Creating well-aerated soil is a crucial aspect of gardening, but aerating some dirt can be challenging due to small soil pore sizes. If you’re unfamiliar with soil pores, you might wonder what they are and how they impact soil quality. Fortunately, this article can help!
Soil pores are the small spaces between particles of dirt. Every soil type has distinct soil pore sizes. These pores are crucial to soil drainage and aeration, impacting plant growth and root health. To create soil pores, you can till and amend the soil, helping your garden thrive.
This article will explain soil pores and discuss why they’re so important. You can use this information to create high-quality garden beds for plants.
What Are Soil Pores?
Have you ever spilled water on a baking sheet or tile floor? If so, you’ve likely noticed that the water pooled. That’s because the material it’s sitting on doesn’t allow the water to drain away.
Now think about what happens when you water a potted plant. In most cases, you’ve likely noticed that the water drains through the potting soil, leaving the surface damp but not flooded. That’s because well-aerated garden soil is rich in soil pores!
Soil pores are small gaps or bubbles of space between particles of soil. These pores allow water and air to pass through dirt, helping reduce surface flooding and increasing oxygen levels in the ground.
However, potting and garden soil is very different from natural soils, particularly those found in coastal areas, deserts, and bogs. These varying soils feature different pore sizes, significantly impacting their ability to drain and trap oxygen.
Soil Type Affects Natural Pore Size
Pore size varies depending on soil type, as every soil is made of various natural components. These components typically include sand, clay, and humus (decayed organic matter).
The sand, clay, and humus proportions in any given soil sample significantly impact pore size. Let’s briefly examine the soil pores of these common soil types to understand their differences.
Sand Soil Pore Size
Most sand is composed of microscopic quartz caused by centuries and millennia of coastal erosion. Sand particles don’t adhere together readily, so sandy soil tends to be full of pores.
For this reason, water tends to drain through sandy soil rather quickly. This fast-draining quality can be beneficial for plants that prefer dry environments (like cacti) but detrimental for common garden plants like vegetables and flowers.
Clay Soil Pore Size
Clay soil is almost the opposite of sandy soil. It’s composed of silica and microscopic metals, many of which are attracted to one another.
This attraction results in a dense, sticky substance with few pores. Unlike sand, clay soil tends to retain (and sometimes repel) water, as its pores are exceptionally tiny and few.
Loam Soil Pore Size
Loam soil is composed of sand and clay. It’s also rich in humus, which is decayed organic matter (rotten leaves, decayed sticks, decomposed animals). This combination of elements ensures that loamy soils enjoy optimal soil pore size for plant growth.
The sand component in loam soil allows water to drain efficiently and helps trap oxygen beneath the soil surface. But the clay and humus components retain moisture and add stability to the soil, preventing rapid dehydration and providing life-sustaining nutrients to plants.
In other words:
- Sand consists of numerous macropores and micropores
- Clay consists of few micropores
- Loam consists of moderate macropores
Macropores vs. Micropores
Soil pores are divided into two categories based on their size.
The highest-quality garden soils contain plentiful macropores (gaps in soil greater than 0.03 inches or 0.08 mm). Conversely, exceptionally dense soils (like clay soil) tend to have much smaller pores, called micropores (gaps in soil smaller than 0.03 inches or 0.08 mm).
Gardeners will want to facilitate the creation of macropores in soil, as larger pore size is crucial to several aspects of healthy plant growth.
Why Are Soil Pores Important?
Soil pores are important because they are extremely vital to plant growth and overall health. The pores impact the following elements:
- Soil drainage
- Soil aeration
- Microorganisms in the soil
Let’s explore why these effects are essential to building a thriving garden.
Soil Pores Affect Soil Drainage
One of the primary reasons soil pores are essential is because they affect drainage. Soils that don’t contain many pores (or only consist of micropores) drain slowly, which can be problematic for plants that prefer quick-draining soils.
Soil that remains moist for extended periods also increases the risk of root rot, which can lead to plant death. Alternatively, soil rich in pores may drain too quickly, making it almost impossible for roots to absorb water and nutrients. This issue can also lead to premature plant death.
Soil Pores Provide Ventilation to Roots
In addition to impacting water movement, soil pores also affect soil ventilation.
A fantastic way to understand this principle is to imagine a large glass tank filled with sand. If you were to enter this tank and submerge yourself under the sand, breathing would be impossible.
However, if you filled the tank with plastic balls (like those found in child-friendly ball playpens), you’d be far less likely to suffocate. That’s because the space between the plastic balls is greater than the space between the grains of sand. This space provides room for oxygen.
Soil pores work in the same way, providing oxygen to plant roots. Though plants don’t have lungs like humans, they need oxygen to “breathe” via cellular respiration. All parts of a plant (leaves, stem, roots) are part of this respiration process.
Consequently, when a plant’s roots cannot take in dissolved oxygen in the soil via soil pores, the plant can struggle to survive, even in environments with high levels of airborne oxygen.
Soil Pores Impact Soil Microorganisms
While most gardeners loathe the idea of soil-borne microorganisms living in their garden beds, several terrestrial microorganisms are crucial to plant and soil health. These microbes and microscopic creatures consume and excrete decaying matter.
Some of these organisms convert airborne elements into usable nutrients that plants require to thrive!
A great example of this is Bacterium radicicola, a strain of bacteria found in soil. This microorganism can convert nitrogen in the air into bioavailable nitrogen that plants can use.
This might not seem significantly beneficial, but it’s crucial to remember that nitrogen is one of the most vital nutrients plants need to grow. Without it, most fruit-bearing plants, vegetables, and flowering plants would be unable to thrive.
However, dense soils with few pores can make it challenging for beneficial microorganisms to survive and reproduce. Soil lacking in pores can also become anaerobic, meaning it cannot retain oxygen.
This can prove particularly problematic for beneficial insects and worms in the soil. Earthworms are an excellent example. These tiny creatures naturally aerate the soil as they travel beneath the ground, but they need access to oxygen to survive.
How To Create Soil Pores
You can increase soil porosity via two primary methods:
- Tilling, and
- Soil amendation
If your outdoor or indoor plants are struggling to survive or grow, you’ll want to consider the soil’s pore size and (based on your findings) take action to increase pore size.
Till the Soil Before Planting
Whether you’re planting outdoors or indoors, it’s crucial to till the soil before planting.
This process adds oxygen to the dirt, ensuring that plant roots can access plenty of air. It also keeps soil from compacting, improving drainage and reducing the risk of root rot.
If you’re pouring potting soil out of a bag and into a container, the soil may naturally form large pores as it falls into the container. As such, tilling may not be necessary.
However, if you’re placing a plant into a pre-existing container full of soil, you’ll want to use a spade to aerate the soil before transferring the plant into the container.
Simply push the spade into the soil, and lift it. Be sure you’re transferring the dirt from the bottom of the container toward the top. The final result should be a loose mixture you can easily run your hands through.
A pole cultivator is the better tool to use if you’re working in an outdoor space.
Amend Soil To Create Larger Pores
If you’re not working with loamy soil, tilling may not be enough to ensure the soil is rich in pores. In this instance, it’s best to amend the soil type and texture before tilling.
The best way to amend soil varies depending on the native soil you’re working with. That said, most native soils can be made more porous and fertile with the help of garden soil and compost.
Depending on the area you intend to use for plants, you may need to purchase a significant amount (several cubic feet) of garden soil and natural fertilizer. Fortunately, you can use a helpful soil calculator to determine the amount of dirt you’ll need to fill your garden bed.
After adding garden soil and fertilizer (preferably organic options like manure), you’ll want to mix them using a shovel or cultivator. This last step helps add oxygen to the dirt and ensures an even mix of the loamy soil and nutrient-rich fertilizer.
Final Thoughts
Soil pores are small gaps of space between particles of soil. These openings allow water and air to pass through to the ground. They’re particularly crucial to plant health, as roots need access to water and oxygen to grow and remain healthy.
Though every soil type has different pore sizes, gardeners can improve the quality and size of soil pores by tilling the soil before planting. Amending soil types with tiny pores is also an excellent way to ensure that your garden soil drains appropriately and enjoys a boost of oxygenation.
If you want to learn more about improving soil quality, you can read my other article here: How To Improve Soil Quality (The Ultimate Guide)
