Soil Types
Soil is the loose, upper layer of earth in which plants grow.
Soil is a mix of organic material, clay, silt, sand and rock particles laying on top of the bedrock.
Soil Horizons
Soil horizons are the distinct layers of a soil profile:
| Name | Description |
| o - Humus | Organic material |
| A - Topsoil | Where plants grow |
| B - Subsoil | Where the roots go |
| C - Parent | Original rock deposit |
| R - Bedrock | The solid rock |
Soil Particles
Scientists have classified soil particles into the groups: Clay, Silt, Sand, Gravel and Pebbles.
| Name | Size in mm | Description |
|---|---|---|
| Clay | < 0.002 mm | Formed by weathering and erotion of rocks. Clay particles are very small. Clay tend to pack, so water cannot drain and air cannot penetrate. |
| Silt | 0.002 - 0.050 mm | Rock dust formed on the bottom of a water body. Silt particles are medium sized and have properties in between those of sand and clay. |
| Sand | 0.050 - 2 mm | Broken rocks and minerals (Silicia quartz). Sand particles are large. Sand holds little water but allows good aeration. |
| Gravel | 2 - 4 mm | Small, rounded stones, often mixed with sand. |
| Pebbles | 4 - 64 mm | Rounded stones found on a beach or in a river. |
Soil Textures
Image from USDA Natural Resources Conservation
| Name | Clay | Slit | Sand |
|---|---|---|---|
| Clay | 80% | 10% | 10% |
| Sandy Clay | 50% | 0% | 50% |
| Silty Clay | 50% | 50% | 0% |
| Loam | 20% | 40% | 40% |
| Silty Loam | 20% | 70% | 10% |
| Sandy Loam | 20% | 10% | 70% |
| Silt | 10% | 80% | 10% |
| Sand | 10% | 10% | 80% |
Clay
Clay soils have the finest particles and are known for their water retention capacity.
Clay soils contain more than 30 percent fine clay particles. Some clays swell and shrink as they wet and dry, which can add to soil fertility.
Clay soils take longer to warm up in spring. Wet clay soils are easily damaged when dug or walked on.
Drought is much less damaging on clay soils than others soil types.
Wet Clay
Dry Clay
Red Clay
Pros: Holds water and nutrients the longest of all soil types. Less susceptible to drought.
Cons: Prone to compaction. Callenging for root penetration. Poor drainage.
Silt
Silty soils have medium-sized particles, smaller than sand, larger than clay.
Pros: Fertile. Water retaining. Less susceptible to drought.
Cons: Poor drainage. Prone to contration. Similar to clay.
Sand
Pure Sand
Loamy Sand
Coarse Sand
Sand is a granular material composed of mineral particles smaller than gravel and coarser than silt.
Sand warms up quickly in the spring, aiding early vine growth, but can dry out quickly.
Pros: Great drainage. Mineral Rich. Heat retaining. Phylloxera free.
Cons: Poor fertility. Susceptible to drought.
Loam
Loam is a combination of clay, silt and sand.
Pros: Good drainage. Very fertile. Retains nutrients and water.
Cons: Too fertile for vineyards.
Gravel
Gravel are aggregates of more or less rounded rock fragments coarser than sand.
Pros: Good drainage. Retains heat.
Cons: Infertile. Poor water retention.
Pebbles
Pebbles are small stones made smooth and round by the action of water or sand.
Pros: Great drainage. Retains heat.
Cons: Infertile. Roots have to dig deep to find nutrients. No water retention.
Vineyard Soils
Alongside climate and grape selection, vineyard soils play a crucial role in the quality and characteristics of wines. Different soils provide us with the different regions and areas that produce the world most famous wines.
Soils influence everything important for grapevine health and grape quality:
- Water drainage and water retention
- Water and Nutrient availability
- Vine stress and root development
- Heat assumption and heat retention
It is also important to know that soil can be different across wine-growing regions. It can even be different across a single vineyard.
Most vineyards are a blend of stones, gravel, top soil and deep soil.
