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Soil Texture

By Wayne Jewell

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In past articles, you may have read where I have used the expression a “loam or loamy soil”.    A friend of mine asked me not too long ago “What is a loam soil”?   My response was:  “I am glad that you asked that question.”

My Oxford Dictionary defines it as “a rich soil.” A clay soil is often a rich soil too. Rich in minerals and nutrients that are so tightly bound to the soil particles that they are not readily available to plants.

I think a better definition of a “loam soil” would be that it is one of several soil textural classes that is rich in nutrients, drains readily but still retains enough moisture and has readily available nutrients for plant growth. In other words, one of the most ideal garden soils.  

A soil is made up of particles of various sizes. The largest particles (not including actual stones) would be sand, followed by smaller particles called silt and the smallest particles called clay.  The percentage of each of these three particle sizes in a particular soil determines a soil’s textural classification. For example, a soil might be a loam, silt loam, silt clay loam, sand, clay, etc.  In all, there are 12 different soil texture classifications.

The United States Department of Agriculture came up with what is referred to as a soil textural triangle. (See fig. 1) One side lists the percentages of sand, one side percentages of silt and the third side the percentages of clay in a given soil. By looking on this triangle to see where each of these 3 percentages intersect, you can determine what soil texture is in your garden soil.

Of course, before you do this, you must first find the percentages of sand, silt and clay in your soil.   To do this, you take a sample of soil from your garden. It is best if you take several samples from the top 4 to 6 inches of soil and make up what is called a “composite sample”.  Mix this soil all together and add enough to mason or pickle jar to make it about ¾ full of soil. Then, add enough water to fill the jar to the top. Cap it and proceed to shake it up for a few minutes and then let Page 2   of 3 it settle for about an hour.  You will notice that they soil will settle out in layers.

The sand will settle to the bottom first, followed by the next layer which will be silt and finally the top layer will be clay.  If you take a ruler and measure the size of each layer and then divide that by the total size of all of the soil, you will come up with a percentage for each particle layer.  For example, let’s say that in this jar, we have 6 total inches of soil. After everything settles, we have a 3-inch layer of sand, a 2 inch layer of silt and a 1 inch layer of clay, we would have a soil that is 50 percent sand, 33 percent silt and 17 percent clay.   Looking on the soil texture triangle, we would find that we have a soil that would be in to the texture class called loam.  By comparison, let’s say that the percentages came out percent sand 17, percent clay 33 and percent silt 50, we would then have what is called a “silty clay loam”. If you have a soil that falls in to any of the categories that have the word loam in them, you should be fine for your vegetable or flower garden.  Some gardeners will actually add sand or clay to their gardens to try to change the texture.  Keep in mind that they make cement out of certain types of clay and they add sand to cement to make it harder.

Your best bet is to add composted organic matter if you want to improve the soil you have on hand and call it a day.

So, in response, my friend replied: “Wow, I am sorry I asked”.   I laughed and said “yes, maybe you should stick to shopping."

fig. 1: United States Department of Agriculture Soil Texture Class Triangle