Before buying plants it is as well to consider the alternative methods of planting open to you and decide which technique you intend to adopt. There are two possibilities. One is to cover the floor and shelves of the pool with a soil layer about 6 in. deep. This offers those plants which are so inclined – and many aquatics are – the freedom for an orgy of growth, and it gives the fish a muddy bottom to stir up to their hearts’ content. The result may well be permanently muddy water half choked with the abundant growth of the more aggressive reeds and rushes. The alternative, and I strongly recommend it as having many practical advantages, is to plant in containers and to have no soil at all outside the containers. Roots then have little encouragement to stray and can easily be spotted if they do; plant growth is confined to tidy clumps which can easily be re-arranged if you wish to experiment with different colour associations; fish have much less chance for mud stirring, and none at all if thesoil is topped with gravel or pebbles; and, of course, much less soil is needed. The greatest advantage will show itself if, after a few seasons, the pool needs a general spring clean; there is a power of difference between lifting out a dozen planting baskets and shovelling out several cubic yards of liquid mud.
Suitable plastic containers, which last so much better than boxes, are not expensive. The most popular are square, with sides sloped conveniently to fit the recommended 20-degree slope of pool walls.
The container sides are generously perforated to allow the essential interchange of dissolved gases between soil and water. If the soil used is loose or very fine, and there is continuous water movement caused by a waterfall, perhaps, or even by the activities of many fish in the confined space of a small pool, there may be a gradual erosion of soil from the container, muddying the water. In such circumstances it will be beneficial to line the container with permeable material such as hessian (provided it is not treated with preservatives) or bits of old sheets or curtains. If thin polythene (such as vegetable bags) is used it must be punched full of small holes. Generally a lining of turf, shaved as far as possible of grass, will prove satisfactory.
The use of clayfor aquatic plants usually results in sour soil and stunted growth and should be avoided. Plastic shaped like traditional clay pots, even though perforated, have so little stability they are easily nudged over by fish, and for marginal plants which have breeze-catching foliage above water they are useless.
Pond plants are extremelyin almost any soil, probably because many of them absorb dissolved mineral salts direct from the water through their and and are thus only partly dependant on . They revel in heavy soil – yes, even clay – but accept any reasonable garden loam. What they do not require is peat, , sand, -mould or general garden fertiliser. Too much growth rather than not enough is usually the problem with aquatics, and I see no point in giving them manure and bonemeal which they do not need, but which will certainly encourage the growth of algae. The only additive I would consider is Lily-Grow, a non-nitrogenous fertiliser containing phosphates, which are deficient in many soils, in a slow-release form designed for aquatics.
CHOOSING YOUR PLANTS
Someplants are purely decorative, some are grown simply for the sake of their contribution to pool balance and ecology, while others are both beautiful and functional. How many of each type a pool needs is usually calculated on the basis of the pool surface area. Disregarding for the moment the question of individual varieties, which later chapters will describe, let us look at the different types of plants and their general characteristics.
Wherever planting depth is mentioned, below and hereafter, it should be taken to mean the depth of water above the level of the soil in which the plant is growing, and this can be quite different from the depth of the pool. A lily planted in a container 8 in. deep standing on the floor of an 18-in. Deep pool is growing at an effective water depth of 10 in. If the container is supported 3 in. on bricks the effective water depth is 7 in. If it is growing in mud on the bottom of a natural lake 2 ft. deep, the planting depth is, of course, 2 ft.