Soil texture

The texture of soil refers to the relative proportions of sand, silt and clay in the soil. Sand represents the largest sizes mineral particles in the soil (other than stones and larger rocks), silt particles are smaller and clay particles are the smallest.

The texture of the soil will vary significantly depending on how much sand, silt and clay it contains. The different textures are often illustrated by a triangular chart indicating the percentage (%) of each particle size within the soil. The classifications vary slightly from region to region, for example these are the soil textural triangles for the USA and England/Wales:

The size of mineral particles in the soil is important because it determines the size of the gaps or ‘pores’ between the particles. Ie the pores are bigger between the bigger sand particles while the pores are smaller between the smaller clay particles. The larger the pore sizes the more freely water drains from the soil and, therefore, air can enter the soil more readily.

Loams are combinations of sand, silt and clay. When the proportions of each part are more or less equal it is known as ‘loam’. Where one type of particle dominates, for example sand, it is known as sandy loam.

These are the generalised characteristics of the three main soil types:

Sandy soil

• Easy to work, but problems can be caused if the particles pack together too closely and therefore become compacted or panned (eg if the soil is firmed too enthusiastically or has heavy traffic use).
• Free draining, so it doesn’t retain water and can be vulnerable to drought.
• Changes in the pH (particularly increased acidity) can have a rapid impact on sandy soils.
• Warm up quickly in the spring (because of the easy exchange of the colder soil air for the warmer atmospheric air), which means you can sow earlier.
• Nutrients are easily leached from the soil because it’s so free draining.

Silty soil (also applies to very fine sandy soils)

• Good water holding capability.
• Relatively easy to work, so long as there is a good level of organic matter.
• Vulnerable to surface capping and compaction as they usually have a weak structure.

Clay soils

• Slow draining, so plants can experience waterlogged conditions more often than with sandy/silty soils.
• Slow to warm up in the spring, so can’t sow as early.
• Soil is too sticky to work until it has had time to dry out a bit, so you can’t work it at all during or immediately after a significant rainfall.
• Tends to retain nutrients better and any changes in pH won’t effect it as quickly or significantly.

You can assess the texture of your soil by feeling wetted soil, by letting the soil settle in water or by using gradually smaller sieves to divide the soil into its different sizes (this is not a feasible solution for most domestic gardeners).