What type of soil do I have?

IN THIS ARTICLE

Why is soil type important?

The earth’s soil serves as water storage for vegetation (grasses and other plants). If you think of this storage as being similar to a sponge, it helps illustrate why soil type is an important factor in Rachio’s  Smart Cycle feature.
(Soil type is used with Smart Cycle to determine the maximum allowable zone run-time.)

A Simple Illustration

If a sponge gets too dry, it becomes difficult to even begin absorbing water. Similarly, an oversaturated sponge absorbs no water. In both cases, said sponge would allow water to flow right off!

Dry Sponge / Wet Sponge

In the case of your yard, we call this situation "Runoff" – a wasteful (but avoidable) event.

The first step to understanding your lawn lies in knowing what soil consists of - particles, water, & air. The ratios between these three help determine the Soil Type, as entered into the Rachio App. The three basic types of soil are Clay, Loam, and Sand. (more on that later)

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The most reliable way to figure out your specific soil type is with some  simple tests.

How to Test Your Soil

1

Identifying Soil Texture by Measurement | The "Mason Jar Test"

    a
    Spread soil on a newspaper to dry
    • Remove all rocks, trash, roots, etc.
    • Crush lumps and clods.
    • Finely pulverize the soil.
    b
    Fill a tall, slender jar (like a quart canning jar) one-quarter full of soil.
    • Add water until the jar is three-quarters full
    • Add non-foaming dishwasher detergent, about a teaspoon.
    c
    Put on a tight fitting lid and shake hard for 10 to 15 minutes.
    • This shaking breaks apart the soil aggregates and separates the soil into individual mineral particles.
    d
    Set the jar where it will not be disturbed for 2-3 days.
    • Soil particles will settle out according to size.
    • After 1 minute, mark on the jar the depth of the sand.
    • After 2 hours, mark on the jar the depth of the silt.
    e
    When the water clears mark on the jar the clay level.
    • This typically takes 1 to 3 days, but some soils may take weeks.
     f
    Measure the thickness of the sand, silt, and clay layers.
    • Thickness of sand deposit  ____
    • Thickness of silt deposit  ____
    • Thickness of clay deposit   ____
    • Thickness of total deposit  ____
    g
    Calculate the percentage of sand, silt, and clay.
    • [clay thickness] / [total thickness]  =  ___ percent clay
    • [silt thickness] / [total thickness]  =  ___ percent clay
    • [sand thickness] / [total thickness]  =  ___ percent sand
    h
    Turn to the Soil Texture Triangle [Fig. 1] and look up the soil texture class.
    Figure 2. Measuring Soil Texture
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2

Identifying Soil Texture by Feel | the "Hands On" approach

Feel test – Rub some moist soil between fingers.

  • Sand feels gritty.
  • Silt feels smooth.
  • Clays feel sticky.

Ball squeeze test – Squeeze a moistened ball of soil in the hand.

  • Coarse texture soils (sand or loamy sands) break with slight pressure.
  • Medium texture soils (sandy loams and silt loams) stay together but change shape easily.
  • Fine textured soils (clayey or clayey loam) resist breaking.

Ribbon test – Squeeze a moistened ball of soil out between thumb and fingers.

  • Ribbons less than 1”
  • Feels gritty = coarse texture (sandy) soil
  • Not gritty feeling = medium texture soil high in silt
  • Ribbons 1-2”
  • Feels gritty = medium texture soil
  • Not gritty feeling = fine texture soil
  • Ribbons greater than 2” = fine texture (clayey) soil

NOTE

  • A soil with as little as 20% clay will behave as a clayey soil.
  • A soil with 45% to over 60% medium to coarse sand will behave as a sandy soil.
  • In a soil with 20% clay and 80% sand, the soil will behave as a clayey soil.
Also see: Figure 3.  Soil texture by feel flow chart>
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Soil Types, explained

Sand, Silt, and Clay

Texture refers to the size of the particles that make up the soil. The terms sand, silt, and clay refer to relative sizes of the soil particles. Sand, being the larger size of particles, feels gritty. Silt, being moderate in size, has a smooth or floury texture. Clay, being the smaller size of particles, feels sticky. [Figure 4]

Figure 4.  Comparative size of sands, silt and clay. If clay was the size of a dot on the page, silt and sands would be a comparative size.

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Soil types

As mentioned earlier, there are three basic soil classes identified by Rachio; Clay, Sand and Loam:

  • Clay soil is generally heavy and is compact in nature. Plants have a harder time developing roots in clay soil. Clay soil tends to retain water, but this is not always desirable. A clay or heavy clay soil, will greatly benefit from the addition of organic material, and it’s almost impossible to add too much.
  • Sandy soils are the opposite of clay and generally drain too fast, and so are unable to hold onto any nutrients long enough for a plant to use them. Organic matter helps to hold onto water and nutrients, and as with clay, it’s almost impossible to add too much.
  • Loamy soil is a rich, dark and crumbly soil that will allow drainage, but still retain enough moisture to be beneficial. Loam is a good balance of sand, clay, silt and organic matter. If you grab a handful of loamy soil, it should not form a compact ball. It should remain loose and crumbly. Loam is the best type of soil for growing almost everything!

In just the US alone, there is a wide spectrum of soil types, as illustrated below.
US Soil Textures

Consider yourself a bit of a Lawn Geek? ;)

Below are a few resources & interactive maps that can help ID your soil type:

  • USDA Web Soil Survey - pick an Area of Interest (AOI), search available data
  • USDA Soil Surveys by State - available surveys by State & Area/County (Tables / listed data)
  • UCDavis SoilWeb App - zoom to Location, select a region within boundary lines
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  • How To Edit

    >
    For in-app instructions on editing your zones, please see:   How do I set up my zones?
    • The soil types available within the Rachio app, are outlined in Step #3.
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    Figure 1. Soil Texture Triangle
    Soil Texture TriangleThe  soil texture triangle gives names associated with various combinations of sand, silt and clay. A  coarse-textured or  sandy soil is one comprised primarily of medium to coarse size sand particles. A  fine-textured or clayey soil is one dominated by tiny clay particles. Due to the strong physical properties of clay, a soil with only 20% clay particles behaves as sticky, gummy clayey soil. The term  loam refers to a soil with a combination of sand, silt, and clay sized particles. For example, a soil with 30% clay, 50% sand, and 20% silt is called a  sandy clay loam
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    Figure 3. Soil texture by feel flow chart
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