healthy soils

The key factors for growing food and healthy plants are soil, sun, air, water. Today, let’s focus on the basics of soil!

The soil you encounter outdoors differs from location to location based on the rocks in the area, which have eroded over time to create the soil. This physical basis of the soil is called soil texture and it’s the “feel” of the soil. It’s a property of the soil and is measured as the proportion of sand, silt, and clay particles. Texture affects a soil’s ability to drain water, allow air flow, and hold nutrients. Knowing your soil’s texture is a great starting place to knowing what your plants need to thrive.

One of the most common tools used to understand soil is the soil textural triangle. Developed by the United States Department of Agriculture in the first half of the 1900s, the triangle is still in use today. The triangle demonstrates the three primary mineral particles that give soil its texture and make up the non-living parts of the soil: clay, silt, and sand. Most natural soils have a mix of all three particles, in addition to a thriving system of living organisms, water, air, and organic matter.

How can you determine the texture of your soil?

You can assess soil texture in minutes using the ribbon test!

1. Collect a handful of soil from 3 – 4 inches below the surface.
2. Break up the soil with your hand and remove rocks or large soil clumps that don’t break down.
3. Mix a little bit of water into the soil (if it’s not already moist) and knead it until it feels like putty. If you add too much water, add more soil until you can easily roll the sample into a moist ball.
4. If the sample never forms a ball, you have sandy soil.
5. With the ball in one hand, gently squeeze and push the soil between your thumb and index finger to create a ribbon. If the soil breaks before it forms a ribbon, you have loamy sand.
6. Push the soil until the ribbon breaks under its own weight. The ability to form a ribbon and the length of the ribbon indicate the soil type.

Reading your results:

To further differentiate the soil after the ribbon test, take a small pea-sized amount of soil and wet it in the palm of your hand. Rub your finger over the soil in your palm.

• Sand is the largest soil particle. A sandy soil will feel very gritty when rubbed between your fingers.
• Silt is the second-largest particle. A silty soil will feel smooth and silky. It is often compared to the feeling of flour.
• Clay is the smallest particle. Heavy clay soils feel sticky when wet and can look like cat litter when dry. Clay soil is difficult to determine by feel and is usually determined by the absence of an overwhelming feeling of grit or smooth texture.

Finding the texture of soil takes practice. Even soil scientists disagree about a soil’s texture! But with more practice you can start to understand differences that impact your plants.

This guide was prepared based on the USDA NRCS “Guide to Texture by Feel”

What does soil texture mean for your plants?

In Washington County, Oregon, we most often encounter silt loam, silty clay loam, and clay soils.

If you have sandy soil (more sand than clay or silt), your soil will hold fewer nutrients and water. Plants that thrive in dry conditions will do well. Plants will need frequent watering and fertilizing in sandy soil.

If you have silty soil (more silt than sand or clay), your soil holds nutrients and water fairly well (though not as well as clay). Most plants will do well with routine watering and fertilizing. Applications of organic matter can help create better soil structure.

If you have clay soil (more clay than sand or silt), your soil holds nutrients and water. Plants that don’t mind being in wet environments will do well in clay because it takes a long time for water to drain from the soil. Plants will need fewer nutrients and water and will do well with more applications of organic matter to allow air flow and water movement.

If you have loamy soil (a mix of sand, clay, and silt), your soil is well-balanced and most plants will thrive with routine watering and fertilizing.

More resources to know your soil!

• Learn more about soil characteristics and tests.
• Print out our handy Do-It-Yourself Soil Testing handout to practice soil texturing and measure your soil’s biological activity.
• Consider the importance of healthy soil for growing your own food.