One of the major practical purposes of putting plants in a pond is to provide surface cover. This blanket of leaves serves two functions. Firstly, the growth of algae is discouraged by the shading effect of the foliage and this helps to keep the water clear by contributing to 'balance' — see page 111. Secondly, the fish are provided with cooling shade during the hot days of summer. Fortunately the larger surface-covering plants are also ornamental as they bear attractive flowers. Pride of place goes to the Water Lilies — you can extend both the interest and the flowering season at the centre of the pond by also growing Deep-water aquatics which, like Water Lilies, produce foliage which floats on the surface.
Of course it would be quite wrong to overdo the use of plants with floating foliage— you should aim to cover about one half of the water surface. This isdifficulttoachieve with newly-planted Water Lilies and Deep-water aquatics, and so Floaters are often introduced at theearly stage of pond development. Here the whole plant and not just the leaves float on the surface — some but not all Floaters bear flowers. Floaters are sometimes removed when the Water Lilies and Deep-water aquatics are fully established.
There is another practical job for plants to do in the pond Foliage absorbs both minerals and carbon dioxide from the water and this helps to starve out the algae. The Oxygenators are especially effective here — the leaves of these useful but generally dull plants are totally submerged.
The plants in the four groups dealt with so far have a practical purpose in the pond and most but not all have an ornamental value as well — another common feature is that each group contains only a small number of genera. The fifth group is quite different — the Marginals are shaliow-water plants which are grown close to the edge of the pond and have a purely ornamental function. There is a iarge number of genera and an extensive range of species and varieties from which to make your choice — a feature shared with the sixth and final group, the Bog plants. These moisture-loving plants which grow at the pondside require damp but not continually waterlogged soil in order to flourish.
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