Soil Pt. 1: Ideal Soil Conditions

Today we’re going to talk about soil.  

Now, I know, this topic does not sound that exciting. The soil under our feet seems like the plainest thing in the world. But what many people don’t know is that there’s a lot more to it than meets the eye, and the fact is that the health of your soil is extremely important when it comes to the productivity of your garden plants and the nutrition content of the stuff you grow. So let’s dig in and find out what kind of soil conditions work best for gardening! 

Soil is a combination of three basic ingredients: sand, clay, and silt. These are different types of earth that are differentiated by the size of their grains. The soil in each place is composed of different percentages of sand, clay, and silt, which determines what type of soil it is (such as “sandy loam” or “silty clay”).  ​​

This chart is used to determine soil type based on the % of sand, silt, and clay. Image by Christopher Aragón (unmodified).

Each type of soil comes with its challenges for gardeners. Soil with a higher percentage of sand dries out quickly, while soil with a higher percentage of clay is extremely dense. The best type of soil for agriculture is loam, which is composed of equal parts sand and silt and a lower percentage of clay. Unfortunately, there are relatively few places with perfect loamy soil. Chances are, the soil in your area is either sandy soil or clay soil. 
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Topsoil (the layer of earth closest to the surface) contains a lot more than sand, clay, and silt particles, though; in fact, it constitutes an entire world that is largely invisible to the human eye.  Every cubic inch of it teems with complex networks of microorganisms such as bacteria and fungi, as well as larger organisms like earthworms, nematodes, and insects. In nature, plants and animals die and fall on the ground, and these organisms work to decompose them. They turn the organic material into humus, or decayed plant and animal matter. This cycle of decomposition allows nutrients that were once inside of living things to returned to the ground to be used again. 

Some of the life forms that live in soil. Image by USDA.

There are lots of different nutrients in soil, but some of the most important nutrients for growing vegetables are nitrogen, phosphorus, and potassium. Garden plants need access to these nutrients in order to grow. To get at these nutrients and to collect water, your plants need to be able to spread their roots through the soil. This is much easier for them if your soil is properly aerated, or light and fluffy instead of dense and compact. The organisms that live in your garden help to mix oxygen into the soil by digging and burrowing. Your soil also needs to have a good balance of proper drainage (water going down through the soil instead of getting stuck at the surface) and water retention (not drying out too quickly).  
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Furthermore, soil is either alkaline or acidic. How can you tell what kind the soil in your area is? One easy way is to buy a soil test from a gardening center. The test will measure the pH of your soil. Soil that is acidic will have a pH of less than 7, while soil that is alkaline will have a pH of more than 7. Knowing the pH of your soil is important because if your soil is extremely acidic or extremely alkaline, it will be difficult for your plants to grow. While some vegetables prefer slightly acidic soils and others prefer slightly alkaline soils, a good pH to aim for is between 6 and 7.5. ​

​To summarize, the ideal soil for gardening: 

• Contains lots of organisms like earthworms and nematodes, which make nutrients accessible and aerate the soil. 
• Has plenty of humus, or decomposed organic matter.  
• Contains nutrients like potassium, nitrogen, and phosphorus.  
• Has good drainage and water retention. 
• Is nicely aerated so plant roots can grow easily. 
• ​Has a pH between 6 and 7.5.

Sounds great, doesn’t it? If everyone had this type of soil, crop yields would be through the roof. Unfortunately, soil rarely possesses all these qualities. It’s either dry sandy soil or dense clay soil, is depleted of nutrients, and lacks organic matter.  
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We think of soil as tough. In reality, topsoil is delicate. Commercial agriculture, construction, mining, and other human activities all significantly disturb the soil in natural areas, which took millennia to form. Once the complex world of humus, nutrients, and microorganisms is destroyed, it can take decades, if not centuries, for topsoil to regenerate. Without healthy topsoil, people can’t grow food. (This is why soil conservation and regenerative agricultural practices are so important!) 

When you think about it, people wouldn't exist if topsoil didn't! Image by Lynda Richardson.

In the garden, we can take steps to actively improve the quality of our soil and to keep it in top shape. That's what we will learn about in our next post!

As always, if you have any questions or tips to share, please comment below! ​