Performing a Soil Test to Determine the Soil Type

Testing the Soil Type

I have often found myself looking at gardening magazines and watching gardening shows and wondering: Why is my garden not performing as well as the gardening show says or as the gardening magazines claims it will be doing? The picture that I get from my garden does not even remotely resemble the pictures in the gardening magazine even if I followed all instructions to the tee. If I am lucky there might be a minute version of the plants pictured in the magazine of gardening show. Sometimes the suspicion of disease or pests might be evident, or sometimes even the thought that maybe the plants were planted in the wrong spot.

Do these gardening questions sound familiar? Well in my case this was certainly the case. Seldom did it ever occur to me that the soil could be at fault. Different types of soil are suited to different types of gardening. It seems pretty obvious, doesn’t it? Now this brings me to another dilemma? How can one tell that the soil is at fault? – The solution would be to perform a soil test to make sure what soil type you have in your home garden. When it concerns soil and soil types and soil amendments, and types of fertilizers, there are many factors that affects the way in which plants will grow in a garden. What is the answer: Do I need to change all my garden soil or can I save my garden soil? Fortunately most of these factors can be measured and consequently the test results or measured results will indicate what could be wrong and right in some cases.

A quick soil test will help you work out what soil amendments are necessary to make your plants grow better. If you happen to have garden soil that is in need of serious soil amendments then you will find that it might be necessary for repeated soil testing, at least until you achieve the required soil type. Repeated soil testing should be carried out every few months to be able to see and gauge how well the garden soil has been changed.

A soil test is quite simple and you do not need much to perform it. In fact all that you may require would be the following:

The soil triangle


  • A large, straight sided glass bottle or jar with a tight fitting lid.
  • One (1) teaspoon of washing powder.
  • A ruler or measuring stick.
  • A calculator.
  • A soil sample.
  • The soil triangle.

The soil test procedure

Collecting the soil sample

The first thing you need is a soil sample but How much garden soil constitutes a sample? It is best to take one or two cups of garden soil. This sample of garden soil should be taken from the middle of the garden bed that you wish to test.

  • What about the size of my garden? Depending on the size of the area of the garden soil that you want to test; if it is a large area, collect smaller samples from various spots are regular intervals and make up a composite sample of garden soil to test.
  • What is an accurate garden soil sample? You need to collect your garden soil sample from the root zone. This can be done by digging down into the bed and taking the soil sample from below 10 cm (3 to 3.5 inches).
  • What should be included in the garden soil sample? You should leave most of the particles in your garden soil sample except for the stones and ‘foreign’ objects.
  • What do I do with the soil sample? Place your garden soil sample in a plastic bag and do not forget to label the bags if you are collecting more than one sample.

Preparing the soil sample

Now that you have collected your garden soil sample, you can proceed to spread the soil sample out in a beer box and leave it in the sun to dry for a day. (TIP: You can also dry the garden soil sample in a warm oven.)

  • Sift the soil to remove smaller stones and roots from the soil sample. The sifting will also break down lumps.
  • Place enough sifted garden soil in the jar to fill it halfway.
  • Add the washing powder.
  • Fill the jar with water.
  • Close the jar tightly and shake the garden soil sample, washing powder and water for a minute or two to combine the soap, soil and water. (The soap acts as a surfactant. A surfactant will keep the soil particles separate which will yield a more accurate test result.)
  • Put the jar on a level surface and allow the sediment to settle.

You will notice that as the garden soil in the jar settles, the largest particles will settle first. (This is usually the sand.)

The next level of sediment that will settle is the silt. Silt is usually darker than the sand particles.

It will take a day or two for the clay, which is the next level of sediment, to settle. The clay is the finest particles in the garden soil. Clay is usually lighter in color than silt.

Measuring the layers of sediment

Now that your prepared garden soil sample has completely settled, you should measure the soil mass using the ruler or measuring stick. The complete measurement represents 100% of the garden soil sample.

Now you need to derive the percentages of sand, silt and clay in the garden soil sample. This can be done my measuring the amount of each of these players of sediment. Then divide it by the amount of the total sample, and then multiply the resulting figure by 100.

Once you have all the percentages of each layer of sediment or each particle of the garden soil sample, transfer the results onto the soil triangle then you will be able to determine what type of garden soil you have.

How to diagnose the fertilizer needs of your garden soil

Once you have determined what type of soil your garden has, then the next logical step would be to diagnose the fertilizer needs. There are basically four different types of tests that can be conducted to determine the fertilizer, i.e. type of fertilizer and quantity, requirements of you garden soil. These tests are field tests, pot tests, biological tests and chemical tests. Of these tests, the field tests are the most reliable, but involve a lot of time and can be quite expensive. The pot tests can be done within a limited amount of space and in a much shorter time than the field tests. However, the results may not always be helpful as the conditions of these tests are different from those in the field. The biological tests involves the growing of seedlings and other plants forms like fungi and even bacteria under specified conditions and the subsequent study of their relative growth and the content of needed nutrients. It is a slow and very expensive method of testing that has to be carried out periodically. This is not a very practical test for a home gardener to conduct. And then there is the chemical test which involves the chemical analysis of the garden soil. A chemical analysis of your soil will provide you, the gardener with information on the relative abundance or scarcity of the different types of nutrients in the soil. (TIP: Remember this chemical analysis will not provide you with the exact quantities of fertilizer that may be required to remedy your soil nutrient deficiency.) The chemical test dependability can however be improved when used in conjunction with field tests.


Fortunately for the home gardener, there are many rapid soil testing facilities and equipment available these days from garden centers, nurseries and even some hardware stores. Often one can get a clue of the nutrient deficiencies that prevail by watching the symptoms as it is manifested in the plants that you cultivate in your garden.

However, the correct diagnosis of deficiency symptoms comes after experience. The more we tinker and toil in our gardens the more we will get to know and understand our soil, soil type and fertilizer needs.

How to make soil amendments

Following up on determining what type of soil and the fertilizer needs you have in your garden, it might be necessary to make the necessary amendments so as to achieve better results in your garden. Ideally the best garden soil would be either a loamy soil or a clay loamy soil. It is thus obvious that one would try to amend one’s soil towards the ideal.

Garden soil leaning towards the sandy soil side

You will need to add some clay OR at least some loamy soil to get a more balanced texture in your soil.

While adding compost may temporarily add a loamy texture to your garden soil, it will break down after time. This means that you will have to add compost to your garden beds on a regular basis so that your plants can derive the full benefit.

If you can add clay soil to your garden beds always take care not to add too much clay at a time. Clay soil has the tendency to clog together and when you do add the clay soil to your garden bed make sure to incorporate the clay well into the bed. Unblended sections of clay will clog together.

Garden soil leaning towards the clay side

It is easier to amend clay coil. In most cases you will need to amend your soil by adding plenty of organic material. Organic materials such as compost, bark chips, fine milled bark, vermiculite and river sand will break up the clay soil.

In worst cases then agricultural lime will help to break down clay soil and prevent the garden soil from becoming sticky when water comes in contact with the soil.

Garden soil leaning towards the silt side

Silt soil is also easy to amend. All that would be required to carry out silt soil amendments would be to add plenty of compost and this will result in lovely friable soil – ideal for most plants.

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