MAKING A GARDEN POND

MAKING A GARDEN POND

A music critic once remarked of one of the great sopranos of long ago (Amelita Galli-Curci), that her voice always reminded him of ‘water-lilies floating on water’. What the critic had in mind, of course, was an effortless, unblemished beauty, serene and chaste. It is what has made sopranos and water-lilies revered down the ages.

Water-lilies, however, differ from most prima donnas in one important respect. They do not require cossetting, are by no means temperamental. In fact, water-lilies are extremely easy to grow, as are many water-loving plants. And for the newcomer to gardening, a garden pool probably offers more certain and more rapid results than any other form of gardening. Once the initial work is completed, a pond involves less maintenance than, say, the equivalent area in grass, and much less work than a herbaceous border. Moreover, a pond can occupy a tiny space where a herbaceous border would look out of place or awkward. On the other hand, a pond can be made the centrepiece of the most ambitious combination of rockery and stone and brickwork. No other form of gardening has such wide appeal. No child can resist rushing to the pond’s edge to watch the fish and glimpse the creepy crawlies. There can be few adults, even those normally indifferent to garden plants, who will not respond to the beauty of the water-lily. And even the non-gardener is likely to find afternoon tea or an aperitif, taken by the pond, somehow tastes different. There is perhaps only one drawback to a water garden; and that, to be sure, is a serious one. It is simply not true that it takes half a metre of water to make a hazard for a small child. Even a puddle is a potential danger to any child who cannot swim, and that fact should never be forgotten. But that said, probably no other kind of garden is more likely to appeal to all your family; to become, indeed, a family institution.

Tub ponds

A taste for water gardening need not be an expensive one. Long gone are the days when a wealthy landowner would take it into his head to install a pond of solid lead; but one of the oldest forms of containers is still among the cheapest. Half a wooden wine barrel will make an excellent tub pond. Standing on a patio about waist high, a tub pond makes an attractive ornament in its own right. Sunk in the ground, the pressure of water within and that of the earth without will keep the wooden staves of the barrel holding water long after the metal rims have rusted away. A sunken pond is not as susceptible to changes in air temperature as a raised one, a feature for which water-lilies tend to be grateful. And there are miniature water-lilies which are well suited to the small surface area contained in a barrel. The limited growth of these plants means that their leaves will not flop helplessly over the sides. An old china sink would do as well as a barrel — indeed any container which is at least 30 cm. Deep and which holds water will serve as a tub pond.

Prefabricated ponds

Next in convenience, though a great deal more expensive, is the modern prefabricated fibreglass or plastic pond. These are usually designed with ledges upon which can be placed baskets to contain marginal plants. Digging out the site to conform to the irregular shapes of most prefab ponds requires a little more skill and care than does a perfectly round barrel or a rectangular pond. Dig out the site as closely as possible to the shape of the pond, at the same time removing any sharp stones. The base and sides should then be given a surface of damp peat or sand. Upon this the prefabricated pond is bedded down and it is then immediately ready for filling. A disadvantage of prefab pools lies in their limited size; and more than that, the fact that you cannot choose or design the shape yourself which is surely half the fun.

Pool liners

No such drawback exists with what are called pool liners. These are largely made of plastics such as polythene; PVC (polyvinyl chloride); PVC laminated with a nylon weave; and Butyl rubber. PVC, whether it is reinforced or not, and Butyl rubber have the advantage of being stretchable. But all the materials are flexible and will snugly fit any shape. Too many abrupt contours and narrow inlets should, nevertheless, be avoided as it means overlapping the liner rather excessively. Besides, too many nooks and crannies, and small bays make a pond look fussy. Before cutting a single sod, map out the circumference of the pond you have in mind using a length of rope. (You might begin by putting your plan down on paper.) Remove the grass sods or the first few centimetres of soil within the area of the rope and you then have a blueprint of your pond. Any final modifications should be carried out at this stage. There is no difficulty about cutting out additional space in the pond later. But banking up crumbling soil to fill an unwanted corner or to make a promontory is much more trouble than leaving firm, well-packed soil where it stands. The same applies to ledges. When digging out the site, where you want ledges leave 30 cm. Or more of bank between the rope and the excavation. Then remove soil from the bank to a depth of about 20 to 25 cm. Finally, all sharp or flinty stones must be scrupulously removed from the site before installing the liner. By adding a few centimetres of sand — easily applied when damp — to the base and sides, it will be possible to stand in the finished pool without fear of damaging it — provided you wear soft-soled shoes. Similarly, heavy ornaments, if their bases are quite smooth, can be left to stand on liners quite safely.

Irrespective of how many ledges and contours are contained in your final layout, the dimensions of stretchable liners can be calculated in the following way. The length of the liner will consist of the maximum length of the pond plus twice the maximum depth. The width of the liner will consist of the maximum width plus twice the maximum depth. For example, a pond 2.4 x 1.9 x 0.9metresdeep, would need a stretchable liner 4.2 x 3.7 metres. If it is a non-stretchable liner you are installing, then the measurements must be taken more painstakingly. Run a tape measure from one bank over the ledges across the length of the base and up the bank at the far side. Do the same across the width. To both of these measurements add about 60 cm. So that the liner can be held in place under paving stones or rocks around the edge of the pond.

To install a stretchable liner, simply lay it across the site with bricks holding it around the sides. Then direct a hose pipe into the centre of the pool and watch the weight of water carry the liner down to the base and cling smoothly to every contour around the sides with the minimum of wrinkling. As necessary, you can aid the process by allowing the liner to slide gently from under some bricks and pulling it up further under others. In cold weather the elastic quality of the liner may be reduced. This problem can be solved by leaving it in a warm room for some hours, if you wish near, but not in contact with, a radiator. To install a non-stretchable liner, lay it in the site and smooth it over the contours, slowly adding water all the time. Once the pond is full of water, the edges of the liner can be trimmed and held in place permanently by a layer of concrete or paving stones.

While PVC and Butyl rubber are about five times as expensive as polythene, their life ex-pectancy is much greater. Even the heavier grades of polythene are not to be recommended for permanency. Quite apart from what may happen to the polythene below water level, the area above the water line will be subject to the ultra-violet rays of the sun and these quickly make polythene brittle. The other kinds of liners are nothing like so vulnerable to the sun’s rays and they last many, many years. Liners are available in various colours. Grey, often called ‘stone’, and black are the least conspicuous and so are the most natural colours. Blue, especially light blue, should be avoided, as it clashes badly with plants. And upon all underwater surfaces algae will adhere and grow, and blue shows up this growth. Some liners may be more algae-resistant than others, manufacturers at least claim as much, but it is only a question of degree. Sheets of Butyl rubber and PVC are normally sold in standard sizes. But these sheets can be vulcanized or welded together by the manufacturer as required. So virtually any size or shape of pond can be accommodated. It is also possible to tape sheets of liner together yourself, but the welding process is to be preferred. Puncturing is the worst problem associated with pool liners. However, repair kits are available for Butyl rubber and PVC. Polythene cannot be repaired satisfactorily.

Concrete ponds

Cracking is the main danger concerning concrete ponds. The unyielding strength of concrete is both its virtue and vice. Should the sides or base of a concrete pond be placed under greater stress than they can endure, the result is inevitably a crack. And even if that crack be no more than a hairline one, there is no certainty about the repair. Large cracks will be even more troublesome. A concrete pond may be the most durable of all, but this is only so if it is built to the highest standards in the first place. Compromise on the preparation of site, in the thickness of the concrete, omit reinforcement in the concrete, fail to allow for the expansion of water into ice, and disaster may well follow.

To begin with, satisfy yourself that the site is firm and stable. If in doubt thoroughly bed into the base and sides a layer of coarse aggregate (gravel). In an informal pond the sides should be cut so as to slope outwards at an angle.

It starts by pouring the concrete over the base. Place the reinforcement over this and then add concrete to make up the final thickness of 15 cm. Make sure that the wire mesh is completely smothered in the concrete without protruding at any point, except around the banks where it will be used to reinforce the sides. In the case of an informal pond, it should be possible to concrete the base and sides in one single operation. With small, formal ponds you may be able to put the shuttering in place while the base is still soft and so proceed immediately with the sides. (It really depends upon the weight of the shuttering and whether it can be installed without the necessity of walking on the base.) If you cannot put the shuttering in straight away, key or roughen the edges of the base to make a good joint with the sides later. Allow the base to harden, install the shuttering and add the walls. Old concrete will not bond with new, so the sooner the walls are added the better — I would certainly not leave the adding of the walls for weeks on end. Also, the earth banks will tend to crumble to some extent and it is imperative that you do not get soil mixed with the concrete at any stage. The fact, incidentally, that you have dampened the walls should help. And if the weather is very hot it is as well to lay wet sacks over the concrete while it hardens. The more slowly it loses moisture the better the concrete. Indeed it is worth filling the pond with water after twenty-four hours.

Calculate the amount of concrete you need by adding the surface area of the four walls to the area of the base and multiplying that figure by the thickness you intend making the concrete. For example, if you were making a pond 5 m. x 4 m. x 0.9 m. internal depth with the base and walls 15cm. Thick, the calculations would be made as follows:

2 (5 x 0.9) = 9 sq. metres (the two longer walls)

2 (3.7 x 0.9) = 6.66 sq. metres

(the two shorter walls) i.e. each length less 2 x 0.15 cm. Which is the thickness of the longer walls

5×4 = 20 sq. metres (the base)

The total surface area therefore amounts to approximately 36 sq. metres. Multiply by the thickness: 36 x 0.15 = 5.4 cubic metres, which is the amount of concrete the pond requires. Ready-mix concrete becomes economical for any size of load above 3 cubic metres. And one would be well advised to have so large a load as 5.4 cubic metres supplied by a ready-mix company provided, of course, that the lorry can approach the site. Failing that, look into the possibility of hiring a small, portable cement mixer. In this case add half the coarse aggregate and half the water first, then add the sand. Once they are mixed, add the cement and finally the remainder of the coarse aggregate and enough water to produce the necessary consistency.

If you are buying the materials to mix yourself, then they should be calculated as follows. The ratio of the mix is 1 cement : 2 sand : 3 aggregate, that is to say there are 6 parts to the whole. Therefore, in 5.4 cubic metres one part will consist of 5.4 -J- 6 = 0.9cubic metres. So one needs:

0.9 cubic metres of cement

1.8 cubic metres of sand

2.7 cubic metres of coarse aggregate

You may find that the builder’s merchant supplies the materials not according to cubic capacity but according to weight. Unfortunately, there is no fixed ratio between the weight and cubic capacity of either sand or coarse aggregate. The ratio varies according to the character of the materials. It is better to use the density of concrete as a unit of measurement. (This is not absolutely accurate, but it is quite sufficient for pond building.)

The density of concrete can be set at 2.45 metric tons per cubic metre. So for 5.4 cubic metres the weight would be 13.23 metric tons. The materials can now be calculated as follows:

CEMENT13.23 = 2.205 tons

Each bag of cement weighs 50 kilos,

so 45 (44.1) bags are required.

SAND: 13.23 x 2 = 4.41 (say 5 tons) 6

AGGREGATE: LL?! X 3 _ 6 615 (7 tons)

It is always safer to slightly overestimate your needs to allow for wastage. Remember that the number of joints should be kept to a minimum. Try to complete the pond in no more than two operations.

If you live in an area with very severe winters, you can make a concrete pond of great strength by employing a technique more usually used for swimming pools. It consists of building a double wall of concrete blocks and filling the gap between the two walls with solid concrete. Steel rods can be inserted in the blocks as they are laid and this will provide massive strength. The blocks will not be waterproof, they simply provide the strength. It is the concrete between the two walls that makes the pond watertight and it must be very thoroughly compacted. An important point to note is that when laying the blocks, surplus mortar must not be allowed to collect on the base between the two walls. If it does, the inner concrete wall may not make a watertight joint with the base.

This is an expensive method of pond building and a time-consuming one. As against that, it does mean shuttering is avoided and this is worth bearing in mind where large-scale, geometric designs are concerned.

Whereas with fibreglass and liner ponds it is usually possible to make some adjustment to the level of the walls after the pond is completed, with concrete structures it is never possible. Nothing looks worse than water halfway up one bank and brimming over the other. Building up the offending wall is useless as the bond will not be watertight. So it is worth taking the trouble to level the site before carrying out the concreting. Use a straight board and a level. If the site is too large to stretch the board from one bank to the other, drive a stake into the centre of the base so that it is level with the lowest bank. Then remove the surplus soil from the other banks, taking readings with the board and level as you go.

Alkali will leach out into the water from new concrete, and this is harmful to both plants and fish. It can be prevented by painting the interior surfaces of the new pond with a sealing agent. Alternatively, the new pond can be ‘cured’ by filling and emptying it of water several times over a period of some weeks. The addition of enough permanganate of potash to colour the water purple, or acetic acid, will speed up the process. Apart from the curing process, you may want to empty the pond from time to time. The old idea was to dig out a pit, fill it with cinders or rubble, and run a pipe from it to the pond. In very porous soils, it was sometimes suggested that no more than an outlet pipe — perhaps composed of the top half of a bottle with a rubber stopper — would be sufficient. None of these ideas is to be recommended, for several reasons. Apart from the additional work involved in digging out another pit, if the outlet pipe becomes clogged it will be almost impossible to clear it. And above all, if the joint between concrete and pipe is not perfect or leaks later — what if you crack the top of the bottle? — it cannot be rectified. It is a far more satisfactory practice to use an electric pump.

Finally, you are bound to have mused over how deep to make your pond. Deep ponds are more attractive than shallow ones, but the main consideration is the depth of water that various water-lilies like over their crown. Generally speaking, if one allows a depth of 20-30 cm. For the soil and 45-70 cm. For the water above the soil, that is sufficient. In other words a total depth of between 65 and 100 cm. Only so far as large water schemes are concerned is it worth increasing the depth above one metre.

These then are the available means of making a garden pond. Having decided upon the materials you wish to use, the next stage is to consider design possibilities.

Sorry, comments are closed for this post.