Module 3: Understanding Soil

For beginner gardeners, soil can be a daunting subject to approach. Understanding the basics of different types of soil and its components is critical to creating a successful and healthy garden. As part of our beginner’s gardening course, we will discuss the fundamentals of soil, from identifying different types to pH levels and how to improve your garden’s soil quality.

Soil is the foundation of any garden, and it is essential to know the basics of it to grow healthy and beautiful plants.

So, what is soil? Simply put, it is a mixture of organic and inorganic materials that provide the nutrients necessary for plants to grow. It is a complex system comprising minerals, water, air, organic matter, and living organisms.

Key terms

Most people understand the concept of soil, but when it comes to gardening, there’s a lot more to know about what lies beneath than just dirt. We will explain the difference between these types of soil and what organic matter and compost are so that you can better understand your garden’s needs.

Soil

Organic matter, minerals, gases, liquids, and organisms that support life are all found in soil. Some scientific definitions distinguish dirt from soil by limiting the former to displaced soil.

It provides the necessary nutrients for plant growth. Typically found on the ground’s surface, it can vary significantly in composition depending on the location and the types of plants that grow in it. It can be sandy, clayey, or loamy, and each type has different properties that affect how well plants grow.

Mud

Mud is a mixture of water, soil, loam, silt, or clay. Most of the time, it forms after rain or near water sources. Ancient mud deposits harden into sedimentary rocks like mudstone and shale throughout geological time. It is often found near bodies of water or in areas that have recently experienced heavy rainfall.

Mud can be challenging to work with, and it’s not a suitable material for planting because it lacks the necessary structure and nutrients to support plant growth.

Soil and mud are two different materials commonly found in gardens, and novice gardeners need to understand their differences.

Mud is a mixture of soil and water, which creates a wet and sticky substance. It is often found near bodies of water or in areas that have recently experienced heavy rainfall. Mud can be challenging to work with, and it’s not a suitable material for planting because it lacks the necessary structure and nutrients to support plant growth.

Is mud the same thing as soil?

Soil is a mixture of organic and inorganic materials that provide the necessary nutrients for plant growth. It is typically found on the ground’s surface and can vary significantly in composition depending on the location and the types of plants that grow in it. Soil can be sandy, clayey, or loamy, and each type has different properties that affect how well plants grow.

Humus or Organic

Soil humus comprises the natural matter or humus that falls on the dirt. A soil layer has formed due to the organic material’s breakdown. The size of the segment can vary depending on this layer.

Topsoil

As its name suggests, topsoil is the earth’s uppermost layer, usually the first two to eight inches. It forms over many years as rocks break down and mix with leaves, bugs, and dead animals. It can take more than a century to develop. So, topsoil has a lot of natural nutrients and minerals that help plants grow, like nitrogen, potassium, magnesium, phosphorus, and so on. The soil will appear darker the more organic matter it contains.

Subsoil

The subsoil is the layer below the topsoil that is typically rockier and sandier and does not usually contain as much organic matter. That said, the topsoil layer provides your plants with the appropriate amount of water and nutrients.

Compost

Compost is a mixture of ingredients used as plant fertiliser to improve soil’s physical, chemical, and biological properties. It is commonly prepared by decomposing plant and food waste, recycled organic materials, and manure.

Ericaceous

Ericaceous compost is a type with a higher acidity that gets its name from the “Ericaceae” family of plants that like to grow there. For these plants to flourish, a more acidic compost is necessary. Some ericaceous plants include Rhododendrons, Azaleas, Camellias and Heathers.

Organic matter

Organic matter is used for organic matter in the soil, and many manures, composts and other organic materials are added to the ground to increase the organic matter content. All organic matter derives from living things, mainly plants and animal origin. Some materials are best rotted or composted before use for a favourable carbon: nitrogen ratio. Examples of organic matter are animal manure, fallen leaves, garden compost, kitchen waste, lawn mowing and leafmould.

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Soil Types

You can choose the right plants for your garden and keep them healthy by knowing the type of soil you have—clay, sand, silt, loam, peat, or chalk.

Clay

Over 25% of clay soils contain clay. Because they have nutrients bound to the clay minerals in the ground, these, also known as heavy soils, may be fertile. However, they also hold a significant amount of water due to the capillary attraction of the tiny spaces between the numerous clay particles. They drain slowly and take longer to warm up in the spring than sandy soils do. When wet, clay soils are easy to compact and frequently crack clearly when they bake hard in the summer. This dirt frequently puts the landscaper through their paces, but it can be extremely rewarding when managed correctly with plant selection and development.

Clay soils are fertile and nutrient-rich if the organic matter can break down their cloudiness. The clay is broken up into smaller pieces by this, making it easier for plant roots to get to the clay’s water and nutrients. Breaking the clay into crumbs also warms the soil, makes it easier to work with, and reduces the likelihood of compacting it.

Sand

There is a lot of sand and little earth in sandy soils. These soils, also known as light soils, drain quickly after rain or watering and are simple to cultivate and work with. In the spring, they warm up faster than clay soils do. But they dry out quickly and lack plant nutrients, which rain quickly washes away. The acidity of sandy soils is frequently high.

These light soils typically lack nutrients and quickly lose water, especially those that drain freely. You can increase your soil’s capacity to hold water and nutrients by adding a lot of organic matter to bind the loose sand into more fertile crumbs. Fertilisers may also be required for plants grown in sandy soils.

Silt

Silt soils, mostly made of particles of intermediate size, are fertile, moderately well-drained, and retain more moisture than sandy soils, but they are also easy to compact.

These soils have fine particles that are easily compacted with garden equipment and trowels. They are susceptible to wind erosion and washing away if plants do not cover them. However, they tend to be quite fertile because they hold more water and contain more nutrients than sandy soils. The silt can be transformed into more stable crumbs by binding it with organic matter.

Loams

Loams are composed of a mixture of clay, sand, and silt, avoiding the extremes of sandy or clay soils. They are easy to work, have good drainage, and are fertile. Depending on their predominant composition and cultivation characteristics, they can be sandy-loam or clay-loam.

These soils are a gardener’s best friend because they contain all soil particle types’ “perfect” balance. However, despite their excellent quality, if you dig or cultivate these soils annually, it is essential to add organic matter regularly.

Chalky or lime-rich

Soils that are chalky or have a lot of lime, which can be light or heavy, are mostly made of calcium carbonate and are very alkaline. Consequently, they cannot support ericaceous plants, which thrive in acidic conditions. In extremely chalky soils, lumps of white chalky stone may be visible. Plants that can thrive in alkaline environments are preferable because these soils cannot be acidified. Despite variations, many chalky soils are shallow, free-draining, and low in fertility. However, nutrient levels and water-holding capacity may be higher in areas with clay.

How to identify your soil type and texture

1. Soil texture can be determined by taking a small amount of soil and rolling it between your fingers.
   • If it feels gritty, it may be sandy.
   • If it feels sticky, it may be clay.
   • If it feels smooth and crumbly, it may be loam.
2. Check the soil’s colour.
   • Dark brown or black soil is usually high in organic matter
   • Lighter soil colour indicates a lower organic matter content.
3. Test the soil’s drainage.
   • Dig a hole 30cm x 30cm
   • Fill the hole with water and let it drain completely.
   • Fill the hole again and measure the depth of the water
   • Measure the depth of the water every two to three hours. The water level of well-draining soil will drop at least an inch each hour.
4. Dig a hole about 6 inches deep and fill it with water.
   • If the water drains quickly, the soil may be sandy.
   • If the water drains slowly, the soil may be clay.
   • If the water drains moderately, the soil may be loam.
5. Test the soil’s pH. Use a pH testing kit to determine the soil’s acidity or alkalinity. Most plants prefer a pH between 6.0 and 7.5.
6. Check for organic matter content. A high organic matter content can improve soil structure, nutrient retention, and water-holding capacity.
7. Observe plant growth. Different plants grow better in different soil types. If certain plants are thriving in your garden, it may indicate the type of soil you have.
8. Look for the presence of rocks and gravel. Sandy soil may contain more rocks and gravel than clay or loam soils.
9. Check for the presence of earthworms. Earthworms can help improve soil structure and nutrient cycling.

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Soil pH

Before designing and planting your garden, you will need to know the pH of the soil because different plants thrive in different soils. A pH is a number that shows how acidic or alkaline it is. At 7.0, the pH is considered neutral. Acid soil has a pH below 7.0, whereas alkaline soil has a pH above 7.0.

Testing soil pH

Chemistry plays a role here; fortunately, it’s easy to understand. The pH scale is used to determine the soil’s acidity and alkalinity. The “potential of hydrogen” is called the “pH” value. On the full scale, which ranges from 1 to 14, most garden soils fall within the range of 3.5 to 8.5.

Testing should be possible year-round; however, if lime, compost or natural matter has been added in the last 90 days, the outcomes may be misleading.

How to identify the pH of your soil.

1. Dig a small hole in the soil about 4 inches deep using a trowel or a shovel.
2. Take a small amount of soil from the bottom of the hole and put it into a clean container.
3. Repeat steps 3 and 4 in several locations where you want to test.
4. Mix the soil samples in the container.
5. Remove any stones, twigs, or other debris from the soil.
6. Put a small amount of the mixed soil sample into a soil test kit tube.
7. Add the barium sulfate powder to the tube according to the instructions.
8. Add distilled water to the tube, filling it to the mark indicated on it.
9. Shake the tube vigorously for 30 seconds.
10. Allow the tube to sit for 5-10 minutes until the soil settles.
11. Observe the colour of the soil in the tube.
12. Compare the colour to the colour chart in the instructions for the soil test kit.
13. Record the soil’s pH level and repeat steps 8-14 for each soil sample taken from different locations in the garden.

Pro tip: Choose a day for testing when the soil is dry for the most accurate results. Avoid testing after rain or watering.

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How to improve your soil

If you feel your soil conditions are not up to standard, you can plant in containers or improve your soil conditions.

By digging and forking your way through the soil, you can loosen any compaction, remove weeds and other debris, and add organic matter.

Plants need great soil conditions assuming they are to give the best outcomes. Working on the dirt with a lot of organic matter in the form of compost helps waste and air circulation on heavy soils and monitors fundamental dampness on light ones.

1. Thoroughly dig the soil, breaking up large lumps to relieve compaction. Using a spade for soil that has never been dug will be easier.
2. Add a 5cm layer of organic matter (homemade garden compost, bagged compost or well-rotted manure) over the surface before digging or forking it into the soil. These organic fertilisers are more beneficial to soil bacteria than inorganic compounds.
3. Dig over the soil to incorporate the organic matter. Mix into the soil to the depth of the spade or fork tines.
4. Tread over the area, using your heels to firm the soil. If there are any large lumps, break them up with the back for a fork.
5. Finish by raking over the soil to remove stones or rouge weed seedlings. This makes an even layer for planting or sowing.

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Coming Next

That’s it for today. Hopefully, you have more of an understanding of the different soil types and how to test soil types and pH. You may need to refer back to this information in the future, so why not download our Understanding Soil pdf to keep for the future.

The next stage of our course is Module 4 – Introduction to Garden Design pt1.

Further Reading

Soil Types: A Beginners Guide

Soil Types: Understanding pH & Testing Soils

Soil Types: Acidifying Soils