Step by step: analyze the soil pH

Step by step: analyze the soil pH

Are you starting a garden and wondering if this or that plant will please you? Or have you been gardening for years, always disappointing when you try to introduce such a variety? Be aware that a simple pH test can help you make the right culture choices and avoid unnecessary and costly failures. Indeed, some plants will only like themselves in a soil of a given type and will perish if the conditions offered are all different. This is the case for example of rhododendron which requires an acid soil (pHgenêt or the poppy will need an alkaline soil (pH> 7) to flourish. What are we talking about when we talk about pH (or Hydrogen potential)? pH is the unit of measurement for the presence of hydrogen ions in the soil, which is linked to the very nature of the soil. We measure this presence by a chemical test which will reveal the acidity , the neutrality or the basicity of the soil, the values ​​ranging from 1 to 14, from the most acid to the most alkaline, the neutrality being around 7. This rate varies not only according to the soil composition , but also what it receives (rain, amendments, etc.). It has a direct impact on the assimilation of nutrients by the plant, and on the microbial life of the soil, whose role is to transform organic matter into humus.


The different pH testers The pH meter Consisting of a probe and a screen for reading the measurement, it is the most reliable means of measuring the acidity of a soil. After introducing the probe into the ground, it measures the potential difference between two electrodes located in the probe, then converts the measurement to a pH unit. However, it is a bit expensive and for a one-off need, a hundred euros may seem prohibitive. The pH indicator paper Less precise, it is made up of strips impregnated with colored indicators which will reveal themselves according to the acidity of the soil. A chromatic scale is provided on paper, allowing the color of the strip to be compared. The pH test measuring the lime content There is a palliative which consists in determining the lime content of the soil. This content is directly linked to the acidity of the soil. For this we use a reagent which will react to the presence of lime by coloring. This is the test we used. The test of red cabbage The leaves of red cabbage contain dyes (anthocyanins) which have the distinction of changing color depending on the acidity of the medium. This substance is used by some commercial color indicators. You will find pages on the Web explaining how to make your own indicator using red cabbage leaves ...

Step 1: Take the samples

Using a transplanter, take 4 small samples from different places where you are used to sowing or planting your flowers or vegetables. Samples are taken from soil of the same physiognomy and having previously received the same treatment, preferably after harvest or flowering. It will be necessary to make a separate analysis for specific environments such as embankments, rock gardens, ditches, ponds ... It is necessary to take the earth to a depth between 5cm and 20cm, or more simply, the depth to which the roots of your plants are used to getting their nutrients. If the soil is too sticky or too soggy, take your samples the day before and let them dry overnight in the shelter.

Step 2: Mix the samples

What interests us is to obtain a global statement of the acidity of the soil in our garden. To do this, mix the samples well together, as a very small part will be used for analysis. Take the opportunity to remove stones and other unwanted residue.

Step 3: Analyze the samples

Follow the instructions to perform the analysis. Here, it is recommended to introduce 10mm of soil in a glass tube.
Fill the tube with distilled water (usually provided). Failing this, it is possible to use demineralized water, but the results could be distorted since they have been specifically established to use distilled water (pure water) made according to a different process.
Introduce the reagent. In the case which concerns us, it is a simple pellet. Shake it for a long time before it dissolves completely in the solution.
Shake the contents and let sit until the solution clears and the deposits fall to the bottom of the tube.
Compare the color obtained with that of the chromatic table which is provided to identify the acidity of your soil.

Step 4: Interpret the results

Rich in this teaching, you are free to intervene or not on the soil of your garden. Knowledge of the acidity of the soil and its composition will tell you about its fertility. Plant needs: - Acidiphilic plants need a pH between 4.5 and 5.5 - The majority of plants evolve in an environment where the pH is between 5.5 and 6.5 - Basiphilic (alkaline) plants need a pH between 6.5 and 7.5 If you do not intervene, knowing the pH of your soil will allow you to adapt your crops to your soil type. Potatoes, for example, are less prone to disease in an acidic environment (pH 5.5). Hydrangeas opt for the color blue in an acid medium (pH below 6) and pink in a neutral medium (pH between 6 and 7), as such, they are a good natural indicator of pH. If you decide to intervene, do not rush the ground, and a correction range of one point is to be considered as a maximum. - In the case of an acid soil, less than 5, an addition of lime or magnesium may reduce this acidity and stimulate the recomposition of the soil, but you will also need to add organic matter by adding potting soil, compost … These amendments are generally made during wintering. - In the case of a soil that is too basic, greater than 8, you can correct it by adding humus or peat, thereby lowering the pH.