Soil Composition Analysis
Drainage & Jar Tests
Garden Tip
TB1468
Technical Bulletin Series
The Importance and characteristics of Soil!

All soil is generally comprised of particles that fall into three groups. The smallest is clay, then silt and the largest is sand. Clay compared to sand is as small as a baseball is to the White House. Clay tends to drain very slowly while sand drains too fast. Good "soil" has a mixture of these that will allow for adequate oxygen throughout, but also retain water long enough to prevent plant drought. This is why "silt" is so nice, as a medium sized particle it has the best of both worlds. 40 % sand, 40 % silt and 20% clay makes a nice loamy soil.
Soil Drainage Tests

By performing a "Drain Test" on your soil you can arrive at a good estimate of the type of soil composition that you have. Though Jar Tests can be more accurate, many people prefer the simplicity of simply digging a hole - filling it with water - letting it drain - filling it again, and time how long it takes to drain. There are two methods for doing this:
Quick Drain (I recommend this)
and the 24 hour Drain.
By clicking you will be directed to a page for instructions.

If you would like more accuracy and know the percent
each of these particles comprise of your soil,
try doing
A Jar Test
Instructions follow

Put enough dirt from your planting area in a quart size jar so that the level of the jar is about 2/3 full. Then add water until nearly full. Measuring begins in only 6 seconds. Use a Magic Marker (writes on glass) to indicate settlement points.

The visual striations are not always distinct, like drawings and photos usually indicate. This is the reason for utilizing "TIME" to determine the marking for separation of larger and smaller soil particles.

Measuring based on TIME of SETTLING, uses the inclination of larger particles to settle out, while smaller ones are still afloat. After shaking, quickly set the jar on a table so you can Mark settling points. First measurement is at ONLY 6 seconds, so have the Marker ready to go.

Most sand will settle (6 seconds) to the bottom. The silt (in 20 more seconds) and clay will settle (in 5 minutes or more) on top of that. You will Mark then later Measure the depth point for each and calculate the percentage. In this example we have approximately 7% clay, 20% silt and 73% sand. This is a "sandy loam" and will exhibit excellent mostly rapid drainage. Not a common soil here.
At 6 seconds: Use a MARKER and MARK THIS POINT!
This represents the amount of SAND in the sample.
(in this example 5.5 inches)

Now let settle for only 20 additional seconds


At 26 seconds from start: Again use the MARKER and "MARK THIS POINT!"
this represents the amount of
SILT + SAND in the sample.
(in this example 7.0 inches)

Now let settle for 5 minutes (minimum) from start!

At 5 minutes: Again use the MARKER and "MARK THIS POINT!"
this represents the amount TOTAL SEDIMENT in the sample.

You may want to "re-shake" and measure again.
First measure your original Marks.
Make new marks, and compare with your first measurement
as it is not always clear where the sediment lines actually are.

Organic matter (like compost) will mostly float. The percent of compost can't be measured with the jar test. It can however, be measured by a soil laboratory. A bit complicated and expensive. Unless you have added it, organic material is nearly non-existent in our desert soil.

Now simply use the "Soil Triangle to find your Soil Type.

In order to use the Soil Triangle for determining which classification of soil you have;
You'll need to convert the above measurements in to percentage. Conversion formulas:

for Sand: Sand (inches) divided by Total (inches) = % Sand
for Silt: [Silt + Sand (inches) minus Sand (inches) ] divided by Total (inches) = % Silt
for Clay: [Total (inches) - Silt + Sand (inches)] divided by Total (inches) = % Clay

If this seems a bit difficult, confusing or complex;
You may want to utilize
Planting Guru's
Jar Test Analyser

To use our ON-LINE Soil Composition Analyser to easily convert
your jar test measurements to percentages; click here:

Soil characteristics directly affect proper watering and fertilization.
In fact; without knowledge of the type of soil being watered
IT IS NOT POSSIBLE to provide accurate recommendations for watering.
Any watering schedule offered without knowledge of your soil type is really just guessing!