Determine the pH of the soil

Soil pH is a critical factor in plant growth - many gardeners know this. We simply explain to you what the soil pH has to do with acidic soil and alkaline soil and how they influence the degree of acidity.

The pH value of the soil shows with a single number whether a soil is more acidic, neutral or alkaline. The letters pH stand for potentia Hydrogenii, which translated from Latin means “potential / power of hydrogen” and denotes the content and activity of hydrogen in the soil. The more hydrogen there is in the soil, the more acidic it is and the lower the measured soil pH value.
But of what interest is the pH value of the soil or even the content of hydrogen ions for a gardener?
The pH value influences a number of chemical and biological processes in the soil. The availability of nutrients, the activity of the soil, the structure of the crumbs, and thus also the plant growth, depend on the acidity of the soil. It is not for nothing that one can find an optimal soil pH value for all crops at which they can grow as best as possible.

Tip: Central European soils most often have a weakly acidic pH value of 5.5 to 6.5 and this range is also optimal for a very large part of our useful and ornamental plants. Exotic or very special plants, however, may need a more acidic or more basic soil. In addition, there are many areas in Central Europe whose soil acidity deviates significantly from this standard. So it is worth looking into the pH value of your own soil - with the aim of supporting plant growth in the garden as much as possible.

Determine the pH of the soil

If you have just bought a garden or a piece of land, it is very interesting to find out what the pH value of the soil is. Because based on this value, you can make a well-founded decision as to which plants will grow well here or whether the degree of acidity should perhaps even be changed.

tip: For many garden owners, the lawn in particular is an important component of the garden. The suitable pH value for lawns is between 5.5 and 7.5, depending on the type of soil. Often there are problems with moss, other weeds or simply poor lawn growth due to a different acidity. So if you check in advance what acidity your own soil has, you can save yourself a lot of frustration. The soil under existing lawns can also be improved by using the Liming the lawn.

There are several methods of assessing the pH of the soil. These are quite easy to use for garden owners:

pH soil test

There is a whole range of different floor testers that you can use: For example, they are simple and rather imprecise pH soil tests with indicator paper or special test kits that display the pH value via the color change of a liquid, available. There are also digital pH value measuring devices through to highly professional laboratory tests that, in addition to the pH value of the soil and the nutrient content, also measure the Determine soil type.
The fact is that the test method used affects what result you get. Simple tests use water or distilled water to measure pH; laboratories usually use calcium chloride suspensions. Digital measuring devices even measure directly in the ground by measuring the current flowing between two measuring electrodes and interpreting it as a pH value.
The measurements from specialized laboratories are the most reliable and most comparable. All other methods can only be regarded as approximations, which, however, are usually completely sufficient in the hobby garden area.

Tip: When you do a pH test of your soil yourself with a test kit or indicator strip make sure that you use distilled water and that the suspension is as warm as 25 ° C is. Because the measured pH value is influenced by the temperature and substances dissolved in the water.

Pointer plants for the pH of the soil

As mentioned above, plants always prefer a certain pH value range. In a soil that is much too acidic or alkaline, they perish or do not germinate in the first place, while at the right pH values ​​they thrive or even reproduce abundantly.
The positive side effect is that some wild plants or weeds can be used as indicators, ie “indicators”, for soil properties. Good indicator plants (“bio-indicators”) are of course only those genera and species that have specialized in a narrow pH range. Common plants such as the dandelion (Taraxacum sect. Ruderalia) or the Chickweed (Stellaria media), which seem to grow everywhere, are therefore not good indicator plants because they tolerate a wide variety of conditions.
If you see one of these plants growing healthy and in large numbers in your garden, you can roughly estimate whether your soil is acidic or basic:

Bio-indicators for acidic soils	Bio-indicators for basic soils
Yellow clover (Medicago pupulina) Hasenklee (Trifolium arvense) Little sorrel (Rumex acetosella) Little Wiesenknopf (Sanguisorba minor) Cornflower (Centaurea cyanus) Creeping cinquefoil (Potentilla reptans) Marsh valerian (Valeriana dioica) Wild pansy (Viola tricolor)	Field mustard (Sinapsis arvensis) Field barbarian (Consolida regalis) Hyssop (Hyssopus offcinalis)

What does the pH of my soil mean?

If the pH value of the soil is measured, you basically get a measure of how much hydrogen there is in the soil and how active it is. Depending on the amount of hydrogen in relation to the oxygen in the soil, find There are different compounds of these two elements in the soil solution: in particular oxonium ions (H₃O⁺), Water (H₂O) and hydroxide ions (OH^–) are always present, but can be found in different amounts depending on the acidity of the soil.

Acid soil	Neutral ground	Basic soil
PH value	3 – 6,5	7	7,5 – 9
Occurrence of hydrogen (H +)	Hydrogen is mainly considered H3O + (Oxonium) found in the soil.	Hydrogen is mainly considered H2O (water) found in the soil.	Hydrogen is mainly as OH- (Hydroxide) found in the soil.
Ratio of hydrogen to oxygen	3:1	2:1	1:1

So an acidic soil contains a lot of oxonium, a neutral soil mainly contains neutral water and an alkaline soil contains a lot of hydroxide.
Ultimately, it is the presence of these three compounds that creates the effects on the soil. They indirectly influence, for example, the availability of nutrients, the activity of soil organisms and the degree of humus formation.

Acid soil (pH <5.5)

In acidic soils, in which a lot of reactive oxonium can be found, nutrients are otherwise difficult to obtain dissolved, salts and minerals decomposed and with that some trace nutrients like iron, manganese and zinc are better available. However, if the acid is too strong, substances can also be released that harm most plants - such as aluminum. Fungi and fungal microorganisms feel very comfortable in more acidic soils, while numerous soil bacteria cannot survive. This has an impact on the humus-forming processes in the soil: On acidic soils, the fungi in the soil create a lighter, less high-quality humus with a reddish color.

Why does the soil get acidic?

Acid soils arise when the minerals in the soil undergo the constantly acidifying effect of slightly acidic rainwater, Do not compensate for rotting organic material, acidic fertilizers and hydrogen-secreting plant roots can. One speaks of the so-called buffer capacity of the soil. Sandy soils, for example, are less “buffered” than clay soils and can therefore be faster and stronger acidify - this can be observed, for example, in the moor, a purely organic soil without Rock proportions. Here no rocks such as limestone buffer the acidification and so the moor becomes more and more acidic. Incidentally, water saturation and waterlogging also lead to acidity in the soil, because carbon dioxide from the air reacts in the absence of oxygen to carbon dioxide - this is another reason why the very wet moors are particularly acidic are.

Which plants grow in acidic soil?

Only a few specialists are adapted to (very) acidic soils, such as bog plants such as hydrangeas (Hydrangea), Rhododendrons and azaleas (rhododendron), Blueberries (Vaccinium), Lavender heather (Pieris), Pagans (Calluna, Erica), many sweet grasses (Poaceae), Skimmien (Skimmia) and splendid bells (Enkianthus campanulatus).

Alkaline soil (pH> 7)

Bacterial soil organisms feel more comfortable in basic soils, in which more hydroxide can be found, than in acidic soils. This in turn means that many organically stored nutrients such as nitrogen, phosphates and potassium are more readily available at high pH values ​​because the soil organisms release them. The soil structure often improves as the soil pH value rises, making the soil more crumbly and looser. In extremely alkaline soils, however, important trace elements are hardly available, so that plant growth is hindered again and fertility decreases.

Why does the soil become alkaline?

Alkaline soils arise when a soil develops on a rock that is very lime-rich, classically on limestone. Even soils with a high clay or silicate content can (over) compensate for released hydrogen again and again, so that there is relatively little Oxonium in the soil solution. A good example are the very fertile black and brown soils of the Hildesheimer Börde, whose high pH value results from the high proportion of loess in the mineral content of the soil.

Which plants grow in alkaline soil?

Few plants grow particularly well on basic soils. Some cacti and succulents prefer a neutral to slightly alkaline soil, as do mountain plants such as the pasque flower (Pulsatilla), Everlasting flowers (Helichrysum), but also garden plants such as bulbous (Allium), Black salsify (Scorzonera) and lavender (Lavandula) love high pH levels.

Weakly acidic or neutral soil (pH 5.5 - 7)

In the golden mean, i.e. in weakly acidic, weakly alkaline or neutral soil, the soil structure is good and all nutrients are sufficiently available. No wonder most plants prefer this state. Anyone who owns a weakly acidic or neutral soil usually no longer has to work with lime or other agents, but can start fertilizing and planting straight away. A large part of the soils in Germany is slightly acidic and a large part of our native plants is adapted to it.

Why is the soil weakly acidic or neutral?

Soils with a balanced degree of acidity are able to buffer acidifying influences by using Clay minerals and metal oxides (such as iron oxide) neutralize hydrogen and thus the pH value is always between 5 and 8 hold. Small amounts of limestone are also often present. In addition, humus acts as a buffer and stabilizes the pH value. Loamy, humus soils on limestone, as they often occur in Germany, are often slightly acidic to neutral.

Which plants grow in weakly acidic or neutral soil?

Most crops and ornamental plants prefer a medium acidity. Only specialists (bog plants, desert plants, tropical plants, ...) from distant countries or those who are adapted to very special conditions, do not do well on weakly acidic to neutral soils survive.

Tip: with the floor instead of against the floor
When the soil in your own garden is not just slightly acidic or neutral, but rather in an extreme area moves, you have two options: First, you can try to seal the soil by adding appropriate additives change. Changing the pH of large areas often costs a lot of money, especially when the pH is extremely acidic or alkaline. In addition, the change is sometimes not permanent, but the soil returns to its individual pH value through the soil-forming materials. Second, if you have a strongly acidic or alkaline soil, you can simply consider adding specialized plants who love these conditions - and other plants, for example in pots or raised beds with high-quality potting soil such as our Plantura organic soil to plant.

Change the pH of the soil

Is your soil slightly too acidic or too alkaline for your purposes, or has it got out of balance due to years of management errors? If you want to change the pH value of your soil permanently, you should check the pH value annually and can do the following to change the value.

Soil too acidic

A soil that is slightly too acidic, for example with a pH value of 5, can easily be corrected with lime. Which type of lime should be used, however, depends on the type of soil: Sandy soils, for example, are easier to influence than clay-rich soils. The humus content also has an influence on the correct form and quantity of lime. As a rule, the amount of lime is divided into two doses, so it is limed two years in a row. Carbonate of lime is well suited for sandy and peaty soils. Quicklime works very quickly, is even corrosive and helps even heavy, clayey soils to achieve a higher pH value. Only a soil pH test can tell you how much lime needs to be distributed. Tests for the hobby area also often contain good information on how to proceed. Another way to increase the pH of the soil is to regularly use basic bed rock made from diabase and other types of basalt.

Soil too alkaline

Acidifying a soil is a little more difficult than making it more alkaline. The cause of a soil that is too alkaline is the rocks that form it, and so the lowering of the pH value quickly turns into a battle against windmills, which has to be carried out every year. Soils can be acidified with elemental sulfur, which is also available as so-called sulfur flowers or sulfur flowers, because this is converted into sulfuric acid by bacteria in the soil. The dosage requires a sure instinct: 50 to 100 g of sulfur flowers per square meter can lower the pH value of a medium-heavy soil by more than one unit. Light soils react more sensitively and become more acidic, heavy soils, especially very humus-rich soils and compost soils react much more slowly and require larger quantities of the sulfur flowers to become acidic will. Natural ways to acidify the soil are the use of grape marc, acidic primary rock flour made from granite, and regular mulching. If you want to save peat in the garden, but don't want to do without it entirely, you can also use plants on a regular basis Pour peat extracts: Two handfuls of peat are poured into a 10 liter watering can for a week inserted. Then the peat is removed or strained and the now acidic irrigation water is given to the acid-loving plants. The effect of this treatment is not permanent and has to be repeated monthly.

The pH of the soil is closely related to the type of soil. In our special article we explain how you can use the Determine soil type can.