Clay Soil pH: Is Clay Soil Acidic or Alkaline? 

Today’s hot topic – is soil, not sandy soil, loamy soil, but specifically clay type of soil and if it’s alkaline or acidic. 

I’m often quick to blame horrendous plant diseases for poor plant health in my garden, but the problem in most of these cases is that my soil pH is out of whack or that I’m growing the wrong plants in clay soil. 

Through many years of evolution, certain plant species including those in your garden beds and vegetable garden have grown to like certain soil types such as acidic soil and alkaline soil.

This can be a good and bad thing because it restricts them from growing in specific locations or gives them a competitive advantage as there will be fewer plants competing for fertilizer, water, organic materials, and most importantly space. 

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What is Soil pH?

Whether you’re a novice or seasoned gardener, you’ve probably heard about soil pH, but what exactly is it and why does it matter? 

pH abbreviation for (potential Hydrogen) is the measure of the hydrogen-ion concentration in the soil or other substances.

Since we’re speaking about gardening, it’s enough to know whether your soil is alkaline or acidic. 

The pH scale runs from 0 – 14 units where a pH of 7 is considered neutral and the acidity gets higher as the numbers decrease below 7. 

Soil ph is often overlooked by many gardeners, but can have indirect, yet far-reaching effects on plant growth and overall plant health. Soil pH that’s in an unacceptable range can cause the yellowing of leaves, which indicates an iron deficiency and in worse cases plant poisoning. 

Most plants thrive in somewhat a neutral pH between 6.2 and 7.0, but there are a wide range of other plants that prefer very acidic soil such as azaleas and blueberries, and plants that grow well in alkaline soil include lilacs and clematis. 

There are a few ways to test your soil pH to determine whether it’s in the acidic range or alkaline range such as by sending a soil sample to the lab and at home with vinegar and baking soda. There are a few reasons why soil testing is important.

See also my roundup of the best soil pH testers.

checking clay soil ph level

What is Clay Soil? 

Clay soils are tightly packed old soils that comprise very fine mineral particles and not much organic material.

They are prevalent across the world including the United States and are quite sticky given that there’s not much space between the mineral particles. 

Clay soils offer poor drainage and one way to identify clay soils in your garden is by looking for water that sits around rather than soaking in. 

According to the Department of Agriculture, clay soil is defined as 40 to 100 percent clay. 

Advantages and Disadvantages of Clay Soil

When it comes to clay soil, there’s good news and bad news! Getting to the bad news first – clay coil is difficult to work with because it’s so dense and sticky. Adding to this, clay soil is squeezed together so it blocks the air channels plants and microbes need to survive, resulting in poor drainage conditions.

But even though clay soil has received a bad rep, there are many advantages of this type of soil.

Advantages of Clay Soil 

  • Clay soil retains a lot of moisture and is very drought tolerant, therefore it will supply your plants with plenty of water during a dry season. 
  • Several plants thrive in clay soil such as birch and hawthorn trees, owing to their nutrient-rich and moisture-rich properties. 
  • Certain particles in clay soil bind to nutrients such as calcium, magnesium, and potassium that feed plants and improve their growth. 

Disadvantages of Clay Soil 

  • Clay soil has small spaces that trap water and do not allow moisture and air to move freely to the plant root systems, eventually killing the plants.
  • Clay soil is much heavier than other soils such as loamy soil, which makes it harder to break apart or till through. 
  • Clay soil is hard as a rock when it’s not waterlogged and heavy, making it difficult for seeds to sprout.
clay soil

Is Clay Soil Acidic or Alkaline? 

Getting to the big question is clay soil alkaline or acidic?

For the most part, clay soil is alkaline, which is often referred to as sweet soil, and has a pH above 7

Clay soil being alkaline is rich in sodium, calcium, and magnesium and is less soluble than acidic or neutral soil. This means that the availability of nutrients is often limited, resulting in stunted growth and nutrient deficiency in plants and flowers. 

There are several reasons for the alkalinity in clay soil, most notably watering with hard water that contains lime. In most cases, you will have to lower the alkaline level of clay soil in your yard and entire garden bed by making certain amendments. 

How to Lower Clay Soil pH? 

There are several amendments that you can make to lower the alkaline pH level of clay soil such as by adding:

  • Compost
  • Manure
  • Organic soil amendments like alfalfa meal

Vinegar has a variety of uses and can help lower the soil pH of clay soil, and best of all without the use of store-bought common fertilizers or organic matter. Simply spray vinegar on the soil to adjust the pH level of clay soil. 

Aluminum sulfate is another great way to amend clay soil pH and produces almost instant results as long as moisture is present. 

Iron sulfate is also an easy way to lower clay soil pH and make clay soil acidic or neutral but does require large quantities and takes as long as three to four weeks. 

Here is a detailed guide on gardening in clay soils.

adding compost to clay soil

Final Thoughts

Clay garden soil, for the most part, is alkaline but the good news is that there are several amendments you can make to lower the soil pH such as with animal-related organic matter and household products like vinegar. 

Most clay soils and alkaline soils are the hardest soil to work with and don’t provide good drainage but work wonders for some plants when it comes to gardening. However, it’s important to check the soil’s pH level before making any amendments.


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