March 26, 2013

Build your own garden pond

Build your own garden pond — your own (edible) mini-wetland. The pond was complete now, and when he saw the tall, sleek heron standing there he thought how good it was that his garden pond was starting to attract birdlife. Suddenly, the tall wading bird dipped its head towards the pond and when it came up with the gardener's expensive coy carp in its beak, he was suddenly less impressed. The pond had succeeded in attracting wildlife but providing free meals for passing herons wasn't quite what the gardener had in mind.

Most peoples' experience with garden ponds is less dramatic, however, like that gardener's pond which once housed his favourite fish, they are a way to bring wildlife into your garden.

The opportunity to learn to make a small garden pond was what crammed 22 people into the Barrett House sustainability and community centre in Randwick in early February this year. The workshop was one of a continuing series organised by the Eastern Suburbs 3-Council Ecofootprint program which provides a DIY approach to small scale sustainability in the home and community. It was taught by landscape architect/permaculture educator, Steve Batley.

That there could be so much interest in making garden ponds is surprising, as was the enthusiasm of participants. Their motivations for attending the workshop ranged from the intention to make a small pond in their garden to a woman who plans to convert her disused swimming pool into a rather big pond.

Why ponds?

There's nothing quite like it — peeled of their dark brown skin to reveal a white flesh, biting into one of these crisp water vegetables is to experience it in a way that makes its canned version seems far inferior. You can slice it into a stir fry and enjoy it cooked too, and I'm sure you home chefs out there would be able to devise other ways of preparing the water chestnuts you have picked from the pond in your garden.

There are other water vegetables you can grow in your home or community garden pond — fresh, crisp water chestnut is only one of them. And there are reasons other than food to make a garden pond. One of these is to provide a resource — water — that helps establish your own home or community garden wildlife food web.

Standing water attracts insects, which attract those larger creatures that feed on those insects, such as skinks, blue tongue lizards and small birds. A DIY home or community garden pond forms the basis for your own wildlife zoo where you can see nature in action and where your children can learn about how nature works better than any text book can teach them.

It's croaking frogs that many people want in their ponds, however not everyone is happy with a froggy chorus to end the day with. There's the story I was told of the unhappy neighbour who complained to their council about the croaks coming from the garden next door. Council had the gardener remove the amphibians so the neighbour could hear more pleasant sound, like her TV, presumably.

Design the important ingredient

We can't simply plonk a pond anywhere we want. Like everything in the garden, installing a pond is an exercise in design.

Design starts with site analysis, a process that looks at the conditions prevailing in your garden and how influences like sunlight, winds and runoff coming in from outside can affect it. In site analysis, we look at sunshine in the garden and estimate it for summer and winter, we look for areas of shade and we check out the topography of our garden... whether the land is flat or sloping and how steep that slope might be.

Think about rain and how the runoff flows over your land, remembering that water flows to the low point of your garden. What you are watching for is the possibility of contaminated water, perhaps containing eroded soil, flowing into your pond. If you are not an organic gardener, that overland flow could carry synthetic garden chemicals into your pond and this could kill the microlife in the water. Nearby tall trees can become difficult when they drop too many leaves into the pond where they decompose, contaminating the water.

Our site analysis findings influence where we place our pond, which prefers a position that is 60-70% shaded. This will reduce water loss due to evaporation. It's best to avoid the heat of the afternoon summer sun when we think about water loss.

All those little creatures that gather around your pond will appreciate the shade too. Consider that a site that appears good in summer may be shaded and cold in winter, so think of how sunlight moves across your garden in winter when the sun is lower in the sky. Remember we want shade for the pond in summer but we don't want it freezing in winter.

Design

Take a look at the small pond in the edible cottage garden at Barrett House. You'll see that it's surrounded by plants — herbs and vegetables as well as large stones — and that these shelter it. Look at the water surface and you'll see that, between the edible Lebanese cress growing from pots submerged below, the surface is largely covered by the nitrogen-fixing azzolla, a plant that you can scoop out and use to fertilise your pot plants when it starts to get too thick. The azolla reduces the area of open water where mosquitoes leave their larvae, too.

How deep do you make your pond?

A starting point to thinking about this is to remember that shallow ponds will lose their water to evaporation quickly. Too deep a pond, however — more than 30cm — will require fencing, a legal stipulation to prevent children falling in.

There's two ways to install a garden pond — use recycled materials like an old plastic childrens' pool or bathtub or buy a moulded, preformed, fibreglass or plastic pond or dig your own. The commercially available, moulded type come with variable depths and corrugations already installed. You simply locate the best place for it, dig a hole and install it. They're the easiest way to acquire your own mini-wetland in your garden.

Build it yourself

Here's how to make your own pond. The tools you will need are a spade, a spirit level and a means to fill the pond, such as a hose or bucket and a tap.

What follows describes installing an in-ground pond, however you can make a pond that sits on rather than in the ground. For this, you will need a large planter (see photograph below), an old metal bathtub or some similar, strong and waterproof container.

This is how you make it:

  1. Dig a hole to size and shape. If you are using a moulded pond liner or converting a discarded metal bathtub or tub (such as one of those discarded, small, solid plastic child's swimming pools) into a pond, that will dictate size and shape of the hole you dig.
  2. Place a layer of river sand, around 25mm deep, in the hole to prevent sharp objects in the soil puncturing the pond liner.
  3. Place the pond liner in the hole you have dug. Pond liners comes in different thicknesses and this could influence their useful life. Liner is expensive, so making a price comparison between liner and moulded pond might be worthwhile. Avoid using builder's plastic as it punctures easily.
  4. Use a spirit level to ensure the pond is sitting level.
  5. Carefully (to avoid puncturing the liner) place sand and a little gravel in the bottom of the pond so the pots holding your water crops sit on it and avoid puncturing the liner. Some people place hessian bags on top of the liner to form a soft barrier then put the sand and gravel over that.
  6. Place pots with plants into your pond. So, what grows in water, looks intriguing and is edible?

Duckweed is a surface water cover that will reduce open water available to mosquitoes for depositing their larvae. Rather than viewing mosquitoes as a pest, you might consider their larvae as food for small fish that can be introduced into a deeper pond. White cloud minnow and pigmy perch are suitable species.

Azolla is another dweller on the pond surface that will grow to form a mat. In its roots that hang in the water below it forms an association with blue-green algae and extracts nitrogen, an important plant food, from the water, This makes it worthwhile to occasionally scoop the azolla from the pond and place on your pot plants as a living fertiliser.

Water chestnut is a root crop that is well worth planting. It is ready to harvest and eat in winter, the brown corm being the part you eat, raw or cooked.

Lebanese cress is a leaf crop eaten raw in salads. It can be grown in a pot immersed in the pond.

Kang kong or water spinach is another leaf crop that is cooked. It is a bog or wetland plant grown in soil kept moist immediately surrounding the pond and can be grown in a pot standing in the pond.

Duck potato or arrowhead — so named because of its leaf shape — is a root crop, eaten cooked.

Watercress is an edible leaf eaten raw in salads. It could be cooked too.

There are other wetland plants you can establish in pots in the pond or in the soil immediately surrounding it, such as the native sedges.

  1. Fill the pond gently. Some gardeners are wary that the chlorine in tap water could discourage insects and microcreatures in the pond. If you use tank water this is not a factor. What some pond makers do is to pour tap water into a container and leave it sit between one and five days so the chlorine will outgas.
  2. Plant around the pond so as to create habitat for frogs, birds, lizards, insects... the whole food web. A few small logs and large rocks set up the nooks and crannies that small creatures find refuge in.
  3. Now your garden is built and filled and pots containing your water plants installed, you move into the next stage — maintaining your pond garden. Keep the water level up and try to identify the creatures that come to live in and around or that visit your pond. Children like doing this. Buy a magnifying glass to see the wildlife closeup, and a guide book to identify them. Learning, as well as food, can be a yield from your pond wetland.

Your own mini-wetland — more than a good idea

It's your own pond, your own mini-wetland, and it's of benefit not only to hungry humans but to the wildlife we share our cities with as well. That was one of the messages that people attending the pond makers workshop at Barrett House took away.

So, now, that woman who used to transplant tadpoles only to see them disappear, and that other woman who wants to turn a swimming pool into a somewhat large pond will have a few clues on what they can do. But for that man who lost his prize carp to the heron... well, there's not much we can do for him other than suggest netting his pond against big birds. So where do you buy heron netting?

If you're around Frenchmans Road, drop into Barrett House (6 Barrett Place) to check out the little pond. Come on the morning of the first Thursday of the month, to one of the monthly open days, and you can get advice directly from the landscape architect who installed the pond. In the meantime, enjoy your mini-aquatic adventure in pond construction and enjoy trying some tasty wetland foods.

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Story and photos by Russ Grayson

If you have a sustainable story to tell, email it in along with a couple of photos to info@reduceyourfootprint.com.au - receive an eco switch for every story published.

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