The Surprising Simplicity of Soil Texture

Soil is often a confusing subject for laypersons and property owners, which is unfortunate, as the soil surrounding your trees is one of the most important factors influencing their health, vigor and ultimate fate. To be fair, soil science is a complicated subject, with tendrils reaching into a variety of related subjects, including chemistry, microbiology and ecology.

But with only a modest amount of effort, you can learn about the characteristics of soil and understand those factors that will influence the health of your trees. To begin, it is important to understand one of the most fundamental properties of various soils – their textures.

Particle Size

Soil texture is determined by one exceedingly simple criteria: The size of the grains. There are three primary size classes of soil particles, known as clay, silt and sand.

  • Soils comprised of the smallest particles include clays. Clay soil particles are less than 0.002 millimeters in diameter.
  • Silt particles are slightly larger than clay particles, and measure between 0.002 and 0.05 millimeters in diameter.
  • Sand particles are the largest of the three, measuring between 0.05 and 2.0 millimeters in diameter.
  • Particles larger than 2.0 millimeters are typically considered gravel.

These differences in size cause differences in the characteristics associated with various soils. For example, sand allows water to drain quickly, while silt and clay particles hold water for longer. On the flip side, sandy soils harbor more life-giving oxygen that clay soils, which are often more highly compressed, thanks to their small particle size.

A Mixture of Sizes

While soils are classified according to the size of their constituent particles, it is important to understand that “pure” samples are rare in nature. You don’t often find areas of pure silt, for example – most soils contain particles of several different sizes.

Accordingly, soils are classified by the relative proportions (by weight) of the various particles included in the entire sample. For example, a soil containing 50% clay and 50% silt is referred to as silty clay. A sample containing 40% clay and 60% sand is called sandy clay. A soil texture triangle can help you understand these ratios better.

The Ideal Recipe

While most trees have some degree of flexibility and can adapt to a variety of different soils, different species have evolved to live in different types of soils. Many cottonwoods (Populus spp.), for example, are capable of thriving in dry, sandy soils, while red maples (Acer rubrum) are able to tolerate denser clay soils.

However, most trees thrive in soil comprised of an optimal ratio of sand, silt and clay. This type of nutritious, rich soil is called loam. Loams are comprised of varying amounts of the three components, but the ideal ratio of the three is 40% sand, 40% silt and 20% clay. If you were to remove some of the sand and replace it with clay, you end up with clay loam; remove some of the clay and replace it with silt and you get sandy loam.

Use This Information to Your Advantage

The soil texture of your area will partially determine the best trees and plants for your property. While you can’t easily alter the soil texture of a large area, you can select the best species for the texture available.

If you are having trouble getting your trees to thrive, and you suspect that soil texture is to blame, give your friends at Evergreen Arborist Consultants a call. We’ll help determine the texture of your soil and suggest the best species most likely to thrive on your property.