How to Adjust Soil pH

Two Methods:Increase the pHDecrease the pH

A soil's pH represents how acidic or alkaline your soil is, based on a scale from 0 to 14. A neutral pH is 7. Anything over 7 is considered alkaline and anything below 7 is considered acidic. A plant's preferred pH level varies for each plant, and is important because it affects how efficiently the plant absorbs nutrients. Understanding how to adjust soil pH first starts with testing your soil so you know where it lies in the number scale. From there, you add ingredients to adjust the pH to the proper level.

Method 1
Increase the pH

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    Add a lime source to make the soil less acidic. The carbonate ion in lime sources works to neutralize the acid.
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    Select your lime source depending on the needs of your plant. Some lime sources contain micronutrients like dolomite, which is a mixture of calcium and magnesium carbonates. Wood ashes also provide lime with the addition of other micronutrients including potassium, phosphate, boron and other elements. Standard lime comes in 4 types of ground limestone forms: pulverized, hydrated, granules and pellets.
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    Apply the liming source 2 to 3 months before planting (usually in the fall or winter) so there is plenty of time for the pH to change.
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    Mix the lime thoroughly into the soil because most liming sources are not very water-soluble.
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    Water the soil regularly after adding the lime. Water activates the lime source to reduce acidity.

Method 2
Decrease the pH

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    Add sulfur or aluminum sulfate to the soil to make it more acidic. Both supplements are found at most garden supply stores.
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    Make an immediate decrease in the soil pH by adding aluminum sulfate, which produces instant acidity due to the aluminum content.
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    Increase the soil's acidity slowly by using sulfur. Sulfur works in conjunction with the soil's moisture, temperature and bacteria to lower the soil pH.
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    Aggregate the sulfur or aluminum sulfate into the soil thoroughly.
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    Wash the sulfur or aluminum sulfate off any plant leaves that it comes in contact with to avoid burning the plant.


  • Reducing the pH in naturally alkaline or calcareous soils is difficult and sometimes impossible. If this is the case with your soil, plant flowers and shrubs that will thrive in alkaline soils.
  • When it comes to limestone forms, the finer the limestone, the easier it is absorbed into the soil and the faster it changes the pH.
  • Wood ashes are not as effective a lime source as limestone but with repeated use, it can raise the soil pH immensely.

Things You'll Need

  • Soil test
  • Water
  • Lime source
  • Sulfur or aluminum sulfate

Sources and Citations

Article Info

Categories: Soil Chemistry