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Improving the soil in your garden: why and how?

Soil amendments are supplementary products provided to the soil in order to improve its structure and composition in the long term, with the goal of making it suitable for the needs of the plants that will be grown there. Before looking in detail at the different possible amendments and how they differ from fertilizers, it is important to have a good understanding of the soil.

Analyzing the soil

It is important to bring the soil to the best possible state of fertility, meaning it is loose enough to allow for easy rooting at depth and well-aerated enough for excess rain to drain away but still able to retain, along with the fertilizers, the elements necessary to nourish the plants. The ideal garden soil is made up of 65% sand, 10% limestone, 5% humus, and is neutral (as opposed to acidic) with a pH of 6.5 to 7.

Nothing is visible to the naked eye except for the richness in earthworms, which is necessary. Only a soil analysis will prevent deficiencies and avoid excesses in terms of amendments. Therefore, a good balance between clay, which gives the soil consistency, and organic matter, which maintains the correct humus level and provides nutritional elements while retaining the necessary water, is needed.

Difference between amendments and fertilizers

There is often confusion between amendments and fertilizers. To clarify, fertilizers provide elements that are intended to nourish the plant for satisfactory growth (nitrogen, potassium, phosphorus, as well as trace elements such as magnesium, zinc, copper, calcium...). Fertilizers can be either chemical, meaning synthetic, or natural, either organic or mineral. However, fertilizers do not affect the structure of the soil, which is the main difference with amendments.

Amendments, on the other hand, modify the physical-chemical state of the soil and improve its structure. Amendments can be either mineral or organic.

Mineral amendments

Bentonitic clay

Bentonitic clay has an interesting water retention power and is able to mix well with humus: it is intended for sandy and limy soils that will dry out much less quickly. Incorporate in the fall or winter by raking: 1kg/m².


Basalt strengthens the constitution of sandy soils and makes heavy soils lighter. It enhances microbial life and resistance to diseases thanks to the minerals and trace elements it contains. Spread all year round: 500g to 1kg/m².


Dolomite is a limestone amendment intended for clay soils and/or those lacking in magnesium. It lightens the soil and helps with the decomposition of organic matter. Spread in the fall or winter: 1kg/m².

Organic amendments

Compost Compost improves the structure of the soil and provides humus. Make your own by composting household and garden waste, or buy it from a producer. Spread in the fall or winter: 20cm to 30cm, worked into the top 30cm of soil.


Manure provides nutritional elements and improves the structure of the soil. Choose a mature manure (at least 6 months old) to avoid burning the plants. Spread in the fall or winter: 20cm to 30cm, worked into the top 30cm of soil.

It is important to choose amendments according to the needs of your soil and plants. It is also advisable to respect the recommended doses and incorporate them into the soil evenly. Finally, it is recommended to do a soil analysis before using amendments in order to determine any deficiencies or excesses in nutritional elements and target the necessary actions.


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