the green slimy stuff).

Don’t clear all the Elodea out – leave some in. Once you’ve cleared out what you don’t need, leave it in a pile by the side of the pond, so any wildlife can get back into the water.

With a sudden change in the natural balance of the pond, the water may turn green, especially in spring. If this happens, barley straw tied in a net bag and suspended in the pool will cure the problem (you can get it at garden centres).

If you want to plant new aquatics, spring’s the time to do so.


Tiny ponds to boost wildlife

Water iris and Californian poppy
Water iris and a rogue ‘perennial’ Californian poppy signal the start of summer

Even a small pond can make all the difference to the biodiversity of your garden.

Here’s one you can make with a tub – for a balcony or back yard. You’ll need a tub about 40cm deep (with no water holes, obviously). Fill it with water in situ, as it will be very heavy.

Use aquatic plants like Nymphaea pygmaea (pygmy water lily) and Callitriche verna (water starwort), planted in aquatic compost in baskets.

Always have safety in mind, so place secure fencing around it or metal caging on top if there are children around (or if the dog drinks out of it). Put logs and pebbles around the water’s edge to give easy access for wildlife.