Soil Texture Test: The Jar Method
Soil is one of the most important factors to consider when growing food. The structure of soil is composed of soil particles, organic matter, water, air and living organisms. Understanding the kind of soil you have helps you select the type of plants that will grow well in your area, build your soil structure to increase fertility, and determine how fast water moves through your growing area. In this article, we share how to take a soil sample and estimate your soil type using only a few materials.
The “jar method” soil texture test* is a fun and easy project that growers of all ages can participate in. This activity offers a way to begin to understand your growing space.
Soil structure is composed of three types of particles – sand, silt, and clay. Sand is the largest particle, silt is middle-sized, and clay is the smallest. The combination of the soil particles in your soil make up the soil texture. The ideal soil for growing food is a mixture of all three that combine in a particular fashion to create loamy soil. Soil type can vary from location to location, and having an idea of what is in your growing area can help build the soil. Most often, growers need to add amendments to the soil to improve the growth of plants.
*Note: To receive in-depth insight into your soil profile, send your soil sample to your local extension office for further lab analysis.
Sifter, mesh sieve, or old colander
Glass jar with lid
(Allow 6 hours after filling jar on the first day, then another 48 hours for sample to settle completely.)
1. Using a hand shovel, collect soil sample(s) from your growing area.
2. Use a sifter, mesh sieve, old colander, or your hands to separate debris, sticks, rocks, leaves, roots, etc. from soil.
3. Fill jar one-third full with sifted soil.
4. Pour clean water to fill jar, leaving ½ inch at the top.
5. Add 1 tablespoon of non-foaming soap to the jar.
6. Replace lid on jar and shake vigorously until a slurry is formed.
7. Set jar on a level surface.
8. After 1 minute, use the permanent marker to mark the outside of the jar along the layer of sand that settled at the bottom of the jar.
9. Continue to leave the jar on a level spot for 6 hours.
10. Mark the next settled layer in the jar, which is the silt layer.
11. Leave the jar in a level spot for 48 hours.
12. Mark the top of the last settled layer, which is the clay layer.
13. With a ruler, measure and record the height for each layer of soil particles for sand, silt, and clay. Calculate the total height of the combined layers.
14. Use the equations and soil texture triangle below to calculate the estimated soil texture.
Soil Texture Triangle
12 classes of soil are represented on the soil texture triangle chart (below). Calculating the percentage of each of the particles determines the class of soil texture.
Use the soil texture triangle chart to help estimate your soil type based on the percentage of sand, silt, and clay in a sample. Each side of the triangle represents the percentage of the 3 soil particles.
Sand % = (Sand height) / (total height) x 100
Silt % = (Silt height) / (total height) x 100
Clay % = (Clay height) / (total height) x 100
Add Amendments to Improve Soil Health and Promote Plant Growth
Soil can be improved by adding appropriate amendments to support the health and growth of plants’ root systems. The type of plant and its preferred soil type will help you decide if amendments need to be added. The ideal soil type is loamy, which is a mix of all three textures: silt, sand, and clay.
For sandy soil, add amendments to increase the soil’s ability to hold moisture and store nutrients.
Sand amendments: compost, aged manure, leaf mold.
For silt-dominant soil, add amendments to improve soil aeration and drainage.
Silt amendments: composted manure and vegetable matter.
For clay soils, add amendments to improve soil aggregation, aeration, and drainage and to increase porosity and permeability.
Clay amendments: sand, gypsum, peat moss, wood chips, tree bark, straw.