Soil Porosity

Photo by Jonathan Kemper

We all hope to create the optimal environment for our gardens but what does that mean?
It all starts with the health of the soil. Which is the combination of nutrients, texture, and porosity. These components will determine the soil’s ability to hold and regulate water and nutrients. Soil is a mixture of sand, silt and organic matter that supports plant growth.
Soil can have a variation of texture due to its solid particles. The three main physical textures are clay, loamy or sandy. Clay easy packs together and has fine particles. Loam is loose and will crumble while sandy soil will feel rough between your fingers due to the larger particles. 

The size of the soil particles will affect the level of porosity within the soil. Porosity is the pore space or small voids between the solid particles that contain either water or air. These pores or voids can be due to movement of worms, roots, expanding gases and soil additives.

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There are two main categories of soil porosity: micropores and macropores. These categories are based of the pore size or spaces. Depending on the size we can predict the levels of oxygen, nutrients, and the ability to retain water. The optimal porosity for plant growth is a ratio of both micro and macro-pores.

• Micro pores are smaller in size but are not affected by gravity and can retain water and nutrients longer. Due to the smaller pore size the movement of air and water is sometimes restricted making it difficult for the roots to extract both the nutrients and water. Clay soils have a greater ratio of micro-pores.
• Macro pores are a large pore size which allows air and water movement enabling optimal oxygen for root growth. The larger pore size also creates an environment for gravity to decrease the nutrients more quickly. Sandy textured soils, have a greater ratio of macro-pores.​ 

Understanding the role that porosity plays in creating healthy soil will impact what we add to our garden soil. Porosity is vital for optimal growth. The plants will degrade and die without a combination of both micro and macro pores. Leaving the ground dry and depleted of nutrients or waterlogged and stagnant. Assisting the porosity of the soil can be as easy as mixing in organic material such as wool pellets, worms, and planting annual lettuces into your gardens. 
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Photo by Wild Valley Farms

Photo by Jonathan Kemper

Photo by Erda Estremera

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Wool pellets expand as they absorb water creating a space. That not only increase oxygen but holds the nutrients in the soil for root development. As they begin to biodegrade that space is replaced by air, increasing soil oxygen levels.

Introducing worms to the soil will increase the porosity of the top inches of your soil. As they create deeper tunnels in the soil it will also help with drainage preventing root rot.
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Consider adding lettuce that can be harvested at ground level and the root system left. Once harvested the roots will die off leaving spaces for water, oxygen, and other nutrients to fill their space.

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