USDA Soil Texture Types

Many people focus on diseases and pests when gardening as these are generally the most visible problems, but a full 80% of a garden’s problems begin with the soil. Knowing what you are starting with is the first step toward fantastic, productive gardens.

Your garden soil will fall into one of three general categories classified by its mineral content and texture: Sand, Silt, or Clay. Most likely it will be a type of clay or sandy soil as most of the soils in our area generally fall into one of those two categories. I will discuss these two in more detail below.

The fortunate gardener may find themselves in possession of the holy grail of soil types: loam. Loam soils are balanced soils with a proportion of sand, silt, clay (40-40-20). If you find that you do not possess this soil type, don’t lose hope!

While you cannot change the basic character of your soil, you can build your garden style around it by choosing the types of plants and amendments to use and how to interact with your soil to bring out its greatest potential.

Determining your Soil Type

You could hire a professional to sample your soil but for most home gardeners it is enough to identify one’s own soil by the following two methods.

A Guide to Texture by Feel

By Feel

Judging your soil type by feel can be a bit of an art form and takes practice. Click on the flow diagram to the left. It takes you step by step through the process.

The Jar Method

  1. In a 1-qt jar with a tight-fitting lid, add about four inches of your garden soil.
  2. Fill the remainder with water nearly to the top, replace the lid securely, and shake the jar vigorously. Clay soils may require a dispersing agent such as a teaspoon of salt and longer, more vigorous shaking.
  3. Allow the water and soil to settle, undisturbed, for 24 hours.
  4. Within the first few minutes the larger particles (sand) will settle to the bottom. Mark this layer on the jar with a sharpie.jar-method
  5. Silt will settle over the next 3 to 4 hours. Mark this level with a sharpie.
  6. Clay particles will take the remainder of the 24 hours to settle, some of the smallest particles may never leave the suspension.
  7. The organic matter will float on top of the water.
  8. After you have marked all the lines, you can roughly judge their proportions to decide what soil type you have.

You Soil is Predominantly Clay

Clay soils are composed of very fine textured soil particles. While nutrient rich, in the garden they tend to compact easier, whereby the fine soil particles create a tight lattice that holds water. This can be problematic as most plants prefer good drainage. The density of these soils not only makes them heavy but can also impede plant roots if the structure of the soil is in poor condition. Clay soils are also cold soils in the spring with their high water content and can become incredibly hard in the summer under the baking sun.

What you can do.

The best way to improve clay soils is to protect its structure. With proper care, clay soils can form aggregates where individual particles glom together with the help of time, mycorrhizae, earthworms, soil microorganisms and plant roots. This process increases the pore space (space between individual aggregates) and thereby its permeability – drainage. Avoid compacting it by tilling, walking on it, or working the soil when it is wet (after rain or in early spring). Clay soils are best suited for perennial plantings where interaction with the soil is limited.  If you have your heart set on a vegetable garden or annual garden that requires frequent plantings, consider creating a raised bed for increased drainage and workability.

Increasing drainage and permeability is the goal when amending clay soils. The best additions are fibrous organic amendments such as peat, straw, and composted mulches.3 Never add sand to clay soils as this can create a soil similar to concrete. Adding organic matter yearly helps promote the services of mycorrhizae, earthworms, soil microorganisms improving the soil structure.

When adding amendments, mix them into the first 4-6 inches in order to reap the benefits of the amendment but as stated earlier, avoid tilling once these additions have been made. Applying a thick layer of mulch to the surface of the soil will also help improve its structure and reduce the risk of compaction.4

The Royal Horticultural Society has a great (and detailed) resource for gardening with clay soils.

You have Sandy Soil

Sandy soils with their large pore spaces drain freely and because of this they often have difficulty retaining moisture and water soluble nutrients. Sand particles do not bind minerals easily and are often nutrient poor. These soils are considered ‘light’ soils and are generally easy to work. They also warm quickly in the spring which is a benefit with our short growing season.

What you can do.

Increasing water retention and soil fertility are the goals when amending sandy soils. Amend these soils frequently with organic matter. Choose peat, compost, and aged manure amendments. Adding supplemental fertilizer throughout the season will keep your plants growing strong.

Irrigate these soils using smaller doses more frequently. Overwatering does not help plants growing in these soils as the excess water drains away taking with it any soluble nutrients.

Choose plants that love great drainage and thrive on lean soils. Lavender and sage are two plants that spring to mind.

Learn more:

Look up your area online at the ‘Web Soil Survey‘.

Resources:

1 – Soil Texture
2 – Soil Texturing in a Quart Jar
3 – Choosing a Soil Amendment.
4 – The Myth of Soil Amendments Part II: “If you have a clay soil, add sand to improve its texture”