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How to check your soil

by Drucilla James

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We all invest a great deal of money and time in the plants that we buy, but sometimes we ignore the most vital thing that will bring success- that is the soil into which we plant our treasures. The soil is the most important element in the garden and must be right to achieve the best results from what we grow.

You need to know what type of soil you have, its pH and any mineral deficiency that may exist.

What is soil?

The bulk of soil is made up of rock and mineral particles mixed with varying amounts of organic matter; the remainder is air spaces, water and mineral elements (nutrients). Roots take up water, oxygen from the air spaces in the soil and nutrients (absorption is affected by pH) which are essential to the growth and health of the plant.

Step-by-step

Step 1: Identify your soil type

There are six main soil types. The easiest way to check what type you have is to pick up a sample of soil that is damp and to look carefully at what it is made up of. Rub it between your fingers and check your observations against the following table.

OBSERVATIONS SOIL TYPE FEATURES ACTION
Brown with crumbly structure. LOAM Mixture of clay, sand and silt, easily worked, well drained and fertile. Add organic matter regularly.
Shallow soil, lumps of chalk and or flint. CHALK- lime rich Can be difficult to cultivate. Drains very quickly and is always very alkaline. Choose appropriate plants.
Heavy soil, sticky to handle, easily rolled into a ball. CLAY Bakes dry and hard in summer so surface cracks. Takes longer to warm up. During winter becomes waterlogged as it retains water and drains slowly. Hard to cultivate. Potentially very fertile. Break up with the addition of organic material.
Fine grain soil with silky feel. More easily compacted than sandy soil. SILTY Fairly well-drained and fertile. Add organic material.
Spongy to the touch and does not clump easily. PEATY Black acid soils. Mainly organic material and very fertile. Good moisture retention. Usually farmland hardly ever found in gardens. Rare in gardens- rejoice if you have it.
Feels rough and gritty and difficult to compress into any shape. SANDY High in sand so light soil and easy to cultivate, free draining. Warms up quickly and dries out quickly. Low in nutrients as easily leached out. Usually acidic. Add lots of organic material supported by addition of fertiliser.

 

Step 2: Identify the pH-how acid or alkaline the soil is

pH is very important because it has a major impact on the plant’s ability to take up nutrients and most operate best at pH 6.5 to 7.

Before growing or buying plants, measure the pH of your soil and check that the plants you want to grow will flourish there.

Method 1:  Soil-testing kits

These are readily available from garden centres, inexpensive to buy (£3 to £9), easy to use and reasonably accurate. They rely on colour judged against a colour chart.

  • Remove the upper 5cms of soil from the test area, break up the next 10cms of soil now exposed.
  • Take a small soil sample from the area (clear it of any debris and stones) and dry it naturally. When dry put some in the test tube provided to the 1 ml mark.
  • Add a spoonful of white barium sulphate powder from the kit to the dry soil.
  • Add the pH test solution to the 2.5 ml mark as directed by the instructions.
  • Cap the tube and shake,then leave the contents to settle. If the solution takes too long to settle add another spoonful of barium sulphate, shake and leave to settle again.
  • Match the resulting colour against the chart in the kit.

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The pH of your soil may vary at different places in your garden so test each area in which you intend to plant.

Interpreting the colours

  • Yellow-orange/red indicates acid pH 3 to 6 (below 5 is classed as very acid).
  • Green indicates neutral pH 7.
  • Dark green to blue indicates alkaline pH 7 to 9.

The soil can also be easily tested to identify free calcium carbonate (chalk/limestone) by adding vinegar (acid) to a sample which if it then fizzes shows calcium carbonate is present.

Lime can be added to increase pH and acidifying materials such as sulphur and iron sulphate can be added to lower the pH.

Some kits also come with the materials that will enable you to measure the levels of important nutrients (nitrates, phosphorous and potassium) in your soil (£25 from most garden centres).

Method 2: pH meter

These simple to use machines are small, give quite accurate results (though some people feel they are not as accurate as the chemical colour indicator test) and are inexpensive (about £9 with a moisture meter attached).

The probe has simply to be inserted into the soil and a pH reading will come up on the screen when the needle has settled. It is advisable to repeat the process a number of times. Make sure you clean the tip of the probe before each reading.

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Method 3:  Call in the experts

The most accurate results are obtained by sending a sample or samples to the RHS (their service has been designed for gardeners) who will do an analysis of soil texture, pH, organic matter and the three major nutrients (potassium, phosphorous and magnesium) and give you a report as to the action you should take. There is a fee of £25 for RHS members and £30 for non-members.

How often should you test your soil? Keen gardeners do it once a year, however do not test the soil for three months after adding any material (fertiliser, compost, sulphur or lime) to it as this will give an inaccurate reading.

One Response to “How to check your soil”

  1. Ros

    Excellent information, thank you!!

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