Soil pH is a crucial factor for plant growth - as many gardeners know. We'll explain to you simply what soil pH has to do with acidic soil and alkaline soil and how you influence acidity.
Soil pH is a single number that tells you whether a soil is acidic, neutral or alkaline. The letters pH stand for potentia Hydrogenii, which translated from Latin means "potential/power of hydrogen" and describes 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?
PH affects a number of chemical and biological processes in the soil. Nutrient availability, activity of soil life, crumb structure and thus directly 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 crop plants, in which they can grow in the best possible way.
Tip: Central European soils most often have a slightly acidic pH value of 5.5 to 6.5 and this range is also relevant for a very large part of our useful and Ornamental plants optimal. However, exotic or very special plants may require a more acidic or more basic soil. There are also many areas in Central Europe whose soil acidity deviates greatly from this standard. So it's worth checking the pH of your own soil - with the aim of supporting plant growth in the garden as best you can.
Determine pH of soil
Especially when you have just bought a garden or a piece of field, it is very interesting to find out what the pH value of the soil is. Because you can use this value to 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 is an important part of the garden. The appropriate pH for lawns is between 5.5 and 7.5, depending on the type of soil. There are often problems with moss, other weeds or simply poor lawn growth due to a deviating acidity. So if you check the acidity of your own soil in advance, you can save yourself a lot of frustration. The soil under existing lawns can also be improved in this way by liming the lawn.
There are several methods to estimate soil pH. These are quite easy to apply for garden owners:
pH soil test
There is a whole range of different soil testers that you can use: For example, 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 are available . There are also digital pH meters and highly professional laboratory tests that determine not only the pH of the soil and the nutrient levels, but also the type of soil.
The fact is that the test method used affects the result you get. Simple tests use water or distilled water to measure pH, laboratories typically use calcium chloride suspensions. Digital measuring devices even measure directly in the soil by measuring the current flowing between two measuring electrodes and interpreting it as a pH value.
Measurements from specialized laboratories are the most reliable and comparable. All other methods can only be considered as approximations, although they are usually completely sufficient for hobby gardening.
Tip: If you want to carry out a pH test of your soil yourself with a test kit or an indicator strip, make sure that you use distilled water and the suspension if possible 25 °C warm. Because the measured pH value is influenced by the temperature and the substances dissolved in the water.
Indicator plants for soil pH
As mentioned above, plants always prefer a certain pH range. If the soil is much too acidic or basic, they will die or will not germinate at all, while with the right pH values they will thrive or even multiply profusely.
The positiveA side effect is that you can use some wild plants or weeds as an indicator, i.e. "indicator", for soil properties. Good indicator plants ("bio-indicators") are of course only the genera and species that have specialized in a narrow pH range. Common plants such as dandelion (Taraxacum sect. Ruderalia) or chickweed (Stellaria media), which They seem to grow everywhere so they are not good indicator plants as they tolerate a wide variety of conditions.
Seeing any of these plants growing he althy and in large numbers in your garden can give you a rough idea of whether your soil is acidic or alkaline :
| Bio-Indicators for Acid Soil | Basic Soil Biological Indicators |
| Yellow Clover (Medicago pupulina) Hare Clover (Trifolium arvense) Lesser Sorrel ( Rumex acetosella) Small burnet ( Sanguisorba minor) Cornflower ( Centaurea cyanus ) Creeping cinquefoil ( Potentilla reptans) Marsh valerian ( Valeriana dioica) Wild pansy ( Viola tricolor) | Mustard (Sinapsis arvensis) Larkspur (Consolida regalis) Hyssop ( Hyssopus offcinalis) |
What does my soil pH mean?
Measuring soil pH is basically giving you a measure of how much hydrogen is in the soil and how active it is. Depending on the amount of hydrogen in relation to oxygen in the soil, different compounds of these two elements are found in the soil solution: Oxonium ions in particular (H3 O+), water (H2O) and hydroxide ions (O H-) are always present, but are found in varying 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 found in soil as H3O+ (oxonium). | Hydrogen is mainly found as H2O (water) in soil. | Hydrogen is mainly found as OH-(hydroxide) imto find ground. |
| Ratio of hydrogen to oxygen | 3:1 | 2:1 | 1:1 |
So acidic soil is high in oxonium, neutral soil is high in neutral water, and alkaline soil is high in 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 level of humus formation.
Acid soil (pH <5,5)
On acidic soils, in which there is a lot of reactive oxonium, nutrients that are otherwise difficult to access are dissolved, s alts and minerals are decomposed and some trace nutrients such as iron, manganese and zinc are more readily available. However, if the acid is too strong, substances can also be released that damage most plants - such as aluminum. Fungi and fungal microorganisms thrive in rather acidic soils, while numerous soil bacteria cannot survive. This has an impact on the humus-forming processes in the soil: on acidic soil, the fungi in the soil produce a lighter, reddish-colored humus of lower quality.
Why is the soil getting acidic?
Acid soils develop when the minerals in the soil cannot offset the constant acidifying effects of slightly acidic rainwater, decaying organic matter, acidic fertilizers, and hydrogen-secreting plant roots. One speaks of the so-called buffer capacity of the soil. Sandy soils, for example, are less well "buffered" than clay soils and can therefore acidify faster and more intensely - this can be observed, for example, in moors, a purely organic soil without rock content. Here no rocks like limestone buffer the acidification and so the moor becomes more and more acidic. Incidentally, water saturation and waterlogging also lead to acid in the soil, because carbon dioxide from the air reacts to carbonic acid in the absence of oxygen - this is also a reason why the very wet moors are particularly acidic.
What plants grow in acidic soil?
Only a few specialists are adapted to (very) acidic soils, such as ericaceous plants such as hydrangeas (Hydrangea), rhododendrons and azaleas (Rhododendron ), blueberries (Vaccinium), lavender heathers (Pieris), heathers (Calluna, Erica), many grasses (Poaceae), Skimmia (Skimmia) andBluebell (Enkianthus campanulatus).
Alkaline soil (pH> 7)
Bacterial soil organisms thrive in alkaline soils, where more hydroxide is 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 a result of an increasing soil pH value, the soil becomes more crumbly and loose. On extremely alkaline soils, however, important trace nutrients are hardly available, so that plant growth is hindered again and fertility decreases.
Why is the soil becoming alkaline?
Alkaline soils are formed when a soil develops on a very calcareous rock, classically limestone. Even soils with a high clay or silicate content can repeatedly (over)compensate for released hydrogen, so that there is only a small proportion of oxonium in the soil solution. A good example is the very fertile black soil and brown soil of the Hildesheimer Börde, whose high pH value results from the high proportion of loess in the mineral content of the soil.
What plants grow in alkaline soil?
Few plants grow particularly well in basic soil. Some cacti and succulents prefer a neutral to slightly alkaline soil, as well as mountain plants such as Pasque Flower (Pulsatilla), Helichrysum (Helichrysum), but also garden plants such as Bulbous (Allium), salsify (Scorzonera) and lavender (Lavandula) love high pH levels.
Slightly acidic or neutral soil (pH 5.5 - 7)
In the golden mean, i.e. in slightly acidic, slightly alkaline or neutral soil, the soil structure is good and all nutrients are sufficiently available. No wonder most plants prefer such a state. If you own slightly acidic or neutral soil, you usually no longer have to work with lime or other agents, but can start fertilizing and planting directly. A large part of the soil in Germany is slightly acidic and a large part of our native plants are also adapted to it.
Why is the soil slightly acidic or neutral?
Bottoms with abalanced acidity are able to buffer acidifying influences by neutralizing hydrogen with clay minerals and metal oxides (such as iron oxide) and thus always keeping the pH between 5 and 8. Even small amounts of limestone are often present. In addition, humus acts as a buffer and stabilizes the pH value. Loamy, humus-rich soils on limestone, as they often occur in Germany, are often slightly acidic to neutral.
Which plants grow in slightly acidic or neutral soil?
Most cultivated and ornamental plants prefer medium acidity. Only specialists (moorbed plants, desert plants, tropical plants,… ) from distant countries or those that are adapted to very special conditions cannot survive well on weakly acidic to neutral soils.
Tip: With the ground instead of against the ground
If the soil in your own garden is not just slightly acidic or neutral, but rather in an extreme range moves, you have two options: First, you can try to change the soil by adding appropriate additives. Changing the pH of large areas is often expensive, 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. Secondly, if you have a highly acidic or alkaline soil, you can consider simply choosing specialized plants that love these conditions - and planting other plants, for example in containers or raised beds with high-quality potting soil such as our Plantura organic soil.
Change soil pH
Is your soil slightly too acidic or too alkaline for your purposes, or has it been out of balance due to years of management errors? If you want to permanently change the pH of your soil, you should check the pH on an annual basis and you can do the following to change the value.
Soil too acidic
Soil that is slightly too acidic, for example with a pH value of 5, can easily be corrected with lime. However, the type of lime that should be used depends on the type of soil: sandy soils, for example, are easier to influence than soils rich in clay. The humus content also has oneInfluence on the correct form and amount of lime. As a rule, the application of lime is divided into two doses, i.e. lime is applied for two years in a row. Carbonate of lime is well suited to sandy and peaty soils. Quicklime works very quickly, is even caustic and helps to increase the pH value even in heavy, clayey soils. Only a soil pH test can tell you how much lime needs to be distributed. Tests for the hobby area often contain good information on how to proceed. Another way to increase the pH value of the soil is to regularly use basic rock flour from diabase and other types of bas alt.
Soil too alkaline
Acidifying soil is a little more difficult than making it more alkaline. The reason for soil that is too alkaline is the rocks that form it, so lowering the pH value quickly becomes a battle against windmills that has to be carried out every year. Soils can be acidified with elemental sulphur, which is also available as so-called sulfur flower or sulfur flower, because this is converted into sulfuric acid by bacteria in the soil. Dosing requires a delicate touch: as little as 50 to 100 g of flower of sulfur 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 acidic more easily, heavy, especially very humus-rich soils and compost react much more slowly and require larger amounts of sulfur flower to become acidic. Natural ways to acidify the soil are the use of grape pomace, acidic granite bedrock and regular mulching. If you want to save peat in the garden, but don't want to do without it completely, you can also water your plants regularly with peat extracts: To do this, two handfuls of peat are placed in a 10-liter watering can for a week. The peat is then removed or strained and the now acidic irrigation water given to the acid-loving plants. However, the effect of this treatment is not permanent and must be repeated monthly.
Soil pH is closely related to soil type. In our special article we explain how you can determine the type of soil in your garden.