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 Constructing
a Garden Pond Using a Flexible Liner
It would probably be a good
idea to read Deciding
to Make a Garden Pond first, where you can read about
the different kinds and materials available.
Because a raised pond is
more a building than gardening project, I will only deal
with a sunken pond that is eventually intended to look like
a natural feature in the garden.
Decide where the pond should
go, ensuring it is not shaded or likely to get lots of leaves
dropped into it from surrounding trees.
Flexible Liners
You will also have to make a decision on the liner. Will
you buy a pre-formed fibreglass shell
or sheet lining which will adapt to any shape or size? If
a flexible liner is your choice, you have a choice of three
main types:
- Butyl rubber
- the most expensive type of lining but also the one that
is strongest and will last the longest time, perhaps 40
to 50 years. It isn't as liable to damage from ultraviolet
light (sunlight) nor the ravages caused by bacterial growth
or frost. Its strength means it is also less liable to
get torn or punctured.
- PVC
- this is less expensive than butyl rubber and many manufacturers
will give a guarantee of 10 years on it. It is relatively
strong and is not usually damaged by frost or bacterial
growth. It is susceptible to ultraviolet damage and eventually
exposed lining will become hard and crack. It will usually
last several years, though.
- Polythene
- not recommended for ponds but could be used for bog
gardens. Although it is the cheapest form of pond
lining, it is probably a false economy. It tears and punctures
much more easily than either of the other materials and
is much more susceptible to ultraviolet light.
Calculating the Liner
Needed
First level
the ground and mark out your pond with pegs and string,
a hosepipe or sand. This will give you the shape and size.
Now calculate how much liner you need. To do this, measure
the maximum width, length and depth. Now double the depth
and add it to the maximum width and to the maximum length.
Add an extra 6 to 9 inches for the overlap around the pond.
For example, the calculation for a pond that is 5ft wide,
10ft long and 3ft deep would be:
depth of 3ft x 2 = 6ft, width
of 5ft + 6ft = 11ft, length of 10ft + 6ft = 16ft plus the
6 to 9inches overlap.
Your pond liner would therefore need to be 11ft 6ins wide
and 16ft 6ins long.
Constructing Your
Pond
- Remembering to keep the
topsoil and subsoil separate - do not mix them, dig down
within your marked area to a depth of about 9 inches making
sloping sides so they don't cave in. This is a good depth
for shelves for marginal plants in pots. Now, leaving
the shelves, dig down to the depth you want, again with
the sides angled slightly. Your pond should be at least
2ft deep if you are planning to keep fish. That way in
very hot or cold weather, they can retreat to deeper water.
- Use a spirit level to
check that the sides are level all the way round. If this
is not done, you will have the pond full at one end and
not at the other so exposing the liner to sunlight.
- Dig a shallow section
all around the bank, just 1 or 2 inches deep to take the
overlap of the liner so that you can disguise and protect
it from sunlight.
- Remove all stones, roots
or other objects that could damage the liner.
- Firm the soil well inside
the pond including the sides and shelves.
- Line the pond with fibreglass
insulation, polyester matting, a thick layer of damp sand,
or old carpet. This will protect the liner.
- Now you put the liner
in the hole. The best way to do this is lay it out on
the ground for a few hours in the sun so that it is supple
and easier to handle. fold it twice, once lengthways and
once widthways, so that it is a quarter of its size -
now you know where the centre is. Place this part in the
centre of the pond and unfold it.
- Carefully push it into
position and anchor the edges around the bank with bricks
or other heavy objects (nothing sharp!). Turn on the water
and slowly start filling the pond. As the water pushes
the liner down into the shape of the pond, gently pull
the liner to eliminate large creases. If necessary, lift
the bricks so that the liner can move further down into
the pond. The inevitable creasing that occurs should be
guided into neat folds.
- Check that the banks are
still level and add or remove soil if necessary. Cut off
excess liner around the pond leaving no more than 6 to
9 inches and cover this with turf or paving stones in
mortar which should slightly overlap the edge of the pond.
You are now ready to start
populating your pond with plants and, if you choose, fish.
You can also landscape around it to encourage wildlife.
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