Soil Analysis: What’s the Point?

The Importance of Soil Analysis for a Thriving Garden

Every gardener has probably read that a soil analysis is recommended for a successful garden. However, for reasons that are more or less explainable, few of us actually do it. How do you sample your garden? Where to take the soil sample?

Here are a few basic questions to which we suggest some answers.

We know that soil health is the foundation on which a fertile garden rests. Understanding the composition of our soil allows us to grow healthy, vigorous plants. But since no one has a laser beam in their eyes to determine the percentage of organic matter accurately, an analysis to better tame your garden can be useful.

How Do I Do a Soil Analysis?

To ensure that the sample is representative of your vegetable garden, you need to take 3 to 5 sub-samples from different locations, to a depth of 0 to 20 cm. Then mix them evenly before sending them to the laboratory. Avoid areas of heavy traffic, areas where water collects – in short, areas that don’t represent the garden as a whole.

There are two main types of soil analysis. Chemical analysis and physical analysis (granulometry). The former will reveal the levels of nutrients crucial to plant growth, such as phosphorus, potassium, calcium and magnesium, as well as lesser-known elements like boron, manganese, sulfur and copper. It can also be used to determine the soil’s pH and percentage of organic matter.

To put it simply, for most vegetable crops, a good pH is between 6.0 and 6.5, which allows nutrients to be absorbed by the roots. Outside this window, you run the risk of reducing nutrient availability and fertilizing… for nothing!

Nitrogen

Although nitrogen is the preferred plant nutrient, which is why it comes first in fertilizer formulations (the famous N-P-K), it will not be included in the results, as it is too mobile in the soil. In other words, its concentration will vary rapidly and it is not relevant to measure it. Fertilization in agriculture is based on this element, but according to the sampling of different vegetables and not according to analyses, unlike phosphorus and potassium. An analysis every 3 to 5 years is sufficient to check nutrient concentration.

Granulometric analysis is used to determine soil texture, which can be clayey, sandy or silty. There are 13 classes in all (Figure 1). To measure it, we need to determine the proportion of mineral particles that make up the soil, i.e. the percentage of sand, silt and clay. This analysis doesn’t need to be carried out several times, as soil texture is unlikely to change. Here in Quebec, its composition dates back to the last glaciation and then to the retreat of the Champlain Sea (unless a large quantity of sand or clay is imported). In other words, the province’s soils are around 10,000 years old.

In-house testing is possible

It’s also possible to perform a home-made test, the jar test. Or with a little, or a lot, of practice, it’s possible to perform a test by forming a ball of soil that you place in your hand and moisten lightly. The more you can form a long, thin ribbon, or make pottery with our soil, the more clay it contains. Conversely, if you form a ball with your sample and it bursts when you apply pressure between thumb and forefinger, it contains a lot of sand and little clay.

Soil texture influences water circulation and reserve, nutrient content and susceptibility to compaction. So it’s possible to adjust fertilization and watering frequency according to the soil you’re growing in, two key actions for a productive garden. Clays are richer in organic matter and therefore more nutritious than sands.

How Do I Get a Soil Analysis?

You can do business with an agricultural cooperative, some garden centers or directly with a laboratory.

Soil testing is a complementary tool for any gardener concerned about the health and prosperity of his or her garden. By understanding the unique characteristics of soil, it’s easier to make informed decisions that promote healthy plant growth. A second article explaining how to interpret the results will help you better understand your soil. You’ll then be able to capitalize on its strengths, while minimizing its weaknesses.