How Fertile is the Soil in Your Garden

The next point is to find out whether there are sufficient nutrients available for the plants in the soil. There are two practical ways of doing this, by having the soil tested and by observing plants already growing on the site.

 It is possible to have the soil tested commercially by a number of firms, or alternatively small kits can be purchased. These will give an approximate indication of the relative fertility of the soil. Before using any figure or recommendation gained by soil testing, you should consider the type of plant you will be growing in the area. The recom­mendations usually given with the types of soil testing kits available in many garden centres are appropriate to most vegetable plots but are too rich for shrub beds and a number of plants.

Observation of plants growing on the site can be a very effective way to gauge the fertility of the soil. It requires a modicum of knowledge as to what the plant should look like, but comparison with the same plant in a neighbour’s garden will go a long way towards answering whether extra nutrients are needed. It the plants in your garden have much smaller leaves and poor fruit compared to others of the same form elsewhere, it is likely that yours are deficient in some nutrient (although you should first consider the possibility of a fungal infection to the roots). If however, they are large, leafy and barren, it is likely that your plant has too much nitrogen and either no fertiliser should be applied, or only potassium and phosphorus should be given. The simplest cases are where the plants are showing some deficiency symptom.

Where there are no plants growing on the site, it is possible to obtain an indication of the fertility of the soil from observing weed species. For example, sheep’s sorrel indicates a very acidic soil or surface layer, as does natural ling or heather; nettles indicate freely available nitrogen. These and other indications can be gained from reference to a wild flower book which gives details of the natural ecology of the weeds or wildflowers.

Most gardens soils are not short of nutrients, although additional fertiliser given as a balanced feed at a low rate will often encourage better all round growth. The main exceptions to this are where special groups of plants are being grown, such as rhodo­dendron, and on very acidic or alkaline sites, where nutrient availability may be affected by the pH. The application of lime can be used to raise the pll and that of sulphur to lower it.