Creating a pond

Before you get started, hear some quick tips for creating a garden pond from our Head of Organic Horticulture, Chris Collins.

Why make a pond in your organic garden? For three simple reasons:

  1. Within a short time it will attract birds, amphibians and insects - increasing the wildlife in your growing area.
  2. You can choose a variety of attractive plants, from marsh marigold to water mint, and Hollywood-style water lilies.
  3. But perhaps most importantly, you have a wonderful place to sit, observe, and enjoy the waterside wildlife.

See here for further advice on wildlife gardening,

Where?

  • Choose a site with plenty of sunshine. This helps the plants to grow and keeps the water warm.
  • Avoid trees. Their roots can disturb or pierce the liner, and autumn leaves can choke and clog the water.
  • Ponds should be safe. Young children can drown in 8cm of water.
  • It would help with maintenance if access is easy - you will be pulling out excess weed and tending your planting.

What?

Ponds can be any shape or size. You can buy a pre-formed shape, or dig and line your own design. See below for instructions.

When?

Autumn or early spring are probably the best time of year for pond installation. Avoid frost during construction (it makes the earth hard to dig), and delay any planting in your new autumn pond until Spring.

How?

First, mark out your site. If you are using a preformed pond, place it on site and mark its perimeter with a line of sand. If you are designing your own pond and using a liner, don't make the outline too ornate - it is hard to fit the liner into tight curves and angles.

A pond should be up to 60cm deep at one point. This allows wildlife to be safe during prolonged spells of hot or cold weather. However, it is the shallow water that most wildlife enjoys, such as tadpoles, damsel flies and baby frogs. And you might want ledges for planting under the water. Ideally plan for different depths.

Now dig the hole. Have a sheet of plastic or board nearby to put your soil and turfs on. Keep topsoil and the more stony subsoil separate. The latter is useful for building up levels under the liner, the former for planting round the pond edge.

For a preformed pond

  • dig approx 5 cms wider and deeper than the pond shape
  • back fill with 5 cms of sand and check levels with a spirit level on a piece of timber resting across the top.
  • now rest the pond on the sand, making sure it is firmly supported at all points
  • as you fill the pond make sure the edge stays level with the ground, backfilling with sand and subsoil if necessary
  • either create a border with discarded top soil, or use replaced turfs

For a lined pond

  • you need to create a shallow area somewhere around the perimeter to allow wildlife to get in and out easily. This isn't easy to do. If you create a slope, it often leaves an ugly expanse of pond liner as the water levels drop (which they will). Best advice is to first dig your whole pond area to approx 20-25 cms deep. (This will eventually be covered with subsoil, after you have filled the pond, hiding the exposed lining.) Then dig your deeper central hole, leaving a shelf at least 30 - 40 cms around it. By now you are in subsoil, which is paler and often stonier than the top soil. Keep this subsoil on a plastic sheet for use later.
  • in general, dig a further 10 - 15 cms deeper than you estimated - this allows for a bottom layer of sand or rubber underlay to protect the liner.
  • remove all sharp stones and other hard objects from the hole to protect the liner.
  • firm around the base and sides of the dug area. The soil must not cave in when you are placing the liner in position.
  • make sure the pond edges are level with each other in all directions. If necessary build up a side to achieve this. Check with a spirit level on a piece of timber.
  • before you lay the liner, put a layer of sand, then carpet or cardboard, or thick layers of newspaper. Or buy purpose-made underlay.

Lining the pond

  • to buy liner, use the following measurements: Length of pond + (maximum depth x 2); width of pond + (maximum depth x 2). Eg, for a pond measuring 1m x 40cm and 60cm deep: 100 + (60 x 2) x 40 + (60 x 2) = 240 x 160cm.
  • lay it over the hole. Make sure there is about 30-40cms overlap around the edges. Dip it half-way to two thirds into the hole, but don't try to shape it close to the sides.
  • weigh down the sides of the liner with heavy stones around the pond edge.
  • fill the pond with water. As the weight of the water increases, keep pulling and smoothing the lining so that it stretches and fits snugly against the sides. If you have to build up any areas, make sure the soil is compacted down hard. If you don’t, it’ll settle later, and drain some of the water away. You can use tap water, or fresh rain water from a butt.
  • now you can make the sloping sides. Place the subsoil on the shelves round the side, building it up to the edge. Leave some areas as a shelf, which is useful for putting plants onto.
  • the pond will look an unpromising muddy mess, but this will soon clear. After 3-4 days the water will reach air temperature, and some of the tapwater chemicals will evaporate.

Planting

  • Wait until Spring when frosts are over.
  • For one or two days after filling the pond the water will be crystal clear. It will then, almost overnight, become bright green, like pea soup. This green growth is algae, growing as a result of sunlight mixed with nutrients in the water. Don't worry, and don't replace the water. As the water creatures start to feed, and as the plants start to grow, the algae will be starved out.
  • Aim to have about 1/3 of the pond surface covered with a variety of plants. See the list below for deep water plants, emergent, marginal and floating plants
  • If you have a boggy area next to the pond then choose plants which enjoy moisture at their roots, such as Primula, Lysimachia, Astilbe.

Deep water plants

Water lilies (Nymphaea alba, Nymphaea lutea ) (Note - it is very important to choose the correct size of lily for your pond)

Water hawthorn (Aponogeton distachyus) - will tolerate 8-60 cm of water.

Broad leaved pond weed (Potamogeton natans)

Amphibious bistort (Polygonum amphibium)

Marginal plants

These plants grow in the shallows at the pool edge. Some (not listed) can become very invasive, so choose with care.

Flowering rush (Butomus umbellatus)

Marsh marigold (Caltha palustris)

Golden sedge (Carex stricta 'Bowles Golden')

Pendulous sedge (Carex pendula)

Yellow iris (Iris pseudocorus)

Lobelia (Lobelia fulgens and* L. cardinalis*)

Water mint (Mentha spicata)

Water plantain (Alisma plantago-aquatica)

Bog bean (Menyanthes trifoliata)

Arrowhead (Sagittaria saggitifolia)

Lesser reed mace (Typha minima) – Beware of Bulrush, T. latifolia, it is too large and invasive for garden ponds

Oxygenators

These submerged plants provide food and shelter for pond life. In addition they absorb minerals and carbon dioxide which helps starve algae and keeps the pond water clean:

Water milfoil (Myriophyllum spicatum)

Water buttercup (Ranunculus aquatilis)

Hornwort (Ceratophyllum demersum)

Water violet (Hottonia palustris)

Floating plants

Water soldier (Stratiotes aloides)

Bladderwort (Utricularia Spp)

Frogbit (Hydrocharis morsus-ranae)

Duckweed (Lemna spp) often comes with purchased plants. This tiny leaved plant can cover the surface in no time at all. The only way to get rid of it is daily removal until all traces have vanished.

Alien species

The following is a list of alien invasive species. These have been introduced into ponds as ornamentals. They are a threat to native plants when they escape and rapidly colonise waterways and ponds. Unfortunately, some garden centres and aquatic specialists are still selling these plants.

New Zealand pygmyweed - Crassula helmsii

Parrot’s feather - Myriophyllum aquaticum or M. proserpinacoides

Fairy moss or Water fern - Azolla caroliniana

Floating pennywort - Hydrocotyle ranunculoides

Pond Management

Once established, a pond is fairly self-managing. However, in the autumn, leaves should be removed as they can decompose and cause toxic conditions. A net spread over the surface will prevent them entering the water. As plants grow, they will need to be split and kept to a reasonable size for the pond. Work like this, causing major disturbance, is best done in late summer, after frogs, toads and other creatures have hatched, and before hibernation starts. Any major pond overhaul can take place at this time.

Long spells of hot weather can cause excessive evaporation in a small pond, which will need topping up. Water straight from the tap contains chlorine. Fill a can or two with water and allow to stand for 24 hours to allow the chemicals to evaporate, then add to the pond. A good system is to add the water to the pond in the evening, refill the containers immediately and allow to stand for 24 hours until the next evening.

Weeds can choke a small pond. To keep duckweed or blanket weed under control, remove excessive growth ruthlessly. When you pull them out, keep piles of weeds by the side of the pond side for a day. This allows pond creatures to crawl, or fall, back into the water.

The Freshwater Habitats Trust has advice on making freshwater ponds as well as information about aquatic wildlife