Soil science binds topsoil, planting and paving work together. Here is soil science: soil components, grain sizes and texture, JB classification, soil structure, plant-available water and how soil type determines drainage, bearing capacity and frost heave.
Introduction
All site landscaping work rests on soil — literally. Soil type determines whether water seeps or stands, whether a paving carries or sinks, and whether plants thrive or languish. Therefore soil science is essential knowledge that connects composting, planting, drainage, and paving work: know the soil, know what must be drained, improved, or replaced.
Earth's components
Good growing soil is not solid mass, but a mixture of solid parts and voids. Mineral particles (sand, silt, clay) and organic matter (humus) make up the solid, whilst pores between particles contain water and air. The balance is crucial: plant roots need both water and oxygen, so soil without air (e.g. compacted or waterlogged) suffocates the roots, whilst soil without water-holding capacity dries out.
Grain sizes and texture
Earth's texture is determined by how large the mineral particles are. In the Danish soil classification system, the mineral part is divided according to grain size:
| Fraction | Grain size | Meaning |
|---|---|---|
| Coarse sand | 2–0,2 mm | Drains quickly, no coherence, low nutrient holding capacity |
| Fine sand | 0,2–0,02 mm | Drains well, easy to work |
| Silt | 0,02–0,002 mm | Fine-grained, dangerous for phone, can seal up |
| Ler | under 0,002 mm | Binds water and nutrients tightly, compacts and structurally damaged easily |
The texture triangle is the helper tool: from the percentage content of sand, silt and clay, the soil's texture class is read from a triangle with the three fractions in each corner. Add to this humus (organic matter), which affects structure, colour and nutrient pool.
JB-classification
Danish soil is divided into JB classes (soil type classification) by the content of clay, silt, sand and humus. The higher the JB number, the more clay — up to JB9; JB10 is silty soil and JB11 humus soil. The class briefly tells how the soil behaves:
| JB-gruppe | Soil type | Properties in broad strokes |
|---|---|---|
| JB1–JB4 | Sandy soil | Drains quickly, dries easily, low nutrient holding capacity |
| JB5–JB6 | Sand-mixed clay soil / clay-mixed sandy soil | Balanced — often good cultivation/growing soil |
| JB7–JB9 | Clay soil | Retains water and nutrients but compacts and structurally damaged easily |
| JB10 | Silt soil | Fine-grained, dangerous for phone, can seal up |
| JB11 | Humus soil | High organic content, settles and oxidises during drainage |
Soil structure
Structure is the way soil particles clump together in aggregates (crumbs). Good crumb structure provides stable pores that water and air can move through, and that roots can grow through. The structure is damaged when you drive on or work the soil in wet condition — especially clay soil is smeared and compacted, so the pores are pressed together, and the result is dense, oxygen-poor soil that neither drains nor supports plants well. Protect the structure: do not drive on wet soil, and avoid unnecessary compaction of the topsoil.
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