Soil types, such as clay, sand and silt, are compositions of different size rock particles, which affects a soil’s nutrient and water holding capacity and drainage. They aren’t as important as made out as every plant will adapt to its conditions and every soil type is improved the same way – through maintaining plant life and adding organic matter.
What are soil types?
When people are talking about soil types, they are usually referring to soil texture. A soil’s texture is determined by the composition of rock particles in the soil. These particles come in different sizes, and the smallest are known as the fine earth fraction, which range from the largest sand (.05-2mm) to the smallest clay (<.002mm) with silt (.002-05mm) in the middle.
Within clay are very small particles (0.0001mm) known as colloids. Colloids have the ability to absorb, hold and release nutrients and are important as without nutrients would simply leech away. This occurs as they are negatively charged and attract positively charged ions such as nutrient atoms and water molecules, which bind to the surface. Hence, as particle size decreases, water and nutrient holding capacity increases.
From this, we arrive at the different properties each soil texture possess. Clay and silt are rich in nutrients and have good water holding capacity, but drain poorly, and are vulnerable to being waterlogged. Sand is poor in nutrients and water holding capacity, but drains quickly. Loam famously has the best properties of any texture.
Soil is composed, not just of rock, but decomposed organic matter known as humus. Silt and sand particles are bound to clay and humus particles forming peds (aggregates). All soil types benefit from adding organic matter and maintaining plant life.
In clay soils, adding organic matter acts to increase aggregate size, decreasing the amount of macropores, improving drainage. In sand, adding organic matter acts to increase the amount of micropores, improving the water holding capacity. This is because organic particles can also be very small (colloids) but are even more chemically reactive.
So how does organic matter improve silt and loam soils? Organic matter provides feed for plants and soil organisms that act to increase the porosity of the soil and break down minerals into soluble forms.
Chalk and peat soils are slightly different. Chalk soils can be made up of different particles sizes, but are notable for being alkaline. Peat soils are heavily organic and are often acidic.
Are soil types important?
Soil types aren’t as important as made out as every plant will adapt to its conditions. Most plants are planted/seed in suboptimal conditions and provide good results. More important is how you look after the plant, such as whether you water, fertilise and apply mulch. Planting is critically important. Avoid compacting the soil or otherwise a soil’s porosity will be reduced.
Now, it’s important to avoid waterlogged soils, which act to starve a plant of oxygen, causing root rot, and eventually root death. pH is also important. Camellia, rhododendrons, and blueberries will not do well in neutral or alkali soils, so are best grown in pots.
What’s the best soil for pots?
Using a mix of garden soil and compost will produce the best mix of macropores and micropores. Again, care is key. Potted plants are especially liable to drought, so be sure to apply mulch, which helps trap moisture. Ensure you drill a hole in the bottom of the pot, so water can drain.
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Jorge works in the Primrose marketing team. He is an avid reader, although struggles to stick to one topic!
His ideal afternoon would involve a long walk, before settling down for scones.
Jorge is a journeyman gardener with experience in growing crops.