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Improving Your Soil Structure

Improving soil is different from simply adding fertilizer. Although fertilizer contains key nutrients, these are used up fairly quickly, and it won’t do anything for the structure, or long-term fertility of the soil. For that, you need to add organic matter, and it’s worth doing once every year. Late autumn is a good time to prep your beds and borders because the garden is quiet and ready for the winter, but any time from late autumn to early spring will work.

There are a few reliable home tests that you can perform, for determining soil texture. These are important tests, as soil texture measures water movement.

One fun test to do at home is the soil sedimentation test, or Jar Test. You can do this test very simply or do a more clinical analysis. We will talk about a simpler method here. Taking various samples from different parts of your planting areas is recommended.

Needed Materials and Equipment:

  • Quart Glass Jar & Lid
  • Screened & dried soil sample (air dried and sifted through a screen), no clumps, sticks etc.
  • Sharpie & ruler marked in mm
  • A dry detergent; such as Calgon (hexametaphosphate salt powder), to be used as a dispersing agent.
  • Water

Directions:

  1. Fill your jar about 1/3 full with topsoil, add teaspoon of the dispersing agent, and add water until the jar is almost full.
  2. Screw on the lid and shake vigorously, until all the lumps of soil are dissolved. Let the jar settle on the windowsill for 24 hours. Measure that as your soil depth.
  3. Shake the jar thoroughly for 3 – 5 minutes. Set the jar on a windowsill and watch as the larger particles begin to sink to the bottom.
  4. Let the jar settle for 40 seconds to 1 minute. The sand portion of the soil will have settled to the bottom. Mark the level of the sand on the side of the jar.
  5. Leave the jar undisturbed for 2 hours more. The finer silt particles will gradually settle onto the sand. You will find the layers are slightly different colors, indicating various types of silt particles. Mark the level of the silt.
  6. Leave the jar overnight. The next layer above the silt will be clay. Mark the thickness of that layer. On the top of the clay will be a thin layer of organic matter. Some of this organic matter may still be floating in the water. In fact the jar should be murky and full of floating organic sediments.
  7. Use the measurements to calculate the percentage of each soil component by dividing each particle by the total depth of the soil.

At this point there is a more detailed mathematical process you can do to further analyze your levels of different particles. Click here to read more about it.

Not sure what type of soil you have? There are some easy do at-home tests that you can perform to determine what your soil is comprised of! Click here to read more on how to test your soil texture and pH.

SANDY OR ROCKY SOIL:

Sand particles are large, irregularly shaped bits of rock. In a sandy soil, large air spaces between the sand particles allow water to drain very quickly. Nutrients tend to drain away with the water, often before plants have a chance to absorb them. For this reason, sandy soils are usually nutrient-poor.

To improve sandy soil:

  • Select well-decomposed materials, like finished compost, aged manure, peat or coconut coir. Organic matter in the form of composted manure, chopped up leaves, green manures, or vermi-compost will also improve the texture and water-holding capacity of your soil.
  • Work in 3 to 4 inches of organic matter to your soil.
  • Mulch around your plants with leaves, wood chips, bark, hay or straw. Mulch retains moisture and cools the soil.
  • Add at least 2 inches of organic matter each year.
  • Grow cover crops or green manures.

Use a combination of these materials for quick improvements that last.

CLAY SOIL:

Clay particles are small and flat. They tend to pack together so tightly that there is hardly any pore space at all. When clay soils are wet, they are sticky and practically unworkable. They drain slowly and can stay waterlogged well into the spring. Once they finally dry out, they often become hard and cloddy, and the surface cracks into flat plates.

Lack of pore space means that clay soils are generally low in both organic matter and microbial activity. Plant roots are stunted because it is too hard for them to push their way through the soil. Foot traffic and garden equipment can cause compaction problems. Fortunately, most clay soils are rich in minerals, which will become available to your plants once you improve the texture of the soil.

To improve clay soil:

  • Work 2 to 3 inches of organic matter into the surface of the soil. Then add at least 1 inch more each year after that.
  • Add the organic matter in the fall, if possible.
  • Use permanent raised beds to improve drainage and keep foot traffic out of the growing area.
  • Minimize tilling and spading.

SILTY SOIL:

Silty soils contain small irregularly shaped particles of weathered rock, which means they are usually quite dense and have relatively small pore spaces and poor drainage. They tend to be more fertile than either sandy or clay soils.

To improve silty soil:

  • Add at least 1 inch of organic matter each year.
  • Concentrate on the top few inches of soil to avoid surface crusting.
  • Avoid soil compaction by refraining from unnecessary tilling and walking on garden beds.
  • Consider constructing raised beds.

2 thoughts on “Improving Your Soil Structure

  1. You don’t include any information about what percentages of sand, clay and silt are found in healthy soil, or in Colorado soils. What should we measure our percentages against, in order to know whether we have sandy, clay or silty soil?

    1. Healthy or not healthy, your soil is your soil. There are some easy at-home tests you can perform to “generally” decide what your soil type is. Click here to read more about the different DIY tests you can use to determine what type of soil you have. Then if your soil is comprised of clay, add larger size particles to improve it, and if your soil is gravel or larger size particles, then improve it with organic matter. To have an exact measurement of what your soil is composed of, you can have CSU Soil Testing Labs do an analysis for you. They will give you exactly what you need by proportions to improve your soil structure for whatever your needs are.

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