How to Perform a Jar Test of Your Landscape Soil

A jar test is a relatively simple method for determining the soil texture of your soil.

Why should you be interested in the soil texture of your soil? Because knowing the percentages of sand, silt and clay in your soil, or in other words it's texture, you can make some educated guesses about how much to water, when to water, how much to fertilize and when to fertilize. It costs you nothing except the time and materials you are willing to commit to it.

What You Will Need

You will need a clear quart jar such as a mason jar used for canning, a lid for it so that you can shake it, 1 teaspoon of liquid dish detergent, tap water and a composite soil sample from your yard.

Taking a Soil Sample from Your Yard

You will be taking a "composite" soil sample from your yard. This means you will collect soil samples from several locations in your landscape. Think about how deep soil roots will need to grow. Trees and shrub roots may grow 24 to 18 inches deep. Small shrubs 12 inches deep. Vegetable gardens, lawns and annual flowers only 6 to 8 inches deep.

Blindly select four or five locations in your landscape. These should be random locations and don't select them because they look terribly bad or good.

Use a shovel and a 5 gallon clean bucket to collect your soil samples. Collect the soil from the surface and all the way down to the depth you think your plant roots will grow. The sample should include equal amounts from the surface all through the root zone depth of the soil. Mix these samples together thoroughly. You now have a composite soil sample from your landscape. Take 2 cups of soil from the bucket to use in the jar test.

Soil Is Composed of Sand, Silt and Clay

But these mineral components are all mixed together in your soil. The jar test separates out these three components and by measuring them in the jar, you can determine the percentages of each in your soil.

Sand. The largest size to particle in the soil. If we were to expand its size to the size of the White House, the silt particle would be the size of a limousine parked in front of the White House and the clay particle would be about the size of an orange sitting on the seat of the limousine parked in front of the White House. So it's easy to see these particles are vastly different in size.

The Jar Test

When the jar full of water and soil is shaken, these particles settle at different rates of speed; the sand particles settle quickly because they are the largest  particles. Silt particles settle out next because they are smaller than the sand particles but larger than the clay particles. The clay particles settle last and may take many hours or even days to settle. Your soil has settled into layers of different sized particles which oftentimes have different colors. The soil in the jar has finished settling out when the water above the soil is clear.

Jar test performed on a landscape soil and showing the separation of particles because of their size; sand is on the bottom, silt is in the middle and Clay is on the top. The water was clear when it was added but the organic matter in the soil caused the water to change color.

Separation all the soil particles due to settling through the water. There is a difference in sizes of the particles and a slight color change in the layers that indicate their separation.

Determining Soil Texture

You must determine the percentages of sand (bottom layer), silt (middle layer) and clay (top layer) against the total soil volume that settled in the jar.

1. Measure the total depth of the soil in the jar. In this case, the total depth of the soil was 2 1/8 inch.

2. Calculate % of sand, silt and clay. Dividing the size of each layer by the total soil measurement approximately:
52% Sand
33% Silt
15% Clay

The Soil Textural Triangle

The soil textural triangle is a measurement of the percentage of sand silt and clay. These percentages determine the textural name the soil is given.

Our soil has 52% Sand, 33 % silt and less than18%Clay. We will name this soil a LOAM, but nearly a Sandy Loam.

Irrigating This Soil

This soil is classified as a loam but may have some characteristics similar to a Sandy loam. We can assume that 1 inch of water applied to the soil will drain to about 10 inches deep.

How Deeply 1 Inch of Water Penetrates in Soils

Fertilizing This Soil

Sand does not hold fertilizers or water well. Both fertilizers and water drain through sand easily.

Clay holds fertilizer and water extremely well. As the clay content of a soil increases, it holds more water and fertilizer.

Silt is intermediate in how it holds water and fertilizer.

Since our soil is dominated by sand we should fertilize it more often than clay soils and with smaller amounts of fertilizer each time. In extremely sandy soils we might water daily during the summer months and fertilize every 4 to 6 weeks with small amounts of fertilizer each time. In soils that contain a lot of clay we might water once a week in the summer or longer. Perhaps one or two fertilizer applications would be enough for most plants.

Our soil is dominated by sand but it does have clay and silt in it. This means water drainage should be good and it should hold a small amount of water and fertilizer each time they are applied. Water intermediate between sand and clay. Fertilize intermediate between sand and clay.