pH Of Potting Soil: Explained In Simple Way


pH of the soil is a measurement of alkalinity or acidity of the soil in pH units. pH stand for potential hydrogen. It is the measurement of number of hydrogen ions present in the soil and it is determined on a scale that moves from 0 to 14.

0 Most Acidic
7 Neutral
14 Most Basic

The pH scale is a logarithmic scale that means each increment is 10 fold increment.

Soil with pH value 3 is more acidic than the soil with pH value 4.

If the pH value is between 7 to 0 then the acidity increases.
If the pH value is between 7 to 14 then the basicity increases.

Effect Of Soil pH On Plant Growth

  • pH of the soil determines the access of nutrients by the plants.
  • Soil becomes acidic when basic nutrients like magnesium, calcium etc. are replaced by hydrogen ions.

Soil Test Procedure

It takes less than 60 seconds to determine the pH of the soil.

pH Meter

Measure Your Soil pH with pH Meter
  • Simply place pH meter in slightly wet soil and wait for a while so that the needle shows the suitable reading on the pH scale.

pH Testing Kit

Measure Your Soil pH With Testing Kit
  • Testing kits are also available to determine the pH of your soil. With this kit you will get test tubes and capsules.
  • Simply add specified amount of soil, one testing capsule and distilled water in test tube.
  • Shake the test tube and observe that the color of the water changes and specifies the pH value.

Which is the best method?

  • Both methods are affordable and helps in determining the needs of your soil, which indirectly determines your plant growth.

Effect of pH:

  • Even though you have taken a proper care on your garden there may be a chance of change in pH levels.
  • Both higher and lower pH levels results in toxic vegetables.
  • Most plants grow under the pH value of 6-7.

Factors Affecting Soil pH


  • Rainwater combines with carbon dioxide to form carbonic acid. Later carbonic acid ionizes into hydrogen and bicarbonate ions.
  • These hydrogen ions replaces the calcium, magnesium and sodium  present in the soil.
  • The displaced sodium or magnesium or calcium ions combines with bicarbonate ions to form sodium bicarbonate or magnesium bicarbonate or calcium bicarbonate and gets washed away.
  • The left over hydrogen ions increases the acidity of the soil .
  • So in this way rain water drains out magnesium, calcium, sodium and potassium from soil.
  • The areas that doesn’t receive enough rain fall will tend to have slightly alkaline soil.
  • Whereas areas that receive high rain fall will tend to have acidic soil.


  • Plants cannot use atmospheric nitrogen for their growth.
  • Nitrogen is indirectly supplied through urea and nitrogen fertilizers. The ground bacteria breaks the ammonia present in urea and nitrogen fertilizers into nitrates.
  • The left over hydrogen ions combines with calcium or sodium or magnesium causing both nutrition deficiency and increase in the acidity of the soil.
  • Intensive cultivation, too much usage of urea and ammonia makes soil acidic. You should use them in required quantity.
  • Use lime after the usage of nitrogen fertilizers to bring down the acidity.

Organic matter:

  • To form organic acids, organic matter present in the soil gets decomposed and mixed up with ground water.
  • These acids elevates acidity in soil.


  • Legumes indirectly elevates the acidity of the soil.
  • They absorb more cations (H+) when compared with anions.
  • To maintain stability between ions in their cells, they discharge cations (H+) and increase the acidity of soil.


  • It resist the changes in soil pH.
  • Compost has noticeably positive change when it is added to acidic soil.
  • Ensure that you have added all the necessary micro nutrients to the compost.


  • Lime assists in elevating the soil pH.
  • It is cost effective, mild to handle and will not show any negative effects on soil.
  • It decreases the amount of hydrogen ions in soil.
  • Calcium ions in the lime replaces the hydrogen ions in soil.
  • So, there is a decrease in the acidity and increase in the nutrients like calcium, magnesium etc. in soil.
  • Sometimes, the top most layer of the soil is neutral, the sub soil layer may be acidic and halts the plant growth. So, lime stone should be deposited in sub soil layer.
  • Its better to use dolomite lime. It helps in adding both calcium and magnesium to the soil.


  • Sulfur is cheap, harmless to the plants and best suited for containers.
  • It reacts with atmospheric oxygen and forms sulfuric acid which helps turning the soil into acidic.
  • Sulfur helps in bringing down the pH level.
  • For faster results use sulfur powder instead of using sulfur chips.
  • The amount of sulfur to be added depends on the type of the soil. The soil which is rich in clay and organic matter needs more sulfur to neutralize.
  • Add small amounts of sulfur since larger quantity kills the plant.
  • Ensure that the wind should not blow up the sulfur powder that you have applied on the surface of soil.
  • When you are applying sulfur to large number of containers make sure that you use goggles, mask and gloves.


  • Adding iron to the soil decreases the yellowishness of leaf.
  • But adding iron sulfates reduces pH and interferes with phosphorus levels.

Aluminium Sulfate

  • Aluminium sulfate rapidly brings down the pH of soil.
  • When used in large quantity it interfere with phosphate level and increases the aluminium level which is toxic to the plants.
  • If your soil is rich in lime or chalk then you cannot acidify it. So, add vinegar to your soil sample. It reacts with the calcium carbonate in the soil and forms bubbles.

Municipal Water:

  • Tap water contain salts and increases the pH of your soil.
  • Check the pH of the soil regularly to maintain it.


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