If you analyze your garden soil correctly and improve it in a targeted manner, you can be sure of gardener’s happiness! In this article, we will show you how to correctly determine your garden soil with the soil analysis, help you with the interpretation of the soil analysis and give you practical assistance to improve your garden soil.
To be successful in the garden, you need to know your soil. Then you will know in advance which plants will do well in your garden and which are not worth planting. You also save money if you fertilize less, but more specifically. Soil composition, pH and nutrient content are key parameters in soil analysis. We’ll show you how to find them.
Determine the type of soil in the self-test
For the first analysis you only need your hands, with which you feel the type of floor. To do this, pick up some soil from a bed. Work the earth with your hands. Decide which of the three types described below it most closely matches:
- Light soil: If the soil does not stick together while kneading but trickles through between your fingers, then it is a light soil, which consists largely of sand. This can also be seen from the grains that you can feel when rubbing between your fingers. Sandy soils are easy to work with with a spade and digging fork. They contain a lot of air and can warm up quickly in spring. However, their ability to store water and nutrients is poor.
- Heavy soil: roll the earth between your palms. If it feels a little fat and it results in easily malleable sausages, the bottom contains a lot of clay. This is great at storing water and nutrients. The other side of the coin: clay soil often leaves little air to the roots, compacts quickly and is difficult to process.
- If the earth can be shaped, but cracks appear, it is a type of soil that lies between clay and sandy soils. As always with the golden mean, it is ideal for most plants because the water, air and nutrients are in a balanced ratio.
There are of course all kinds of transitions between these three types of soil. In addition, the finger test says nothing about the content of organic matter, which is of great importance for the structure and fertility of the soil. If you want to know more about it, you can start experiment number two: the slurry sample.
Soil analysis with the slurry sample
For a slurry sample, you need a larger glass, ideally with a screw cap and a wide opening, a tablespoon and some water. Fill the jars with garden soil and water and shake them vigorously.
Although the result looks rather cloudy at first glance, it gives you more clarity about your soil type. This is because slurrying in water separates the different parts of the earth.
Depending on their size and weight, the particles sink at different speeds and are deposited in layers at the bottom of the glass. Some also swim to the surface of the water. Depending on the thickness of the layers, you can see the relationship between the components.
- Coarser grains of sand are deposited in the bottom layer after just a few minutes
- Fine clay particles remain in the solution for a long time
- Clay tends to give the water a reddish color
- Humus colors the water almost black (the darker the water, the more humus in the soil)
- Undecomposed parts of plants float on top of the sludge sample
Step 1: slurry sample: fill in soil sample
The mud sample: Fill a screw jar about a quarter full with fresh garden soil.
Step 2: fill up with water
Pour tap water into the glass to about 1 cm below the rim.
Step 3: shake the sample
Unscrew the lid and shake the jar vigorously.
Step 4: Evaluation of the soil sample
Evaluation: After 15-30 minutes you will have the result: If the formation is difficult (left), the clay particles remain suspended for a long time and color the water cloudy. In light soils (right), the sand particles settle quickly. The dark color of the water indicates the humus content. Plant remains float above. The clay floor (middle) is optically in between.
How to measure the pH in the soil
With a pH self-test from the garden center (e.g. Neudorff) you can quickly find out whether the soil is acidic or basic. This is how it works: Take the soil sample from the correct soil layer (5 to 10 cm depth for lawns, 20 to 30 cm in the vegetable garden). Put some of the soil in the glass tube and pour distilled water on it. Now add the tablet and shake the closed tube until it dissolves. Once the sediments have settled, the result is determined by comparing the color of the liquid with the color scale on the package.
Have a professional soil analysis done
With a professional soil analysis from the laboratory, you will get a good insight into the current nutrient and mineral content of your soil. This investment pays for itself quickly: In addition to the current nutrient content, you will receive a fertilizer recommendation. Often you save money the next time you fertilize, because often the supply of phosphate or potassium in the soil is already completely sufficient. You will use the information from the soil analysis for the next five to six years. Only then is a new examination due.
Take the soil sample correctly
Whether vegetable or strawberry beds, berry bushes, lawns, orchards, cold frames, ornamental gardens or conifers: you need a separate sample for each garden area that you want to have analyzed. This should consist of at least ten punctures distributed as evenly as possible over the area in question, which you mix well with one another. The more punctures you make, the more accurate the result will be. Take the samples very carefully – this is where the greatest source of error lurks.
On request, you will also receive detailed information on taking samples from the analysis laboratory. Take sufficient soil material (usually at least 300g) from the well-mixed soil sample and put it in a well-sealable bag. Don’t forget: Always label the soil sample precisely with the location of the sample and the date.
Take soil sample
Step 1: the first stitch
The depth of the soil sample depends on the roots of the crops. A sample of the upper 10cm is sufficient for lawns, 20cm for other crops and up to 30cm for vegetables. If you pull the sample with a spade, proceed in two steps: dig a pit at the required depth for the so-called first cut. They put the excavation next to the pit. Pay attention to straight walls that are as vertical as possible.
Step 2: the second stitch
The second pass is crucial: it provides the material for the soil sample to be sent. Use your spade to dig a thin layer of earth out of the pit wall. Then cut away most of the soil on both sides of the sample so that only a 2 cm narrow strip that runs from top to bottom remains. Mix this well with at least nine other such samples in a bucket.
Step 3: taking samples with the boring stick
Sampling is easier with a special drill stick. Press the tool 10 or 20-30cm deep into the ground.
Then it is rotated so that the groove in the metal rod is filled with soil. Pull out the burr and put the sample in a bucket. Repeat this at least nine times.
When do you do a soil analysis?
Our recommendation: send in your samples for examination in November! In theory, you could wait until spring to do this. But then the laboratories have high season. In late autumn, on the other hand, the soil is neither freshly fertilized nor does the nutrient content change significantly over the winter. And you will get your results quickly and you can plan the next fertilization phase in peace. However, if you should send in your soil sample in the summer, plan in any case 3 to 4 weeks until you get your results from the laboratory.
What different soil analyzes are there?
In almost all soil analyzes, the nutrient content of the soil is primarily determined. It tests how high the proportion of organic carbon is, because this shows how rich in humus a soil is. The supply of phosphorus and potassium is also checked. In addition to the general soil analyzes, there are also special analyzes that are specifically tailored to a specific purpose. In a turf soil analysis, the molybdenum and nitrogen content is also determined.
Special case nitrogen: Nitrogen is not recorded in most analyzes for house gardens. Its content changes constantly depending on temperature, humidity and aeration of the soil as well as leaching after rain. In particular, the content of mineralized nitrogen (this is easily absorbed by plants) can only be determined approximately in a soil analysis, as it evaporates quickly. If the analysis cannot be carried out immediately after taking the sample, the sample must be cooled and sent to the laboratory as moist as possible.
In addition to the nutrient content, you can also have the soil tested for pollutants. This is interesting for vegetable gardens and families with young children who can easily pick up soil particles. Pollutants are not only a problem in former industrial sites or mining areas – heavy metals can also accumulate in the soil near roads. The laboratory tests for heavy metals that are readily available to plants and can accumulate in them. Such analysis tests are also available for bodies of water or contaminated sites. You will find a comprehensive range of different soil analyzes e.g. at the soil analysis center.
Interpreting the results of the soil analysis correctly
pH value: The pH value indicates whether a soil reacts neutral (pH value around 7), acidic (less than 7) or more basic (above 7). Garden soil should have a pH between 5.5 and 7.2. Depending on the composition (sand, loam or clay), every soil always has a specific, ideal pH value:
- Sandy soil: 5.3-5.7
- Sandy loam: 6.3–6.7
- clayey loam: 6.9
- Bog soil: 3.8-4.3
If the soil is too acidic or basic (for example sandy loam with a pH value below 6), nutrients are more difficult to absorb by the plants. This can lead to deficiency symptoms despite sufficient nutrients in the soil.
Organic carbon (C org.) / Humus content: Organically bound carbon (C org.) Can be found in soil organisms, dead plants and animals and in humus. Conclusions about the humus content, fertility and nutrient availability can be drawn from the amount of organic carbon in the soil. If the proportion of organic carbon in the soil is very high, there is a good basis for a sufficient supply of nutrients.
C / N ratio: In order to ensure a good supply of nutrients, the ratio of organic carbon to nitrogen must be correct. The ratio of carbon to nitrogen (C / N) should be in the ratio of 8/1 to a maximum of 20/1.
Phosphorus content (P2O5): Phosphorus is an essential component for plants and is required for many different functions. Among other things, phosphorus plays a major role in DNA, energy balance and as a messenger substance. A lack of phosphate limits plant growth and the plants then react with increased root growth.
Potassium (K2O): Potassium is also an essential element that organisms need for metabolism. A lack of potassium leads to growth disorders and necrosis on the leaf margins. Caution: too high a potassium concentration damages plants, since an oversupply of potassium reduces the absorption of e.g. B. prevents magnesium and calcium. In Germany there is usually sufficient potassium in garden soils. Therefore, maintenance fertilization should only be used to top up the amount of potassium that is lost through the harvest.
Magnesium (MgO): The magnesium content is highly dependent on the geological source material, with sandy soils usually containing little magnesium. Characteristic of a magnesium deficiency are lightening of the oldest leaves and leaves dying from the leaf tip. However, the absorption of magnesium can be reduced by an oversupply of other minerals such as potassium, calcium and manganese.
Trace elements such as boron, copper, manganese, iron, zinc and molybdenum play a major role in plant development, but are only required in very small quantities. It should only be re-fertilized if there is a specific deficiency, because the oversupply often also has negative effects on the plants.
Special case iron: Iron is important for the build-up of chlorophyll and the formation of carbohydrates and proteins. Iron is usually sufficiently available in the soil, and a deficiency often only arises from a reduced availability. This can be triggered on the one hand by a pH value that is too high or by a too high concentration of calcium and magnesium carbonate-rich soils. Usually, however, the use of hard irrigation water (lime-containing tap water), which inhibits the absorption of iron, is responsible for an iron deficiency. This can be prevented by using only softened water (preferably rainwater). Acute deficiency can be remedied by giving iron in the form of Fe-EDDHA (a cheleat).
Pollutants such as lead, cadmium, chromium, nickel and mercury are among the toxic heavy metals and cause metabolic disorders in humans and animals. Plants partially absorb heavy metals; this is relevant when they are consumed. A concrete analysis of the soil for the pollutant found can provide more precise information about the content.
Pollutants in the soil – what now?
If a pollutant load has been found in the soil, there are a few tricks to keep the absorption of the pollutants as low as possible. It starts with choosing suitable plants. Not all vegetable plants absorb pollutants equally well: strawberries and radishes, for example, are known to have a particularly high concentration of lead. Tomatoes and zucchini, on the other hand, are less polluted.
Proper soil care also plays a role: a pH value of 7 and a sufficiently high humus content reduce the absorption of heavy metals by plants. Plant parts, roots and leaves close to the ground should be washed or removed thoroughly before consumption. If you also cover the soil with straw or mulch, you prevent soil particles from being deposited on the plants. In the vicinity of roads, polytunnels protect against pollutants from air and precipitation.
Tip: Leaf and root vegetables accumulate many pollutants such as lead and cadmium. In tree and bush fruit, the pollution is usually hardly measurable. So, instead of kohlrabi and carrots, plant grapes or sour cherries.
Improving the garden soil: how to proceed in a targeted manner
- The soil is too acidic: If the pH value is too low, you can increase it with mixed or garden lime.
- The soil is too alkaline: If the pH value is too high, it can be reduced with acidic fertilizer made from coniferous compost. The pH value can also be lowered with humus soil.
- Ideal pH value: Once the soil has reached the ideal pH value, maintenance liming should be carried out every two years. This counteracts the natural acidification of the soil. The right time to lime the lawn is spring and autumn: if you rake in garden lime on the surface, it will open up somewhat by the following spring.
Change the soil composition
- Sandy soil: In light and sandy soils, clay minerals such as betonite help to increase the storage capacity of water and nutrients. For this purpose, 100 to a maximum of 300 g / m2 are recommended.
- Clay soil: So that clay soil becomes loose and permeable, you add coarse rock flour and sand. They ensure better ventilation and make the soil more permeable for water and of course for the plant roots.
Correct procedure for nutrient deficiency
Once the nutritional status of the garden soil has been determined, the soil can be supplied with the missing nutrients and trace elements. Complete fertilizer is unsuitable for this, because it covers all nutrients and thus quickly leads to over-fertilization – with negative effects on plants and soil water. It is better to use special fertilizers that only contain the missing substances.
Fertilize correctly: How much and when you should fertilize in the garden depends on the plant itself, how it is used and the type of fertilizer. Sure: plants need nutrients!
Mineral or organic fertilizer?
Mineral fertilizer is immediately available to plants. However, it can be washed out quickly in sandy soils. Therefore you should only apply it here in small amounts, but more often. In contrast to this, organic fertilizers such as horn meal first have to be broken down by the soil organisms, but then they also keep well in light soils. Horn meal and shavings are made from the horns and hooves of cattle. It is ideal for the garden because it contains mainly nitrogen and only a small amount of phosphate and potassium.
Improve humus soil with compost
Organic components are of crucial importance for soil fertility. In the top 10 to 30 cm, they are converted into humus by the soil organisms, which in turn can be absorbed by the plants in the form of nutrients. If you want to increase the amount of humus in the soil, it is best to use compost. After all, vegetable waste that is generated in the garden and in the kitchen is converted into a valuable soil improver via the compost.
You can of course also use purchased compost, for example made from bark, for this purpose. The compost gets into the ground by mixing one or two handfuls of well-rotted material into the excavation when planting the plants. Furthermore, every year in March and April, 2 to 3 kilograms per square meter of mature compost are worked into the top 15 cm of soil. In the case of poor and light soils, it can also be up to 10 kg. A year-round mulch cover made of half-rotted compost material does the rest to improve the humus content and thus the soil structure and soil fertility over the long term.
Buy garden soil: what is important?
Your own garden soil is often not enough for flower boxes, indoor plants or the raised bed. Even if the soil in your own garden is polluted with pollutants, it is better to use potting soil from the garden center or hardware store. This soil is specially designed for certain plants. Potting soil or plant humus from the garden center is always a mixture of different components, which together create ideal conditions for the respective type of plant.
Aeration, water storage, structural stability and nutrient storage play an important role in this. In peat-free soils, green waste compost, bark humus, clay minerals, wood fibers and coconut fibers are mixed. Green waste compost serves as a nutrient supplier, wood and coconut fibers ensure good ventilation and improve the stability of the substrate. Clay minerals in turn improve nutrient storage and release as well as water storage. The pH value and fertilizer in purchased potting soil are also already matched to the plants.
Cultivation soil e.g. contains little fertilizer, but tomato soil contains a lot. The majority of the soils sold in garden centers and hardware stores contain peat. Peat is a finite raw material; sensitive ecosystems are destroyed when it is extracted. Therefore, the use of peat in private gardens can hardly be justified. When buying, make sure that the soil is completely peat-free. To ensure that they are definitely free of peat and not just “organic” or “reduced peat”, the packaging must say “peat-free” or “without peat”.