Since the introduction of fiberglass pools tremendous interest has been shown in medium-sized garden pools.
Siting the pool Before constructing any pool careful thought should be given to the siting. To create a successful bog garden or water garden, it must be situated right out in the open, in full sun. Although not essential it is advantageous to give protection from the north, if possible, as this will extend the flowering period both in autumn and spring. A belt of trees, a hedge or buildings on the north are all suitable. Overhanging trees are a disadvantage, both because of the amount of shade they cast and on account of their leaves, which will undoubtedly fall, in the water during the autumn. Weeping trees, although aesthetically pleasing in their early stages can mar a pool in a few years, as without sunlight you will get leaves on aquatic plants, but no flowers.
Give consideration also to the water supply, whether this is natural or artificial. Generally speaking large quantities of water are not required after the initial filling. Even in a discolored pond you should not continuously run in fresh water or make frequent changes, as this tends only to keep the water murky. Provided the pool can be reached with a garden hose a normal domestic supply is quite adequate. Drainage should be considered but is not very important, provided there is lower ground nearby or a drain on a lower level, into which Water can be siphoned or baled during emptying.
Paint the pools in dark or natural colors, and try for a general natural effect. The edges may either be disguised with plants, paving or stones, which should slightly overhang the water. Or you may cover the edges with Myriophyllum proserpinaco ides, a very rampant grower. As it is sometimes destroyed by frost, a pan of young cuttings should be removed to frost-free quarters in autumn.
Deep water aquatics Great care should be taken in the selection and subsequent planting of nymphaeas (water-lilies). Shallow-water, marginal aquatics require plain loam, and bonemeal should be added only when the soil is poor, as most of these plants are difficult to keep within limits. Most water plants flourish freely if they are planted directly on the base of the pool, but many fiberglass pools do not retain the soil on the shelves, and the plants may have to be put in containers. The main advantage of planting directly into a soil base is that most of the plants remain undisturbed for four or five years (except for thinning operations) whereas in containers they have to be repotted every third year. On the other hand, it is much simpler to lift and replant containers than resoil the whole pool. Choose large plastic containers, or make them from 2.5 x 2.5cm (1 x 1 in) timber nailed together with 2.5cm (1 in) spaces between the slats, or you can use old wicker baskets.
Tall marginal aquatics, such as Scirpus albescens , should be reduced in height to 23-25cm (9-10in) to prevent them from being blown over before the roots have obtained hold. Underwater or oxygenating aquatics need only be pushed into the soil in the deep parts of the pool or planted in containers beside the water-lilies, etc. Most marginal requires slight thinning each year, especially some of the more vigorous varieties. Most spread readily and small pieces can easily be removed and replanted.
The nymphaeas are by far the most important deep water aquatics, but there are a few other plants in this section worthy of mention. These may be grown in formal pools on their own or informally with the water-lilies.
Sometimes they succeed where waterlilies fail because of overhanging trees or insufficient room for the latter to develop. The genera Aponogeton and Nuphar contain suitable species.
Hardy marginal aquatics The majority like to have their roots covered with 5 to 7cm (2 or 3in) of water, although some will grow in more and others are perfectly happy in permanently wet soil. Suitable species will be found in the following genera: Acorus, Butomus Caltha, Cotula, Cyperus, Eriophorum: Iris, Juncus, Menyanthes, Mimulus, Orontium, Pontederia, Sagittaria, Scirpus and Typha . .
Submerged and floating aquatics These are vital for the well being of the pool to correct balance and obtain clear water. Oxygenating aquatics replace lost oxygen to the water and provide cover and a breeding ground for the fish. Many oxygenators are very rampant and so have to be kept in check. This is not difficult; the garden rake should be forcefully pulled through the underwater vegetation when it is becoming overcrowded to remove all surpluses. It is advisable to introduce four or five different varieties of oxygenating plants at one time. It will be found that some will grow at an alarming rate and others either stand still or die. This will have no adverse effect, as those that are growing well will do the work of the less vigorous varieties.