Sometimes it is important to know what type of soil you have in your own garden. But what types of soil are there? The soil can be tested and determined with the finger test.
Do you have "good soil"? Many garden owners - especially new ones - can hardly answer this question or only with great uncertainty. We know from hearsay what kind of soil is in the area. But what if someone else's soil was distributed on one's own property? And is it true what the neighbors are saying?
You can find out what kind of soil you have with our quick guide to checking soil type. This allows you to see how well certain plants or even the lawn feel on your floor.
What types of soil are there?
Floors are made from very different raw materials, i.e. rocks, and have been formed over thousands of years. The weather, temperatures, water movement and the entry of rock dust and organic materials all left their mark. Every floor is unique due to its individual history of origin. Nevertheless, for the comparability of soils it is important to classify them - namely into soil types.
The soil types are based on the different grain sizes that occur in a soil. So they reflect how many very small, medium-sized or very large particles make up the soil. Soil particles can be far less than a micrometer in size, or even over 20 cm.
The many different grain sizes are grouped into fractions, i.e. groups with similar grain sizes, and are called sand, silt and clay. Sand is the coarsest grain, silt is medium-coarse and clay is the finest grain. The type of soil depends on the ratio in which these three soil components are mixed. To visualize this, the soil type triangle is a useful tool.
Tip: Clay is not a separate particle size fraction. Soils are referred to as clay, which all threeCombine grain sizes in similar proportions. Roughly speaking, loam consists of similar proportions of sand, silt and clay. They are considered to be particularly fertile soils. On the other hand, soils that mainly consist of one particle size are rated as unfavorable for plant growth.
Sandy bottom
Sands can be found in the bottom left corner of the soil type triangle. Soils with a high proportion of sand are very permeable to water due to their primarily coarse grain size, so they can hardly store any water. However, waterlogging hardly ever occurs on such soils.
Sandy soils are very well aerated, oxygen can easily penetrate between the coarse grains of sand. Plant roots can very easily take root in sandy soil and air-breathing microorganisms also feel extremely comfortable here. The very active microorganisms break down organic residues in the soil quickly, but unfortunately there is hardly any humus. Due to the usually low humus content, sandy soils are poor at storing nutrients and are generally considered to be poor in nutrients.
But sandy soils are easy to work with, because the sand does not stick to each other or to garden tools. In addition, it doesn't get heavy when it rains because it hardly absorbs any water. Therefore, when speaking of light soils, sandy soils are always meant.
Sandy soils have an unstable pH value and are easily influenced by lime and acids.
Sands include pure sands, loamy sands and silt sands. In Germany, for example, very sandy soils can be found in the Lüneburg Heath and the entire Heidekreis, where they were formed from the end moraine of the glaciers of the last ice age.
By the way: Due to their low storage capacity, sandy soils have to be fertilized and watered regularly, but in small doses.
Silt soil
Silts are shown at the top of the soil type triangle. Due to its medium grain size, silt is also in its properties in the middle between clay and sand. The pore size of silt is particularly favorable for plant growth: the spaces between the individual soil particles are of a size that absorbs water well, similar to a sponge. However, because the pores are not too small either, they release the water without much resistance, for example when plant roots create a negative pressure to absorb water. For this reason, silt soils are often particularly good locations for plants and develop into the most fertile fields,meadows and natural landscapes. Similar to clay soils, silty soils provide a satisfactory habitat for microorganisms and also tend to build up a lot of humus. As a result, silty soils are good nutrient and water reservoirs, which are very loose and easy to work with.
Silts include sand silt, clay silt and clay silt.
Fertile clay silt can be found, for example, in the foothills of the Alps around Memmingen in Bavaria.
By the way: Unfortunately, silt is in danger of being blown away when it is dry due to its low level of adhesion. Silt soil should therefore always be planted and never lie fallow.
Clay soil
Tone can be found in the soil type triangle at the bottom right. Clay particles are the smallest granular fraction found in soil. Anything smaller than 0.002mm is considered clay. Due to its small grain size, clay also only has tiny pores between the particles, which bind a lot of water. However, the water will also hold on so tightly that most plants can hardly use it. Clay minerals are able to shrink and swell. When they have sucked up water, there is hardly any air left in a clayey soil. There is hardly any soil aeration on very clayey soils, which many plants and microorganisms do not tolerate well.
In addition to water, clay minerals can also store some nutrients very well and are therefore often nutrient-rich. Because clay absorbs so much water, then sticks together and becomes extremely hard when dry due to shrinkage, it is difficult to work with. When talking about heavy soil, this means a soil rich in clay.
Soil that is too clay inhibits the formation of humus, because pure clay soil is too hostile for microorganisms and other soil organisms. However, a good proportion of clay in the soil can also stabilize humus, because clay minerals form so-called "clay-humus complexes" with humus molecules, which are very difficult to break down and make the soil extremely fertile.
Clay soils have a very stable pH and are only very slowly affected by lime or acids. Clay soils include silt clay and loam clay.
Silt clay, for example, can be found on both sides of the Elbe on the entire route from the North Sea to Hamburg - no wonder that fruit growing is flourishing there, because many fruit trees love clay soil.
By the way: Clay can hold a lot of waterstore water, but plants cannot necessarily use this water. In order to be able to grow different plants, heavy clay soil often has to be mixed with sand. If plants are to be grown in clay soil, it is particularly important to ensure the build-up of humus or to use high-quality potting soil and compost.
clay soil
Loams are located in the center of the soil type triangle. They are a good mix of silt, sand and clay. Their properties are considered to be particularly favorable for many plants, because they have everything “mediocre” at their disposal: they store a moderate amount of water, a large proportion of which can also be used well by plants. With the help of the right humus management, they offer a high potential to build up a lot of fertile humus. Loamy soils can store a lot of nutrients and moisture in their clay content and also in the humus and are therefore usually rich in nutrients. Good soil aeration is also guaranteed with a sand content of at least 30%.
Loamy soils can, however, be difficult to work with due to their ability to store a lot of water and to cement themselves together.
The loams include sandy loams, normal loams and clay loams.
Normal loams can be found, for example, in the Swabian-Bavarian old moraine landscape around Munich, and enable flourishing agriculture there.
Tip: Difference between soil types and soil types
The terms soil type and soil type are often used interchangeably. However, the soil type only refers to the topsoil, i.e. the part of the soil with the strongest root penetration. The soil type, on the other hand, contains a variety of other information, namely about "soil genesis", i.e. the formation of the soil. Unfamiliar-sounding names such as Rigosol, Gley, Anmoorgley, Pseudogley, Parabraunerde, Reductosol, Ranker or Schwarzerde include the basic soil material for soil scientists. In addition, they provide information about its state of development and thus its age and the soil horizons it contains.
Determine soil type: Finger test on the soil
The finger test is a simple and amazingly reliable way of determining soil type. The more different soils you have in your hands, the more reliable the assessment becomes. In order to be able to interpret the finger test, one must be aware of the properties of the 3 grain sizes:
- Sand feels grainy, rough and scratchy. It doesn't stick in the finger grooves.
- Silt feels velvety floury and is hardly cohesive. When you smear silt, the smeared surface does not shine. Silt sticks strongly in the finger grooves.
- Clay tacky to the touch and highly cohesive. That's why it's easy to shape. Smearing clay makes a shiny smudge.
Perform finger test: step-by-step instructions
- Take soil sample: Take samples distributed over the entire examined area. Soil from a depth of 5 to 20 cm is suitable for the sample. Discard the top 5 cm of each sample as it may be too heavily contaminated with organic matter and plant debris. Mix all samples well in a bucket.
- Set moisture: The mixed sample should have a medium moisture level, i.e. it should be neither wet nor dry. One speaks of the "culture moisture" because the water content appears as if it were just right for plants. Spread soil that is too wet and let it dry a little, slightly moisten soil that is too dry with a spray bottle.
- Sample 1 - roll test: For this purpose, a walnut-sized part of the sample is kneaded together firmly in the hand. Then it is rolled out in the palm of the hand like playdough into a roll the thickness of a pencil.
| Observation | Interpretation |
| Sample cannot be rolled out at all | Base of soil is sand |
| Sample can only be rolled out once, crumbles when rolled out again | Base of soil is silt |
| Sample can be rolled out and kneaded repeatedly | Base of the bottom is clay |
- Sample 2 - Rub Sample: A handful of the sample is considered.
| Test | Observation | Interpretation |
| Rub sample between fingers | Floor feels mainly rough/scratchy | High proportion of sand |
| Floor feels especially velvety | High proportion of silt | |
| Most of all, the floor feels greasy | High pitch | |
| Floor feels undefinably both grainy and greasy and velvety | Mixed soil/clay soil |
- Test 3 - Visual comparison and adhesion test: This is whereviewed a handful of the sample.
| Test | Observation | Interpretation |
| View sample, move in hand | Visible grains | Contains sand |
| Fine dust sticks in the finger grooves | Contain silt | |
| Floor is very dark | Contains a relatively large amount of hummus |
The finger check is error-prone in certain cases:
- Samples that are too dry are estimated to be grainier/sandier
- Samples that are too moist are estimated to be more cohesive/clayy
- Highly humus-rich soils are misjudged because humus "mediates" both light and heavy soils: clay and sand contents are then estimated too low and silt contents are estimated higher.
If you don't trust yourself to assess the type of soil or need more information about your own garden soil, specialized laboratories such as the Raiffeisen Laboratory Service offer a good, but of course not free, alternative. In addition to the soil type, a soil analysis also determines the pH value and the content of some nutrients.
Humus may interfere with soil analysis a bit, but it serves as a nutrient and water reservoir in soil and loosens the structure so that plant roots grow better. It is food for soil organisms and a crucial component of fertile soils. Every soil type improves with an increase in humus content - reason enough to use our guide to proper humus management to increase the humus content of your own garden soil!