What Is Acidic Soil pH

By testing the pH value of the soil, you can find out whether it is usually acidic or alkaline. For plants to grow well, the pH level needs to be just right. Also, it’s important to know how different ways of managing soil will change the pH of the soil over time. Researchers have found that some farming methods change the pH of the soil in a big way.

What Is Ph?

The pH of the soil tells you how acidic or basic the soil is.

A pH number is actually a way to measure how many hydrogen ions are in a solution. A logarithmic measure (pH) is used because the concentration of hydrogen ions can be very different. For every 1 drop in pH, the acidity goes up by 10.

The pH scale is “backwards,” so very acidic soil has a low pH and a high hydrogen ion content. So, the concentration of hydrogen ions is low when the pH is high (alkaline).

The pH of most soils is between 3.5 and 10. When it rains a lot, the pH of the earth is usually between 5 and 7, but when it doesn’t rain much, it’s between 6.5 and 9.

Soils can be classified according to their pH value:

6.5 to 7.5—neutral above 7.5—alkaline below 6.5—acidic, and soils with a pH of less than 5.5 are very acidic.

Some acid sulfate soils have pH levels that are less than 4, which is very acidic.

What Is Acidic Soil pH


The pH of natural soil is based on the rock that the soil was made from (parent material) and the weathering processes that happened on it over time, space, vegetation, climate, and topography. In the long run, these processes tend to lower pH (make it more acidic).

Some farming actions can also speed up the process of acidification.

What Is Acidic Soil?

There is a range from 1 to 14 that shows how acidic something is, including soil. Anything less than 7 is thought to be acidic. Everything above is thought to be alkaline. A pH level of 6 to 7.5 is good for most yard plants. The best pH range for yard plants is between 6 and 7.5. This is because phosphorus in the soil dissolves in water and is taken up by plant roots at that pH range.

One of the three macronutrients that all plants need is phosphorus. In the NPK ratios that you see on fertilizer packages, phosphorus is the middle number. It helps the plant grow and set fruit.

What Causes Acidic Soil?

It might surprise you as a farmer to find that your garden’s soil is more acidic now than it was the last time you checked. Most of the time, acidic soil is found in nature, even in wooded areas.

This is why many plants that grow in forests, like the native North American ground cover bunchberry (Cornus canadensis), like acidic soil. Over time, the earth can become acidic because of three main things:

  • Chemical fertilizers: Using fertilizers that are high in nitrogen makes the soil more acidic.
  • Heavy rain: When it rains a lot, water moves quickly through the soil, which is called leaching. This takes good things like calcium and magnesium and makes the soil acidic.
  • Organic matter: The ground naturally becomes more acidic as organic matter breaks down, whether it’s in your yard or in the forest.

Different people have different ideas about whether the type of mulch you use in your garden changes the pH of the soil. Gardeners have thought for a long time that pine needles or oak leaves will make the ground under them more acidic than other types of mulch.

Types Of Soil Acidity

Soils are acidic in two different ways. Active acidity is the amount of acidity in the soil that can be measured by pH during a normal soil test. This is the amount of H+ ions found in the soil solution when the earth and water are mixed in a 1:1 ratio.

But not all H+ ions are released into solution right away by the soil. Some of the H+ ions stay tied to clay and organic matter (OM) particles that have negatively charged exchange sites.

This level of acidity is known as “reserve acidity” because H+ can be released into solution when the soil’s solution conditions change because of changes in wetness and the amount of ions and salts that are dissolved. Adding a weak calcium chloride solution (0.01 M CaCl2) or a buffer to the water pH suspension is one way to measure how acidic it is.

Active and reserve acidity, which are shown by water and buffer pH, are connected, but how they work together depends on the types and amounts of clay minerals, organic matter, and free lime in the soil.

The amount and type of clay and organic matter in the soil affects the cation exchange capacity (CEC), which in turn affects the reserve acidity to active acidity ratio. A soil with a high CEC (more OM and clay) can better handle acidity than a soil with a low CEC (more sand, less clay, and more OM).

How To Test Your Soil

Every few years, check the pH level of your soil. You can send a sample of soil to your local extension office and have them do the test for you, or you can do the test yourself. You can get test kits at most home improvement shops and a lot of garden centers. Find out what pH level your plants like in the soil: Before you plant something, you should learn about it so you know which plants do best in acidic or alkaline soil.

How To Make Soil More Or Less Acidic

It is important to keep an eye on the pH level of your soil since it takes time for the pH to change. To change the soil, do the following:

Raising Soil Acidity

Plants that like acidic soil (also known as “acid-loving” plants) can have the soil made more acidic. The pH of the earth drops when you do this. Commercial fertilizers with ammonium-N are the best way to raise acidity. For example, you can find this ingredient in fertilizers made just for azaleas and blueberries.

Lowering Soil Acidity

On the other hand, plants that do better in sweet soil might not do as well in acidic soil. Adding yard lime to your soil will raise its pH, which will make it less acidic. Lime has been used for years to make acidic soils less acidic. The white powder that you might see spread out on a field of crops is lime.

A soil test can tell you if the pH of your soil needs to be raised. If it does, add garden lime to your list of fall lawn and garden care chores. What you did will start to show over the next growth season.