Sometimes it is important to know what type or type of soil you have in your garden. But what types of soil are there anyway? The soil can be tested and determined with a finger test.
Do you have “good soil”? Many garden owners – especially new ones – can hardly answer this question, or only with great uncertainty. From hearsay, you know what soil is in the area. But what if someone else’s land was once distributed on your property? And is what the neighbors say is true?
You can find out what type of soil you have with our quick guide to checking soil type. This enables you to see how comfortable certain plants or even the lawn feel on your soil.
What types of soil are there?
Soils are made from very different raw materials, i.e. rocks, and have been shaped over thousands of years. Weather, temperatures, water movement, and the entry of rock dust and organic materials left their traces. Each floor is unique due to its individual history. To be able to compare soils, however, it is important to classify them – into soil types.
The soil types are based on the different grain sizes that occur in 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 or over 20 cm in size.
The many different grain sizes are summarized infractions, i.e. groups with similar grain size, and called sand, silt, and clay. Sand is the coarsest grain size, silt is medium-sized and clay is the finest grain size. The type of soil depends on the ratio in which these three soil components are mixed. The soil type triangle is a useful tool to visualize this.
Tip: Clay is not a separate grain size fraction. Soils are called loam which combines all three-grain sizes in similar proportions. So loam consists – roughly speaking – of sand, silt, and clay in similar proportions. They are considered particularly fertile soils. Soils that consist primarily of one-grain size, on the other hand, are rated as unfavorable for plant growth.
Sands can be found in the soil type triangle in the bottom left corner. Soils with a high proportion of sand are very water-permeable due to their predominantly coarse grain, so they can hardly store water. However, waterlogging rarely occurs on such floors.
Sandy soils are very well ventilated, and oxygen can penetrate well between the coarse grains of sand. Plant roots can take root in sandy soils very easily and air-breathing microorganisms also feel extremely comfortable here. Due to the very active microorganisms, organic residues in the soil are quickly broken down, but unfortunately, there is hardly any humus. Due to the mostly low humus content, in turn, sandy soils can hardly store nutrients and are generally considered to be poor in nutrients.
Sandy soils are easy to work on because the sand does not stick to each other or garden tools. In addition, it does not become heavy when it rains, because it hardly absorbs any water. When speaking of light soils, sandy soils are always meant.
Sandy soil can also be dark if it contains a lot of humus
Sandy soils have an unstable pH value and can easily be influenced by lime and acids.
By the way: sandy soils have to be fertilized and watered regularly, but in small doses, because of their low storage capacity.
Silts are drawn in at the top of the soil type triangle. Due to its mean grain size, silt is also in the middle between clay and sand in terms of its properties. The pore size of silt is particularly beneficial for plant growth: the spaces between the individual soil particles are of a size that absorbs water well, similar to a sponge. But because the pores are not too small, 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, silt soils provide a satisfactory habitat for microorganisms and also tend to build up a lot of humus. As a result, silt soils are good stores of nutrients and water that are very loose and easy to work with.
Soils with a high proportion of silt are usually very fertile
The silts include sand silts, clay silts, and clay silts. Fertile clay silts can be found, for example, in the foothills of the Alps around Memmingen in Bavaria.
By the way: Unfortunately, silt is at risk of being blown away when it is dry due to its low level of adhesion. A silt soil should therefore always be planted and never lie fallow.
Clays can be found in the soil type triangle at the bottom right. Clay particles are the smallest grain fraction that occurs in soils. Anything smaller than 0.002 mm is considered clay. Due to its small grain size, clay only has tiny pores between the particles that bind a lot of water. However, the water will hold onto it so strongly that most plants can hardly use it. Clay minerals can shrink and swell. When they have soaked up water, there is hardly any air left in clayey soil. So there is hardly any soil ventilation on clayey soils, which many plants and microorganisms cannot tolerate well.
In addition to water, clay minerals can also store some nutrients very well and are therefore often rich in nutrients. Because clay soaks up so much water, then sticks together, and becomes extremely hard when dry due to shrinking, it is difficult to work with. When we talk about heavy soils, we mean clay-rich soil.
Soils that are too clay inhibit the formation of humus because pure clay soil is too hostile to life for microorganisms and other soil organisms. 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-rich soils often clump together to form large aggregates
Clay soils have a very stable pH value and are only very slowly influenced by lime or acids. The clay soils include silt clays and loam clays.
Silt clays, for example, can be found over a large area on both sides of the Elbe on the entire route from the North Sea to Hamburg – no wonder that fruit growing is flourishing there, as many fruit trees love clay soils.
By the way: although clay can store a lot of water, plants cannot necessarily use this water. 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, it is particularly important to ensure that humus is built up or to use high-quality potting soil and compost.
Loams are in the center of the soil type triangle. They’re a good mix of silt, sand, and clay. Their properties are considered to be particularly favorable for many plants because they have everything “in the middle”: They store an average amount of water, a high proportion of which is also useful for plants. With the help of the right humus management, they offer a high potential for building up a lot of fertile humus. In their clay content and also in the humus, loam soils can store a lot of nutrients and a lot of moisture and are therefore usually rich in nutrients. Good floor aeration is also guaranteed with a sand content of at least 30%.
However, clay soils can be difficult to work with due to their ability to store a lot of water and cement together firmly.
Clay soils are a mixture of sand, clay, and silt and are also particularly fertile
The clay loams include sand loam, normal loam, and clay loam. Normal loam 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 synonymously. The soil type, however, only describes the topsoil, i.e. the part of the soil with the most roots. The soil type, on the other hand, contains a large amount of additional information, specifically on “soil genesis”, i.e. the formation of the soil. Alien-sounding names such as Rigosol, Gley, Anmoorgley, Pseudogley, Parabraunerde, Reduktosol, Ranker, or black earth are the basic material of the soil for soil scientists. They also 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 to determine the type of soil. The more different floors you have in your hands, the more reliable the assessment will be. 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 does not stick in the finger grooves.
- Silt feels velvety floury and is hardly cohesive. If you smear silt, the smeared surface won’t shine. Silt sticks strongly in the finger grooves.
- Clay feels sticky and is strongly cohesive. That is why it is easy to shape. If you smear clay, it gives a shiny smear surface.
To get meaningful results, it is important to take a mixed sample
Carry out a finger test: step-by-step instructions
- Taking a soil sample: To do this, take samples distributed over the entire investigated area. Soil from a depth of 5 to 20 cm is suitable for the sample. For each sample, discard the top 5 cm, as it could be too heavily contaminated with organic material and plant residues. Mix all samples well in a bucket.
- Set humidity: The mixed sample should have a medium humidity, i.e. neither wet nor dry. One speaks of the “culture moisture” because the water content acts as if it were just right for plants. Spread soil that is too wet and let it dry a little, dampen soil slightly with a spray bottle if it is too dry.
- Sample 1 – Roll sample: For this purpose, a walnut-sized part of the sample is first kneaded firmly in the hand. Then it is rolled out on the palm like modeling clay into a roll the thickness of a pencil.
|Sample cannot be rolled out at all||The base of the soil is sand|
|The sample can only be rolled out once, it crumbles when it is rolled out repeatedly||The basis of the soil is silt|
|Sample can be repeatedly rolled out and kneaded||The basis of the soil is clay|
- Sample 2 – rub sample: For this, a handful of the sample is examined.
|Rub the sample between your fingers||Above all, the floor feels rough/scratchy||A high proportion of sand|
|Above all, the floor feels velvety||A high proportion of silt|
|Above all, the floor feels greasy||High tone content|
|The floor feels indefinable both grainy and greasy and velvety||Mixed soil/clay soil|
- Sample 3 – visual comparison and adhesive test: For this, a handful of the sample is examined.
|Look at the sample, move your hand||Visible single grains||Contain sand|
|Fine dust sticks in the finger grooves||Contain silt|
|The ground is very dark||Contains a relatively large amount of humus|
The finger test is prone to errors in certain cases:
- Samples that are too dry are estimated to be grainier / sandy
- Samples that are too moist are estimated to be more cohesive/clayey
- Soils with high levels of humus are incorrectly assessed because humus “mediates” both light and heavy soils: clay and sand contents are then estimated too low and silt contents are estimated higher.
For those who do not trust themselves to assess the type of soil themselves or need more information about their garden soil, specialized laboratories such as the Raiffeisen Laboratory Service offer a good, but of course not free, alternative. In addition to the type of soil, a soil analysis also determines the pH value and the content of some nutrients.
Soils with a high proportion of humus appear dark brown or even black
Humus may interfere with the soil analysis a little, but it serves as a nutrient and water store in soils and loosens the structure so that plant roots grow better. It is food for soil organisms and a crucial component of fertile soils. Every type of soil is improved by increasing the amount of humus – reason enough to use our instructions for correct humus management to increase the humus content of your garden soil!