How To Know If You Have A Clay Soil

As a soil scientist I am all too familiar with the stresses associated with a clay soil. Clay soil is an issue for large scale farmers all the way to hobby gardeners. Clay soil left untouched can cause a number of issues ranging from erosion, water logged soil and suffocated roots. 

Clay soil is fixable through different methods ranging from physical manipulation, chemical or physical amendments, and even crop choices. In this blog post we will be looking at:

  • Where does clay soil come from
  • How to identify problem clay soil
  • Crops used to help reclaim clay soil 
  • Physical manipulation to fix clay soil 
  • Soil amendments that fix clay soil

Be sure to grab my garden soil testing book to help you test your soil and understand what type of soil you have. This was written and designed by a soil scientist. It’s fun for adults and children! It will also allow you to track your soil profile health year after year.

Where does clay soil come from?

Clay soil is found in areas that have a large depression. If you look at the landscape surrounding a clay soil you will notice that it is in a low spot. This is because clay soils are found in areas that used to be ancient lake beds. These ancient lake beds have very fine sediment that is deposited through gravity and settling over time. The initial sediments are a result of rapidly flowing rivers entering a lake bed. These rivers were turbulent and therefore they would break away at the bed rock and rock in its pathway. This fine inorganic material was eventually turned into the powder mixture we now call clay.

North America is covered by the old lake bed. Many of which were here during the last ice age. You can look at maps to see your city or town to see where they were located. And to identify if you were in an ancient lake bed area. The other case would be a recent lake that has either dried up or has receded. If you were living in an area of a receded lakebed then this will also cause high clay soils.

If you’re noticing that your garden or land mass is splotched with clay you may be in a glacial till area. Having a combination of sandy soil and clay soil is not uncommon in a glacial till landscape. Glacial till is simply a way to describe a landscape that has been torn up by glaciers. This tearing up of the soil surface and bedrock has resulted in areas of rock deposits, sand deposits, and even clay. These landscapes also typically have a wide range of both chemical and physical attributes.

How to identify problem clay soil?

Being able to identify a clay soil is important when determining how to reclaim it. A true clay soil is often rare. The more common clay version of soil we see is a sandy loam or a loam of some sort. If you have a loam soil then you are less likely to experience the intense negative side effects of a clay soil.  If you are unsure how to check  your soil texture at home then be sure to check out my work booklet that goes through exactly how to test your soil.

Signs You Have Clay Soil As Seen In Crops.

The first sign that you may have a heavy clay soil or a clay soil that needs reclamation is through crop performance. Some things you may notice in a crop grown in heavy clay soil is lack of performance. This may show up in a few different ways.

The first sign of this being a root rot or chlorosis scenario. Chlorosis is the development of yellow leaf margins and green leaf veins. This is a sign that your soil pH is not adequate for plant growth. This change in pH is commonly caused by lack of drainage which is commonly found in clay soils. The other sign you have a heavy clay soil would be root rot.

If a plant dies off and you are able to simply pluck from the ground with very little roots attached. This may be a sign that you have suffered from root rot. Root rot is another sign of poor draining soil in the garden. Poor draining soil is a sign of heavy clay particles due to lack of drainage and aeration.

You will need to use some common sense here. If you are dealing with a large amount of rainfall, overwatering or some form of flooding when the symptoms arise. This may not mean the soil is heavy clay but rather the weather conditions have caused the issue.

Water Pooling On The Soil Surface Is A Sign Of Clay Soil

The other sign that you may have a heavy clay soil is based on pooling. If you have pooling in your garden after a heavy rainfall that persists for hours this is a sign you may have clay soil. Because clay particles are so close together we run into issues of water pooling. The other way to test this water retention level is through a percolation test. I also outlined how to perform this test in your garden in my soil testing book.

Colours In Clay Soil

The colour of your soil or lack of colour in your soil is also another indication of clay material. Because Clay is able to retain water and has a poor ability for drainage, things such as oxidation of iron in the soil profile will cause a rusted look. That rusted appearance is a sign that the soil has a heavy clay content and is unable to drain in an acceptable time frame.

Surface Soil Erosion In Clay Soils

If there is signs of erosion on the surface this is another sign that you may have a clay soil. Because the water is not able to penetrate the soil profile quickly if the angle of the landscape is at all downhill then you  may have signs of erosion. These signs of erosion would include Gully’s or rills. These typically look like rivers when the water is flowing and similar to ditches when the water dries out.

At Home Soil Tests

One of my favourite test to perform in the field when deciding if you have a heavy clay soil is the ribbon test. When performing the ribbon test it does take some practice. Simply take some clay soil and make a ball from there try to make a ribbon and see what length you can get the ribbon to. If you are able to achieve a ribbon that is over 3 inches in length it is likely you have clay. The longer the ribbon the higher the clay content.

Crops Used To Help Reclaim Clay Soil 

The use of specific crops to reclaim clay soils is becoming a popular method. This is because it does not require a huge mechanical input and gives the plants the opportunity to fix the soil. Using tillage equipment on clay soil is not only expensive but hard on the machinery. The planting of specific crops for the purpose of reclaiming clay soil is not only less expensive but in some cases more effective.

Tap Root Crops To Help Improve Drainage In Clay Soils 

One crop that is becoming very popular for this process is the Daikon radish, also known as the tillage radish.The tillage radish has a taproot that can penetrate the soil to an appropriate depth.  The best penetration into the soil profile does two things, First it fractures the soil horizontally and secondly it fractures the soil vertically.

The Daikon radish  has the ability to penetrate soil that is compacted up to 300 PSI. This means that the root is able to break up the soil profile and allow for airflow. Once the tillage radish has fractured the soil and allowed for increased airflow and aggregation. Microbes and the life is brought back into the soil profile. This is due to the increased amounts of oxygen that help nourish aerobic microbes. Aerobic microbes are responsible for things such as nutrient cycling.

Anaerobic microbes which are found in soils that lack oxygen such as compacted clay soils  are known to be the cause of issues such as root rot. Anaerobic microbes are unable to survive in a soil profile that has aeration. A tillage radish is very similar to an aerator that is used on a lawn.

Cover Crop Such As Alfalfa For Clay Soils

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Cover cropping or intercropping with alfalfa. You don’t have to necessarily use alfalfa for this however because Alfalfa has a taproot it is beneficial when it comes to aggregation. Alfalfa is a perfect choice if you are looking to add some colour to your garden or soil profile while reaping the benefits of nitrogen fixation.

Alfalfa is a popular crop in the farming industry but I do see a future for it in backyard gardens. Alfalfa due to its taproot it is able to penetrate through heavy clay soils. This again is going to allow for aeration and also aggregation of the soil.

Physical Manipulation To Fix Clay Soil 

Physical manipulation of clay soil is generally a last attempt to reclaim the soil. This is because physical manipulation such as tillage will disrupt the natural aggregation of the soil. Once these aggregates are pounded into a fine dust you will actually end up with higher levels of compaction. Whereas if we are able to add specific crops to a clay soil to work off of the current aggregation we don’t run into this issue.

Drainage Channels To Reduce Erosion In Clay Soil

The first and probably most favorable is the addition of drainage channels. These drainage channels result in better flow of water in and on the landscape. These do not have to be complex and can simply be ditches or small canal’s cut into the soil surface in strategic areas. All leading to a reservoir or a catching pond.

On a more expensive level we can install things such as tile drainage to help reduce the water pooling and effects of runoff. Either way both methods will decrease the amount of erosion that we see after a heavy rainfall. This is important because it will not only conserve our topsoil but it will also potentially save seeds, seedlings and plants.

Hills & Terracing To Help Clay Soil Erosion 

The method of hills or terracing a clay soil has been around for decades. It is a commonly seen method of agriculture even in ancient societies. And this is because it does work. However the labour is intense leading up to its completion. The main objective is to cause the water or the flow of topsoil to stop at the end of each Terrace.

Overtime as the soil stabilizes with vegetation on top of it the runoff will no longer be an issue. This is because the plant or the organic biomass on the soil surface will actually retain the moisture. While in a gardening method this would work. It would need to be maintained and most likely rebuilt over time. This is simply because gravity does have an effect on soil that does not have vegetation or root biomass holding the plant soil in place.

Tillage & Clay Soils 

The use of tillage in a soil system has started to become a negative word. However in some cases it may be the only course of action. If you are strapped for time and cash this may be your only solution. There is nothing wrong with using tillage on a small scale or for a temporary period of time. This will allow you to garden in that area within the initial season  with less effect on the plant.

However if the soil is an incredibly heavy clay soil this may not work as planned. Because a heavy clay soil can pack and solidify so quickly you may need to take your time in finding a solution for your garden. In some cases if the soil is that heavy in clay it may be best to do a raised bed system.

Soil Amendments That Fix Clay Soil 

There are many forms of amendments you can add to clay soil to remediate them. Some of these include commercial products. However yo u can use simple things such as wood chips, rocks, pumice and any other material that will increase aeration. While these physical editions will temporarily relieve the issue you may still need to use some chemical methods.

Lime For Clay Soil Systems

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The addition of lime to a clay soil system that is acidic in nature will actually help adjust the Ph. This adjustment in the pH of the soil will result in an aggregation by causing the clay particles to form bonds. This bond forming process will help increase the level of aeration and ultimately allow for better root penetration and microbe activity. The best way to gauge how much lime should be applied is based on the product recommendation.

When applying lime it is best to rototill or mix it into the soil. Generally I would like to get the lime within the first 2 inches or more when possible. This is some labor-intensive work but the benefits are pretty great. After a lime application you can wait some time before doing a second application. For example it is not uncommon to add lime in the spring and then re-evaluate for adding more in the fall. 

Gypsum For Clay Soils

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The use of gypsum in clay soil is another edition similar to lime that claims to be able to change the soil PH. Therefore changing not only the chemistry but the physical properties of the soil profile. However there are some studies that have come out showing this may not be the case. If you choose to give it to use a gypsum product in the garden then be sure to follow the application instructions on the package. If you do not see results within the first year it is probably safe to say that gypsum in your soil system is unlikely to perform.

As a soil scientist this is one of the most common questions I receive. You are officially ready to understand exactly what it takes to fix a clay soil. Do not worry not all hope is lost when you have clay soil in the garden there are some fixes that can be applied. However if you are incredibly frustrated with your clay soil system it may not be a bad idea to Simply switch to raised beds. Be sure to check out the YouTube video that goes into a bit more detail about clay soil systems and don’t forget to grab the garden DIY Sol testing handbook. Let me know in the comments below if you’ve tested your swell and what the results came back as.