Measuring the pH in the soil

Nutrients can exist in the soil as dissolved salt compounds, enabling plants to absorb them easily. But depending on the pH, individual main and micronutrients can bind to soil particles. If the pH is sub-optimal, then it is possible that although the soil contains an abundant supply of all the nutrients, the plants cannot absorb them.
It is reasonable to suspect this if you only have stunted or deformed plants after fertilising extensively. If the soil pH is too low, plants will not have enough nitrogen, potassium and calcium, for example. On the other hand, if the pH is too high, then the supply of these same nutrients is abundant but iron, manganese or boron are lacking.
However, the excessive availability of certain nutrients can also be problematic for your plants in extreme cases. Large quantities of aluminium are available to plants in soils that are high in acidity, for example. You may already be familiar with this effect in a scaled down form from the blue colouring of French hydrangeas that grow in acidic soils containing aluminium. But too much aluminium poses a health threat, which means that hardly any garden plants will survive in the long term.

By ensuring that the soil pH is balanced, you are helping your soil to help itself. Only then can it provide the plants with all the nutrients available. As you can see from our table, extremes are never healthy for ultimately there's always an undersupply or oversupply of individual main and micronutrients.

The activity of soil organisms is also dependent on the pH. In acidic soil with a low pH, soil organism activity is extremely low. To better understand the consequences of this in the garden, let's take a brief look at the tasks of our small soil helpers in four steps:

1. The first step sees larger soil organisms like earthworms convert organic substances in the soil (e.g. leaves and sticks) into valuable humus. Much smaller microorganisms then decompose this and nutrients such as nitrogen are produced, which are then available to plants. 
2. The two (the larger soil organisms and the smaller microorganisms) thus combine to form a kind of recycling chain. The structure of the soil is effected if the soil organisms are no longer active, i.e. it isn't as fine and crumbly and leaves or sticks are not decomposed and converted into humus.
3. This in turn effects the microorganisms, which do not find enough humus for processing (mineralisation).
4. At the end of the chain, the plants in your garden soil also lack the very minerals that are organically bonded, i.e. only released by the activity of the microorganisms. These include primarily nitrogen, but also potassium and phosphorus.

The soil is said to be alkaline (or basic) when the pH is more than 7.5. Alkaline means that the soil contains a lot of lime. Hardly any plants can tolerate extreme levels of pH (about 9). Such an unusually high pH in the soil can also be caused by very frequent liming or many years of watering with calcareous (hard) water.

• Nutrients such as iron, manganese, copper, zinc and boron are only available to plants in small quantities, which can lead to stunted growth and deformed plant parts.
• At the same time, soil life is stimulated – earthworms and microorganisms are especially active, causing organic soil material to decompose into humus and in turn humus into minerals to such an extent that the soil structure suffers as a result. The soil has hardly any structure left to absorb water or air.
• On the other hand, the active work of the soil organisms leads to an oversupply of nitrogen, potassium and phosphorus in the soil – all substances that were previously organically bonded and are now released through the decomposition processes.

As a rule, you don't need an overly accurate result to determine which way you need to go with your garden soil. That's why simple self-tests at home are usually sufficient. You can use test strips similar to those used in swimming pools or liquids that – depending on reading – turn a different colour. You could consider buying a special measuring device if you want to take measurements frequently and easily.
On the other hand, you can also have a soil sample analysed if you want more precise information. The advantage here is that since the measurement is extremely accurate, precise conclusions can be drawn about which plants will grow particularly well in your soil. Such soil analyses also deliver information about the concentration of other nutrients in the soil, so you can establish whether an entirely different problem may prevail.