The pH scale is a scale of value for the itogree of acidity or alkalinity of a soil. Soils below 7 are regarded as being acid, those above 7 as alkaline. A pH value of 7 indicates a neutral soil and an ideal garden reading is 6.5. Below 6 on the agile the extreme acidity of the soil makes it sai:able only for acid-loving plants such as lithers and rhododendrons. A reading above 8 means that the soil is so alkaline that it will support few plants, due to essential foods being ‘locked up’ in the soil. However certain plants, such as carnations, sweet peas and onions, do prefer alkaline conditions.
One way to discover a great deal about soil-its type and fertility-is to observe the plants that grow in it naturally, including the weeds. There are also various home kits v.hich test the acidity or alkalinity of your soil. Some register the pH value as a colour variation. It is advisable to take samples from various parts of the garden, as the level of acidity may vary from one area to another.
The level of acidity or alkalinity can be controlled by adding lime, peat and various chemicals such as sulphate of ammonia to the soil. Lime helps reduce the acid level of a peaty or sandy soil while peat and sulphur make a chalky soil less alkaline. One of the best ways to improve your soil is to dig it, using a good spade or a fork for heavy clay soils. Digging will aerate the soil, kill the weeds and break up some of the subsoil so that the layer of topsoil is gradually increased. It should be done once a year, and autumn or early winter is the best time. This is particularly important with heavy clay soils, so that winter frosts will break up the compacted lumps and prepare the ground for planting in spring.
The depth of topsoil varies. A site recently left by a builder may have no topsoil at all (or it may be covered by the subsoil layer), while in parts of the Mississippi Basin the rich alluvial deposits are 6 m (about 20 ft) deep. The average garden has between 300 mm and 600 mm (1 ft and 2 ft) of topsoil, but a depth of as little as 150 mm (6 in) is sufficient for growing a large number of plants. You can test the depth of topsoil by the use of a soil auger, a tool like a giant corkscrew, which will bring up a sample of the soil profile, the several layers from which it is formed. A simpler test is to dig a hole with steep sides and so make the soil profile visible in that way. The hole will also show you how quickly the top- or subsoil drains after rain.
For the revitalization of an old garden, many writers suggest removal of the soured topsoil and its replacement with new, but this is both difficult to obtain and expensive. (On the basis of the calculation that it takes 25 mm-1 in-of topsoil a thousand years to develop, it is, of course, cheap.) When buying topsoil, it is important to establish its Source and to be sure that it is `vegetable’ topsoil, with organic content, and free of disease and weeds. Beware especially of the roots of weeds such as couch grass. A period of deep cultivation and the addition of plenty of organic material will increase the amount of topsoil already in a garden by encouraging bacteria to work within the top layers of subsoil.
However it is laid out and whatever individual requirements it meets, a gar should always serve as an extension of house. It should be seen as an outside rooms where suitable activities can take place-from shelling peas to tinke. with a motor cycle. During warm summer months the garden may well be in aim, constant use, not only for sunbathing also for family barbecues and outd entertaining.
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