Planning a garden pond

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Last updated 28th March 2015

Decisions to make when planning a pond
Siting the pond for the best effect
Planning the size and shape of your pond
A sunken or raised pond?
A bog garden alongside your pond?
Pond depth and profile
Liners for garden ponds – clay or sheets or pre-formed shells?
An electricity supply for a pond
Plants for a pond and bog garden
Fish decisions for a pond

Decisions to make when planning a pond

Your first decision is what you want from your pool – wildlife, a place for decorative fish, the sound of running water, the reflective surface of a sheet of water, the means of growing aquatic plants…or perhaps a combination of these.

For a pond to be proud of, take time to find out what’s needed by the plants and any fish you hanker after. Then you’ll be rewarded with a glorious display during the summer months. There’s even pleasure to be had in winter, with reflections in the water and the antics of birds as they descend to bathe or drink.

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Siting the pond for the best effect

Think of the visual impact that you can create with a pond – don’t hide it away. A pond should be the focal point of your garden, giving you and your visitors great pleasure all year round. You can draw the eye with statuary, a fountain or strategically placed boulders too, and combine the pond with a rockery to one side to add some height to the scene. Seating near the pool is also a good idea so you can enjoy the view in comfort. As you’re less likely to linger in the garden in the winter, it’s preferable to have a good view of the pond from the house too. And try to site your pond (and any adjoining rockery) so that it blends in with its surroundings, rather than sticking out like a sore thumb.

Sloping gardens pose more problems than flat ones. A pond looks far more natural at the foot of a slope. But if the ground slopes away from your house, then site the pond at the top of the bank, so that you can see the water.

Aquatic plants need good light for at least part of each day, so study your garden on a sunny summer’s day to decide on the ideal spot. Avoid parts of the garden overhung by tree branches, because, apart from the problems of shade, the roots will be as far out from the trunk as the branches. Digging through roots is not to be recommended because it can be hard work and will damage the tree. Additionally, future root growth could easily damage the liner and cause a leak. Leaves falling into the water are also a nuisance because the rotting process uses up the oxygen that the fish need to survive. Loads of leaves can be a nuisance in a fish-free pool too, as they will rot down to a sludge that will be difficult to clear if you ever have to re-line the pond. Don’t despair if the only suitable site for your pond turns out to be behind the garden shed. Link it to the rest of the garden with an attractive path. Or move the shed….

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Planning the size and shape of your pond

The size of pond is only limited by the size of your garden and your budget, but do go for the largest one you can. This is because the temperature of large bodies of water doesn’t fluctuate as much as smaller volumes. Swings in temperature affect fish badly and sudden warming encourages green algal growth too. As a rough guide, aim for a minimum of 4 square metres (40 sq.ft.) surface area, i.e. 1.3m (4ft. 3in.) diameter circle or 2m (6ft. 6in.) square.

Don’t rule out a smaller pond though, but be prepared to give it plenty of loving care and attention. You’ll certainly need to install a pump and filter to keep the water clear. Garden designers talk about formal and informal shapes, but what do they mean? Well, formal shapes are those you drew in geometry class at school (squares, rectangles, circles and ovals) and look good as raised or sunken ponds. Informal ponds have irregular and more natural outlines, and are easier to create as sunken rather than raised ponds. Formal and informal ponds look good in a formal garden layout, but a formal pond in an informal garden does look odd.

Once you’ve decided on a site, size and shape, mark out the pond’s outline with a hosepipe or canes, then give yourself a week or so to ponder before beginning. Move the outline around if necessary and only start digging (or building) once you’re completely satisfied that you’ve got it all right.

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A sunken or raised pond?

A sunken pond relies on the surrounding soil to support its sides, but a raised pond must have a support of some kind, usually of timber, brick or stone. It’s best to choose materials that blend in with those already used in your house and garden.

Both types of pond require a lot of work, but once you’ve dug out a hole for a sunken pond, you end up with a huge heap of soil which can present a disposal problem, unless you are planning a rockery. Handy for a waterfall that can look natural if you position the rocks and plants carefully.

Or course, whether you have a sunken or raised pond, you will need to stop the water leaking out. The most practical options are a tough but flexible pond liner (eg from Bradshaws or Pondkeeper) or a pre-formed shape (eg from Bradshaws or Pondkeeper). Both should be finished off with some sort of edging to protect the material from sunlight and hide it from view. It’s easy to incorporate a seat into the edge of a raised pond by using broad flat coping stones or timber decking. You can finish the edge in the same way for a sunken pond, and there’s also the option of taking turf to the water’s edge, although you will need to prevent mowings from dropping into the pond. Otherwise they will add unwanted nutrients to the water and encourage blanket weed.

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A bog garden alongside your pond?

Bog gardens can be created at the edge of pool by extending a flexible liner(eg from Bradshaws or Pondkeeper) over a lip so that soil cannot be washed into the water. Or safer still, create a bog garden with its own separate liner, which need not be an expensive pond version, but any thick plastic, as it will not be exposed to damaging daylight.

All you need is a shallow excavation (just deep enough to plant into) that you line with a sheet liner to prevent water draining away. Then backfill with garden soil and plant with marginals (ie plants that prefer the water’s edge – see Plants for a pond and bog garden) or plants which tolerate wet soil (eg dogwoods, dwarf willowprimulas, hostas, elephant’s ears (Bergenia), hostas, purple loosestrife (Lythrum), water avens (Geum rivale)). Don’t worry if you puncture a bog garden liner either, it will still retain most moisture. In fact we had to puncture our as, after some very wet weather, it was becoming more of a slurry than a bog, and the soil was being washed into our adjoining pond.

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Pond depth and profile

The pond should have a deep section, at least 45cm (18in.) deep (preferably 60cms (2ft) deep in colder areas) to give fish a good chance of surviving the winter. With this depth, even if the water freezes over on top, it should remain liquid in the depths.

The pond’s sides should be carefully shaped to avoid a saucer-like cross-section. The problem with a saucer shape is that much of the water is very shallow. Steeper sides result in a greater volume of water in relation to the pond’s surface area, which reduces the likelihood of temperature fluctuations. Vertical sides to a pond are possible for a raised design, but more difficult for a sunken type, because the soil tends to collapse as you dig. Aim for as steep a sloping side as possible in this case, incorporating a planting shelf part-way down for marginal plants.

Make one portion of the edge more gently sloping than the rest so that creatures can enter and leave the pond easily. After all, it’s quite common for hedgehogs to fall into ponds and drown because they can’t scramble back out; frogs and toads find steep sides a struggle too.

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Liners for garden ponds – clay or sheets or pre-formed shells?

Not many people create clay-lined ponds these days (with good reason…) but if you’re considering it, read our puddled clay article. For the range of sheet and shell liners, visit a water gardening centre or flick through a catalogue to see the range available. There are many pre-formed shapes made but it is easy to misjudge their size. Arm yourself with measurements before buying, otherwise you’ll come home with something far too small.

Pre-formed shapes work out more expensive than sheet liners, which are made of a flexible, slightly stretchy material, so the weight of the water moulds it to the sides of the hole. These liners aren’t so stretchy that you can skimp on the amount you buy though. You must have enough material to drape over the sides, base and edge of the hole. The length of guarantee is a good indicator of quality – don’t be tempted to use ordinary polythene or PVC sheeting because it is not made for this job and will fail within a few years.

Price varies according to the grade of liner, but the cheaper ones are more susceptible to damage by sunlight and puncturing. Stones in the soil puncture liners, as do tree roots and some grass roots, such as couch. The more the liner is stretched, the more susceptible it is to puncturing. A protective layer between the liner and the soil is essential. Sand plus a layer of old carpet, cardboard or newspaper are adequate to cushion a pre-formed liner, but a purpose-made underlay sheet is easier to handle and offers better protection for a sheet liner.

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An electricity supply for a pond

For a fountain, waterfall or other moving water (for its ornamental effect or aeration for fish or both) and for filtering out fish waste, you will need a pump, which in turn will need a mains electricity supply. This means an outdoor connector (e.g. from Pondkeeper or Screwfix) and possibly the advice of an electrician, although specialist water garden centres are very helpful. If you prefer to hide the cable, then plan to ‘lose’ it beneath the edging or behind the surrounds of a raised pond.

You can make good use of this supply in the winter for running a pond heater. This is essential to keep some of the surface ice-free for wildlife to access water, and to prevent toxic gases being trapped and killing any fish.

For very little work, you’ll have a beautifully lush display to complement your pond.

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Plants for a pond and bog garden

Avoid overwhelming the pool with over-vigorous plants – check their ultimate height and spread so you don’t have a jungle obscuring the view. And be careful when choosing water lilies, which range from miniatures to thugs that should only be planted in lakes.

There’s usually a good choice of plants at aquatic garden centres and specialist nurseries but you may need to use mail order for specific wants. For a basic range, there is Pondkeeper, and for a greater choice, see Unwins, who also have a wide range of pond plants. For even more marginals and aquatics, including waterlilies, see Bennett’s Water Garden nursery.

Do remember that pond plants are often grown under cover so you’ll need to harden them off (ie get them used to cold winds and cool night temperatures) gradually before you plant them out. The best planting time is mid-summer to give the plants time to establish before their first winter.

A few plant suggestions

Floating plants:
No need to plant these – just throw them in. But avoid duckweed (Lemna spp) which rapidly covers the pool’s surface and is difficult to eradicate once in the pond. Unfortunately it is often caught up in plants you buy to put in the pond, or spread from other ponds to yours by birds. Scoop it out as soon as you see it.

  • Frogbit (Hydrocharis morsus-ranae): Like a tiny water lily with white flowers, hardy (sinks to pool bottom in winter).
  • Fairy moss (Azolla caroliniana): A fern-like plant, quite hardy, turning reddish in winter, but will not survive severe cold.
  • Water soldier (Stratiotes aloides): Pineapple-type floating leaves, white flower, hardy, prolific. Provides shelter for insects.

Submerged oxygenators:
Mostly out of sight, but vital for pond health, taking up excess nutrients and shading the water from sunlight, so reducing blanket weed and green water. They also provide plenty of cover for amphibians, fish and insect life. See Unwins for their selection.

  • Hornwort (Ceratophyllum demersum)
  • Canadian pondweed (Elodea canadensis): Can be too successful, so be warned.
  • Elodea crispa
  • Autumnal starwort (Callitriche autumnalis): the best of the starworts and good for a wildlife pool.

Water lilies (Nymphaea):
These like still water so don’t place them near fountains. Check the planting depth required and their eventual spread. Beware of tender varieties that will not survive our winters, so have to be brought inside before it gets cold.

Other deep-water aquatic plants:
These need at least 30cm (12in) of water above their roots.

  • Water fringe (Nymphoides peltata): Floating leaves similar to water lily, yellow fringed flowers and very hardy.
  • Water hawthorn (Aponogeton distachyos): Floating leaves, white flowers spring to autumn, hardy.
  • Water crowfoot (Ranunculus aquatilis): Small white flowers in spring, floating leaves are clover-shaped and submerged leaves are ferny. Happy in moving water.

Plants to place in pots on a submerged shelf or plant at the water’s edge:

  • Water plantain (Alisma platago-aquatica): Upright leaves and flower spikes. Seeds provide food for wildlife.
  • Water forget-me-not (Myosotis palustris or scorpioides)
  • Bog arum (Calla palustris)
  • Flowering rush (Butomos umbellatus)
  • Sedge (Carex/Cyperus/Scirpus): Semi-evergreen types provide winter cover for wildlife.
  • Bog bean (Menyanthes trifoliata): Flowers are good for insects.
  • Cotton grass (Eriophorum angustifolium)
  • Water irises (Iris laevigata)
  • Yellow flag iris (Iris pseudoacorus): Invasive. Flowers attract insects; seed provide food for wildlife.
  • Variegated manna grass (Glyceria maxima ‘Variegata’)
  • Corkscrew rush (Juncus effusus ‘Spiralis’
  • Water mint (Mentha aquatica): Can be invasive. Flowers are good for insects.
  • Pickerel weed (Pontaderia cordata)
  • Marsh marigold (Caltha palustris): Attractive to insects.
  • Houttuynia (Houttuynia cordata)
  • Dwarf reedmace (Typha minima): Often referred to incorrectly as bulrush, reedmace has a brown poker-like flowerhead. Can be invasive.
  • Brooklime (Veronica beccabunga): semi-evergreen, grows on water and boggy soil, tiny blue flowers.
  • Arrowhead (Sagittaria sagittifolia)

Bog plants:
Many of those marginals listed above will thrive in a bog garden. Additionally, there are numerous other wet soil lovers including these:

  • Day lily (Hemerocallis): range of colours.
  • Meadowsweet (Filipendula ulmaria)
  • Creeping Jenny (Lysimachia nummularia): For soil at the pond’s edge, so the trailing growth can hide the pond edge. Can be invasive. Bright yellow spring/early summer flowers.
  • Astilbe (Astilbe)
  • Goat’s beard (Aruncus dioicus)
  • Japanse iris (Iris ensata)
  • Siberian iris (Iris sibirica)
  • Monkey flower (Mimulus)
  • Drumstick primula (Primula denticulata)
  • Candelabra primula (Primula spp)
  • Globe flower (Trollius)

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Fish decisions for a pond

Make sure that fish will thrive in your pond by only stocking fish that will like the conditions it provides. Also provide plenty of hiding places for the brightly coloured varieties that draw the unwelcome attention of herons. Plenty of pond plants, along with a piece of clay pipe on the pond bottom will give them some cover.

Choice of native fish

Trout – these require more oxygen than other fish, so are not very practical for small ponds or where there’s no power supply to drive a waterfall or fountain. Trout must be introduced at the same time as other fish. If not, the trout will eat the newcomers.

Tench and golden tench – these are scavengers that keep the pond clean.

Golden rudd – add colour and movement to the pond.

Roach – these like still waters and reeds.

3-spined stickleback – familiar little fish from childhood pond-dabbling days.

Choice of introduced fish

Orfe – these come up to the surface and jump up to catch insects.

Goldfish – undemanding colourful creatures.

Koi carp – available in a range of sizes and colours. If you’re serious about Koi and growing prize specimens, you’ll need to build a purpose-made specialist pond extra deep and kitted out with lots of 
equipment. See:
Water purifiers for Koi ponds
Vacuums for cleaning fish ponds
Surface skimmers for fish ponds
Venturis for aerating fish ponds
Air pumps for fish ponds
Ultraviolet (UV) light to control green pond water
Filters to clean pond water

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