How to Know If Soil is Clay

Clay is used in making adobe.

Soil is classified into four different types: clay, loam, sand and silt. Clay particles are the smallest of all soil particles, making clay the densest soil type. As a soil medium, clay is best suited for moisture and mineral retention although once depleted of these traits, it becomes extremely difficult to work with and requires considerable reconditioning to return it to a favorable state. For plants, root penetration into clay is burdensome and in landscaping, dehydrated clay can open fissures, leaving wide cracks in a lawn. Determining if soil is clay can be achieved using some low-tech testing methods.

Things You'll Need

• Shovel
• Glass jar, quart size
• Measuring tape

Instructions

Field and Ball Testing

1. 

   Check soil pH levels while testing.

   Testing soil in the field requires that you dig a hole 1 foot wide and 1 foot deep at the lowest point of the testing area while the soil is evenly moist. Shape the sides and the bottom of the hole as evenly and as level as possible.

2. Fill the hole with clear water and allow the water to calm. Check the water level immediately. Ideal soil will drain in 30 minutes. Water still standing in the hole the following morning is a good indication that the soil is primarily clay.

3. 

   Test several areas before planting.

   Gather a handful of soil into your hand for the ball test. Squeeze the soil evenly and release. Examine the contents and characteristics of the soil. Soil that breaks apart quickly or has no continuity at all is indicative of sand.

4. Squeezing soil into a ball that holds its shape and that feels like plastic or lacks elasticity is a good indication of clay soil. Pressing a handful of soil into a ball that retains some of its shape and has some elasticity is soil ideal to the grower.

Jar Test

1. 

   Allow an air gap for circulation during the jar test.

   Fill a clear and clean 1-quart glass jar 1/3 full of soil. Fill the jar to the neck with clear water, secure the lid and shake the contents vigorously for two minutes. Allow the contents to settle.

2. Use a black marker to make a level line across the outside of the jar to determine the soil content. After two minutes, mark a line on the jar at the visible line of settled content to indicate the amount of sand that has settled at the bottom.

3. Wait one hour for the loam layer to solidify and mark a second line at the top of the settled content. Mark a third line 24 hours after the contents have completely settled to determine the layer of clay within the jar. Measure the levels of soil with a measuring tape to determine the content of clay.

References

• Colorado State University Extension: Estimating Soil Moisture; D.L. Miles; Feb. 2006
• Gardening Know How: How to Tell if Your Soil is Clay
• Global Garden Studies: Soil Types and Testing

Resources

• "Old-Time Gardening Wisdom"; Jerry Baker; 1999