Soil testing

Soil testing is an essential component of regenerative gardening practice as it allows for soil properties and characteristics to be identified.

The identification of soil properties such as depth, texture, structure, pH, cation exchange capacity and aggregate stability ensures successful management, plant selection and application of treatment solutions.

Most of the important soil properties can be identified with a simple do-it-yourself testing kit that can be purchased from the local garden centre. Other properties such as cation exchange capacity require in-depth lab analysis, this complex information is more relevant for larger growing operations such as agricultural projects, primary producers or flower farms.

This Soil Testing segment will aim to focus on information that is applicable to the home gardener, information that can be obtained with a simple testing kit.

The following is an example of a home testing kit. Remember to follow all safety procedures as specified in the instructions of each kit.

Soil pH:

Testing soil pH will allow you to determine whether the soil is alkaline, neutral or acidic. The pH of the soil can greatly impact nutrient availability. By determining the pH level, adjustments can be made to ensure the soil pH is within the appropriate range for the intended plants. The correct soil pH will promote healthy growth and nutrient uptake.

Soil pH directly influences nutrient availability to plants. Different nutrients have optimal availability at different pH ranges. For example, phosphorus tends to be less available in alkaline soils, while iron and zinc may be less available in highly acidic soils. By understanding the pH preferences of different plants and adjusting soil pH accordingly, you can ensure that essential nutrients are available for your plants.

Soil testing kits can be obtained from your local garden centre and are easy to use. Ensure you follow the safety instructions and the “how to” sections as they appear on each specific testing kit.

Below is a graph displaying nutrient availability according to the soil pH range. Thinner parts of the bars refers to a decrease in nutrient availability.

Soil Texture:

Soil testing provides information about the composition and texture of the soil. It helps to identify the proportions of sand, silt and clay. These proportions influence soil structure and drainage capabilities. With knowledge of soil texture, you will be able to correctly chose plants that suit the specific environment within your garden. Discovery of texture will allow for more efficient irrigation and fertilisation methods.

To work out the texture of your soil:

Step 1. Take a small sample of soil, a size that fits comfortably in the palm of one hand. Discard any gravel or large rocks.

Step 2. Moisten the soil with water, little by little, and knead until there is no apparent change in feel. This could take up to several minutes. 

Step 3. Squeeze the sample hard to see whether it will form a ball or sausage shape. And if so, whether the shape is durable or falls apart readily.

Step 4. Finally, squeeze it out between your thumb and forefinger with a sliding motion and note the length of the ribbon that is formed. 

Refer to the table below to identify soil texture.

The following video is an excellent example of how to perform the soil texture assessment.

Soil structure:

Soil structure is the term used to describe the way soil particles are arranged together. The mineral particles and humus are grouped together into crumbs or aggregates. These are arranged together so that there are spaces called pores between them. This arrangement give soil its characteristic structure.

A visual examination is all that is necessary to determine soil structure. Take a small sample of soil from the testing area and examine it closely. Consider the size, shape and arrangement of these particles. Common soil structures include granular, blocky, platy and crumb structures.

A soil has good structure if:

-       The particles that make up each aggregate are bound together firmly enough so that the aggregates do not break apart when rain falls on them or during normal digging.

-       The particles of each aggregate are still held together loosely enough so that small roots can penetrate aggregates to get water and nutrients.

-       The aggregates are generally quite small – ideally 0.2 to 3 mm across – rather than large clods that are dense.

-       The aggregates are arranged together in such a way that there are many pores (spaces and channels) between them.

Soil is a dynamic environment, a home for countless forms of living matter, competing and reacting with each other. For healthy plant growth, we must provide an environment of generous air spaces, prompt drainage of excess water and manageable levels of organic matter. These factors encourage and support aerobic organisms that are usually the helpers in garden soil. This situation allows easy penetration of root systems and promotes plant health and vigour.  

Regenerate your soil:

With this information you should be able to conduct a soil test at your own home. This information is your best friend when it comes to plant selection. When we understand what we are working with, we can begin to implement sustainable garden practices. These garden practices will promote reduced irrigation requirements, increased biological activity, reduced chemical input and thus overall garden health.  

Now you know what you are working with, refer to the “How to treat your soil” page to gain valuable knowledge and tips to help you foster an impeccable growing environment. If you want to learn more about Compost and organic matter refer to the “What is compost” page.