How to Construct a Water Garden

The essential features of a garden pool Before buying or building a garden pool, it is essential to be aware of the requirements of future inhabitants. Waterlilies and other deep water aquatics require specially allocated positions in deep areas of the pool if they are to flourish, while marginal plants, such as reeds or rushes, are grown on a shallow shelf which extends around at least part of the edge.

Waterlilies will grow in widely varying depths of water according to their variety, some living happily in as little as 15cm of water, while others will tolerate in excess of a metre. Most of the popular kinds, however, grow best in 45cm of water and when a prefabricated pool is contemplated it is essential to see that such a depth is available together with ample level space on which to stand the planting containers.

Marginal plants occupy the shallows towards the edge of the pool. These should be about 20cm deep and sufficiently wide to accommodate a planting basket. Many prefabricated pools are made with very narrow, shallow shelves on which the plants are intended to be planted directly into soil or compost. But for reasons which I will explain later this is an undesirable practice.

Having made provisions for the plants we should not overlook the requirements of the ornamental fish. Fancy goldfish, such as telescopes and fantails, need a depth of at least 45cm of water if they are to over-winter successfully. But ordinary goldfish and carp will usually survive quite happily in a minimum depth of 20cm.

As with all other garden features one must plan well ahead. Decide as clearly as possible which plants and fish are to be accommodated and then purchase or construct a pool with their well-being in mind. A reversal of this procedure leads to endless trouble.

There is one other point that must be considered and which varies from one garden to another. This is pool size. It is impossible to say that a particular pool is suitable for one garden, for gardens, pools, and personal tastes are very different. But a pool that is either too small or too large for its surroundings is a blot on the landscape.

To get some idea of the size and shape necessary to give the desired effect, take a length of hosepipe or rope and form the outline of the pool on the site. This can be adjusted until one is satisfied. Measurements can then be taken and the method of construction decided upon.

Making a pool from a liner

Pool liners are one of the most popular forms of construction for they are relatively inexpensive and can be used to create any shape that the gardener desires. They are quite simply a large sheet of rubber or polythene material which is placed in an excavation the size and shape of the finished pool. The liner is installed and secured to the edge of the pool by rocks and paving slabs. Water is added and the liner can then be moulded to the contours of the pool.

There are many different kinds of pool liner in a widely varying price range. So many in fact, that the newcomer to water gardening is likely to be confused and make a costly mistake unless he studies all the sales literature very carefully.

Liners of 500 gauge polythene in a sky-blue colour and three or four standard sizes are the cheapest. These are intended for selling in quantity at the lower end of the market. While not condemning them completely, I feel that they have little to offer the serious pool owner as they have a very short life. Any gardener who goes to all the trouble of digging a pool and installing a fountain or waterfall and a collection of aquatic plants likes to see his creation come to maturity. This is extremely unlikely to happen with a polythene liner as it rapidly deteriorates.

This deterioration is most marked between soil and water level. If exposed to the rays of the sun the polythene bleaches, becomes brittle, and then cracks. Within a very short time pieces of stiff polythene fall away and the pool collapses. Of course, if the water level can be maintained so that the polythene is not exposed, then this problem can be alleviated. It is also worth noting that some aquatic plants can puncture a polythene liner with their spear-like creeping rootstocks. Reed maces (Typha latifolia) and bur reeds (Sparganium ramosum) being particularly adept at this.

The manufacturers of this type of liner claim that it will last for up to ten years. While this is possible with extreme care, the more usual life span is three or four years. So bear this in mind when being tempted by its low price. I would not condemn the liner completely though, for it does have its uses. Like marigold and nasturtium seeds which lure youngsters into gardening, the polythene liner encourages gardeners, who are perhaps a little sceptical, to sample the delights of the pool. Once bitten they invariably progress to more ambitious projects.

It can also be used for providing a quick and cheaply constructed sanctuary for ailing fish, a nursery for young aquatic plants, or somewhere to put the fish and plants when the pool is being cleaned out. For this purpose it is ideal.

Polythene liners should not be confused with those made of the similar, but more robust, polyvinylchloride (PVC) material. These are usually sold in several colours. Blue, stone, green, or imitation pebble, and some manufacturers produce them with blue on one side and stone on the other. Although not taken with the gaudy colours, I can recommend these as economical and durable liners which represent excellent value for the beginner.

An even tougher type made of the same material and available in similar colours is produced incorporating a terylene web.

This gives the liner extra strength and is undetectable once installed.

For the strongest material of all we have to turn to rubber. This is obviously much more expensive than any other type, but is virtually indestructible. Such is the confidence amongst farmers and industrialists that it is widely used in the construction of lagoons and reservoirs. Sunlight and frost seem to have little effect upon its black matt finish, and the only way in which it can be punctured is by accidentally sticking a garden fork through it. In addition, those who like the bright colours available in the other pool liners can transform the rubber kind with special nontoxic paints. Certainly any gardener seriously considering a permanent water garden would be well-advised to study the properties of this material.

Once the decision has been made as to the type of liner to be employed, it is then necessary to calculate the size of liner required. To do this, first measure the length and width of the intended pool. Or if it is to be of an irregular shape, the size of rectangle that will enclose the entire shape.

Then build up the calculation of the liner length and width as shown in the example which is for a simple formal pool of uniform structure and depth with a marginal shelf on all four sides. The calculation for an irregular-shaped pool follows exactly the same method.

Irrespective of the material used, lining a pool follows along broadly the same lines. The excavation is scoured for any sharp objects like flints and sticks which may damage the liner. A layer of builders’ sand is then spread over the pool floor to act as a cushion. If the soil is rough or stony then thick wads of dampened newspaper can be used to line the walls to prevent any projections from ruining the liner.

The excavation is then ready. If the liner is of the polythene variety it should be spread out in the sun for an hour or so in order to become pliable and easier to work with. It will still have little elasticity and must therefore be installed without water being added, allowing plenty of room for movement so that when water is introduced the liner can be more easily moulded to the shape of the pool. Unsightly wrinkles often occur with polythene and these should be dealt with as the level rises. They are impossible to straighten out once the pool is full.

A slightly different technique must be adopted for PVC and rubber liners. These are more flexible and can be stretched out evenly across the excavation using bricks or paving slabs to hold them in place. Water is slowly added and as the liner tightens the anchoring weights are slowly released until the pool is full and the liner pressed to the outline of the excavation. When full, any surplus material can be trimmed, but about 30cm allowed to remain for securing with paving slabs or rocks. Once the edge is neatly finished the pool can be planted, for none of the specially manufactured pool liners contain anything that is toxic to plants or livestock.

Before departing from pool liners I should mention that they are invaluable for making a bog garden. We have all thought of making an excavation and lining it with polythene. Then refilling with a suitable peaty mixture and planting moisture-loving plants. This is reasonably successful, but a proper bog garden can easily be contrived by the gardener who is making his pool from a liner. He must, of course, allow for the extra material necessary at the time of purchase.

The idea is to construct the bog garden adjacent to the pool by making another shallow excavation like a huge marginal shelf. This should be of the order of 30cm deep. The pool liner is then used to line the excavation and the shallow bog area in one piece. A barrier of stones or bricks can then be placed across the division between pool and bog. This will retain the soil in the bog garden and yet allow water to seep through. It is essential when refilling the bog area, that the level of the soil is well above that of the water or else it will just become an extension of the marginal shelf.

I have only come across one problem with this kind of bog garden and that is waterlogging. It seems that if moisture-loving plants are sitting permanently in saturated conditions they will not prosper. To overcome this I find it essential to provide a 6cm layer of coarse gravel on the floor of the bog. Then a mixture of peat and soil is added as the growing medium. The gravel then acts as drainage and a reservoir. If the plants can grow with their collars above the water and yet dangle their roots into it they seem blissfully happy.

30. July 2011 by Dave Pinkney
Categories: Gardening Ideas, Water Features | Tags: , , | Comments Off on How to Construct a Water Garden

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