Garden Soil Testing

Need for soil test

There are two thoughts on this. Some gardeners leave well alone until something goes wrong. Others test every part of the garden with complicated gadgets that will tell them everything about the soil content. The happy-go-lucky gardeners are run­ning a risk. All plants have basic needs and require a decent environment and a good standard of management to enable them to succeed. On the other hand, those scientifi­cally minded gardeners who use gadgets to determine every trace element in their soils may well be wasting their time, because for most plants, minute variations don’t matter.

The aim of all gardeners is the same: to produce strong and healthy plants. A lucky few manage this with the minimum of bother and expense, but a lot of people are dissatisfied with the results of their labours, and it might well pay them to carry out an acidity test.

The test may show that your soil is neither excessively acid nor strongly alkaline, in which case the clue to disappointing yields or performance may lie in poor soil manage­ment. You won’t need gadgets, merely an observant eye, to be aware of this state of affairs: little new growth, stunted and yellowing leaves, smaller and fewer flowers, and reduced crops. Provided that soil acid­ity – and drainage – is not the problem, a dose of a general fertiliser will generally put things right.

What is pH scale

Acidity and alkalinity are measured against the pH scale – the letters stand for ‘potential of Hydrogen’. The full scale runs from 1 to 14, but most garden soils are within the range 4.5-8.0. The neutral point on the scale is 7. Readings below this denote acid soil, above means alkaline. The majority of plants thrive in slightly acid soil (pH 6.5) though there are exceptions. Most vegetables, for example, do best on slightly alkaline soil (pH 7.5).

Soil Testing kits

To establish the soil’s acidity and conse­quently the types of plants it will support, you can use an inexpensive soil-testing kit, readily available from garden centres and shops. Such kits are easy to use: small soil samples are shaken with a chemical such as barium sulphate which stabilises the sus­pended soil while an indicator dye changes colour depending on the level of acidity around it. The result is compared with a colour-coded chart to give an approximate indication of the soil acidity. From the read­ing, you can assess what needs doing, if anything. Lime is used to bring an acid soil to near the neutral point; it is more difficult to turn an alkaline soil into an acid one.

Electronic pH meters, fitted with a probe for pushing into the soil, give instant read­ings, but are more expensive. They don’t necessarily give better information than the simple soil-testing kits, and the same money might be better spent on a fertility meter. This will tell you the level and concentration of major plant foods in the soil – nitrogen, phosphorus and potassium – and help you to decide on the most appropriate fertiliser treatment.