The Dirt on Dirt: Sand, Silt, Clay, and Loam

Photo courtesy of freedigitalphotos.net

Photo courtesy of freedigitalphotos.net

One of earth’s most vital and under-appreciated resources is sitting beneath your feet right now…dirt! Dirt is actually an amazing substance if you think about it. Millions of years in the making, it gives rise to most plants and by extension most animals, and it is 100% necessary for life as we know it. Soil sustains our ecosystems, grows our food, is integral in the production of the very oxygen we breathe, and yet it gets no respect. Kicked by baseball players, methodically cleansed from our homes, clothing, and hands- we have clearly lost touch with dirt. Dirt is much more complex than you may have been led to believe. Soil is the amalgamation of rocks, minerals, and organic matter, acted upon by the forces of gravity, geologic pressure, weather, and time. So let’s take a minute to learn more about the soil living beneath our feet and give dirt its minute in the sun!

Soil is made up of many small particles. The size and relative ratio of these particles are known as your soil’s texture. There are three general categories of particle size when discussing soil: sand, silt, and clay. Sand particle sizes range from 2.0 to 0.05 mm, silt particle sizes range from 0.05 mm to 0.002 mm, and clay particle sizes are any particle smaller than 0.002 mm. The composition of most soils is usually a mixture of sand, silt, and clay. The ratio of these particles in your soil will have a profound effect on how your plants grow. Finer soils tend to have a greater ability to store soil minerals but also leach those minerals at a faster rate. An ideal garden soil has a mixture of all three particle sizes and is referred to as a loam. This soil (loam) has the best ability to absorb moisture, allow for proper drainage, and transport air; and due to its high content of organic matter, it provides a lasting source of nutrition. Conversely the most difficult soil type to work with is a compacted soil high in clay. It prohibits root growth, struggles to absorb moisture, and doesn’t allow enough air to the roots.

Soil Triangle

Soil Triangle

If you have difficulty growing plants in your native soil or are curious to see what type of soil you have at your home or farm, consider getting it tested at a professional laboratory or agricultural extension. You can also try performing this simple test at home; although not as good as a professional test, it will provide you with a general idea of your soil texture.

All it takes is a clean, empty jar with a lid, some clean water, a tablespoon of detergent and a sample of the soil you want to test. To do so:

  1. Fill the jar about 1/3 full with the soil to be tested.
  2. Fill the jar with water and detergent then cap it.
  3. Shake the jar vigorously and set aside for several hours or overnight.

How to determine your results:

  • If the water is clear and the soil has settled to the bottom; you have predominantly sand soil.
  • If the water is still a little murky with bits of matter suspended in it; you have loam soil.
  • If the water is still murky and there is a visible ring of sediment around the jar; then your soil is mostly clay.
Soil Type Jar Test

Soil Type Jar Test

If you find you are blessed with a rich, nutritious, well-draining, loamy soil, then count your blessings. However, if you are not as fortunate and find that you have sandy soil, the best amendments are ones that increase the ability of the sandy soil to retain water and increase its nutritional content. Amending sandy soil with well rotted manure or compost (including grass clippings, humus and leaf mold) will help to improve the soil the fastest. You can also add vermiculite or peat as sandy soil amendments, but these amendments will only add to the soil’s ability to hold on to water and will not add much nutrient value. If you have clay soil, then it is most important to add organic matter (including grass clippings, humus and leaf mold), but also adding sharp sand followed by either aerating or turning your soil will help improve the compactness of clays. Lastly, adding a healthy layer of wood chip mulch each year will help improve the soil as it decays. Clay soil is not one that can be fixed immediately, but with a little diligence and a few years (and lots of compost), you too will have great soil.

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