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13 April, 2014

How To Take A Soil Sample and Read The Soil Triangle



Taking soil samples for any kind of garden analysis should be done in a manner that will net you the results you need to make your garden more congenial to that part of the plant that lives in the soil – the roots. Roots for most of the plants in our gardens, live about 4 to 18 inches beneath the surface of the soil. Exceptions to this include most drought resistant plants (with roots that range some distance out and down) and other notoriously strong rooted plant – mention just about any weed and it will fall into that category. You want to take your sample around nine inches down. This method of taking a soil sample is effective for the soil triangle tests and is the preferred technique for soil samples sent to labs for testing.


  • Remove as much surface organic matter as possible before taking your soil sample.
  • Put approximately one cup of soil into a straight-sided quart jar with lid.
  • Add approximately one tablespoon of alum or Calgon bath beads – this is a surfactant to help the particles separate from one another.
  • Fill the jar with water almost to the top.
  • Shake vigorously for several minutes to get all the soil moistened. 
  • Let the jar stand undisturbed for at least one hour, separation continues for as long as 24 hours with some soils.
  • The soil mix will separate into layers. The longer it sits, the more distinct the layers will appear.
    Figure out the percentages of sand, silt, clay, and organic matter in the water – do not measure the water itself. The sand will be the bottom layer. Silt will be the next layer, followed by clay; the combination of these three should add up to 100%. Organic matter will float on top of the water and does not figure in the total of percentages..  
    Determine soil type by comparing percentages with soil triangle.
    Understanding soil type will help you know how to properly amend, fertilize, water, and plant so that you will have healthy, disease-resistant, and pest-resistant plants.

    What to do and How to do it

    Follow these steps to determine the name of your soil texture:

    1.Place the edge of a ruler at the point along the base of the triangle that represents the percent of sand in your sample. Position the ruler on or parallel to the lines which slant toward the base of the triangle.

    2.Place the edge of a second ruler at the point along the right side of the triangle that represents the percent of silt in your sample. Position the ruler on or parallel to the lines which slant toward the base of the triangle.

    3.Place the point of a pencil or water soluble marker at the point where the two rulers meet. Place the top edge of one of the rulers on the mark, and hold the ruler parallel to the horizontal lines. The number on the left should be the percent of clay in the sample.

    4.The descriptive name of the soil sample is written in the shaded area where the mark is located. If the mark should fall directly on a line between two descriptions, record both names.

    Feel the texture of a moist soil sample between your fingers.
    Sand will feel "gritty", while silt will feel like powder or flour.
    Clay will feel "sticky" and hard to squeeze, and will probably stick to your hand.
    Looking at the textural triangle, try to estimate how much sand, silt, or clay is in the sample.
    Find the name of the texture to which this soil corresponds; that will be the descriptive name of your soil.
david

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