All about the land of our gardens

All about the land of our gardens

The topsoil - that is to say the cultivable part of the soil - of our gardens comes mainly from the disintegration of rocks and the decomposition of organic matter. Various observations over very long periods, several hundred years, show that it forms at the rate of one millimeter every six years on average. We can easily understand the precious nature of this thin layer of soil that allows our plants and vegetables to grow. The earth is a living element which is constantly changing, especially under the effect of cultures. For this reason, care must be taken to ensure that the various elements that constitute it remain as long as possible in adequate proportions for the type of culture that you wish to develop there.

What is the earth made of?

Let's first talk about the texture of the earth. It is determined by the main physical elements that compose it, namely sand, clay, limestone and humus. On their respective proportions in the soil will depend the behavior of the ground: powdery, compact, stony, sticky. There are different ways of correcting the texture of a soil at the level of a small garden, by adding - as needed - river sand, blond peat, clay. Ideal garden soil is loose soil that works well and works well, thus favoring the production of humus. A sensory analysis can be enough to identify the type of a soil, there are several kinds: sausage technique, jar, taste, knife, washing ... you will find many on the Internet, sometimes clever and fun. Let us dwell for a moment on the humus which is the main element of the topsoil. It is he who feeds the plants, promotes the biological activity of the soil and strengthens its structure. Land without humus is dead land. Humus comes from the natural decomposition of organic materials such as plant residues, roots of dead plants, stems and dead leaves, but also from manure, peat, compost, potting soil. This decomposition is due to oxygen, but is greatly accelerated by the presence of microorganisms that populate the soil - bacteria, fungi - which work tirelessly to transform organic matter. It is the humus that will nourish the plants by providing them with the necessary nutrients. It also has a structuring role in soils. A very old saying says that "humus gives body to light soils and softens compact soils". By improving the soil by adding organic matter, its characteristics are also modified, so that a clay soil will become more permeable, and that a sandy soil will increase its water retention capacity. The soil is also characterized by an acidity level (pH) and by the presence of many chemical elements. It is always good to know the pH of the soil in your garden, because some plants will refuse to grow in an acid medium (low pH), and others in an alkaline medium (high pH). If you only want to know the pH of your soil, you will find inexpensive and ready-to-use color kits in garden centers. If you want to know everything about your land, the analysis is done in the laboratory on the basis of samples: it is an expensive solution (around 80 euros), but which gives detailed results, precious when you begins a vegetable patch.
Here are some of the elements that will be measured in the case of a laboratory analysis: - pH : it determines how nutrients behave in the soil. We will choose plants adapted to the pH of the soil in which they will be grown. Some plants appreciate an acidic environment (heather and rhododendrons for example), others only grow in alkaline soil (marigolds and bellflowers for example). In the case which concerns us, garden and vegetable garden, the soil pH must be neutral or basic (pH = 7), even slightly acidic (6.5 Nitrogen (N): it is the basic element which benefits the aerial part of plants: stems and foliage. Phosphorus (P) : this element strengthens the resistance of plants and contributes to the development of roots. - Potassium (K) : this element contributes to flowering and fruit development. In garden centers you will find so-called NPK fertilizers with varying dosages. For example, a NPK 9-14-19 fertilizer corresponds to a dosage of 9% of Nitrogen (N), 14% of Phosphorus (P) and 19% of Potassium (K): it is the typical combination of a fertilizer for roses. Other elements are also sought, such as calcium, magnesium, the percentage of organic matter ... Note that these analyzes must be commented to allow you to make any necessary corrections.

How to recognize the different types of soil?

Without resorting to laboratory analysis, here are some clues that will allow you to have a first idea of ​​the type of soil in your garden. Know that plants growing spontaneously on your land are a good indicator of soil acidity: they are called "bio indicator" plants. If there is no ideal soil, a good compromise - for a soil that is easy to work, draining and slightly acid suitable for growing in our gardens and vegetable gardens - could be a soil composed respectively of 65% sand, 15% clay, 10% limestone and 10% humus. We often talk about "free" land. Organic indicator plants: white chickweed, lanceolate plantain, spotted alfalfa, buttercup, sorrel… We are talking about a clay soil when sticky when wet. Slightly damp, it sticks to tools and sticks under your soles. This same earth will be very hard during the summer, forming cracks on its surface, and if it starts to rain, the water will stagnate there. Clay soils are rather acidic, but sometimes alkaline. Organic indicator plants: bindweed, crocus, mint, daisy, buttercup, pelus spurge ... Possible improvements: drainage, lightening of the soil (peat, sand) and amendment of organic matter (compost, manure, etc.). Liming is possible without excess. Conversely, a sandy soil or siliceous will have no outfit, it will crumble even when wet. We recognize the sandy soil with its high permeability, swallowing water and requiring short and frequent watering in summer. It is a very airy soil, which allows it to be less subject to sudden temperature variations in winter and summer. Siliceous earths generally have a fairly neutral pH, but can be acidic or alkaline. Organic indicator plants: heather, broom, purslane, sisymbre wisdom, horsetail, sorrel, 4 seed vetch… Possible improvements: significant inputs of organic matter (compost, manure, mulch, etc.), clay, and green manures.
A limestone earth can be recognized by its clear and milky color as well as by the numerous stones that compose it. It works quite well under normal conditions, but becomes sticky when wet. It is a soil that absorbs water well and retains it well. Limestone soil is never acidic. Organic indicator plants: marigold, slender spurge, hawkweed picris, common thistle, bellflower, wild mustard, yellow reseda, swollen moth, spring cinquefoil, bulbous buttercup ... Possible improvements: amendments (heather earth, manure, blond peat) and especially green manures (mustard, clover, white lupine, vetch ...). The humus earth has a dark brownish color. It absorbs water well and keeps it well, too often at the risk of being soggy. In summer, it tends to dry out quickly. It does not keep up well, but remains easy to work. Its fertility makes it very close to the famous soil that you know well. They are very often acidic soils. Organic indicator plants: heather, fern, broom, moss, mushroom, lanceolate plantain, poppy ... Possible improvements: supply of clay-limestone type topsoil or liming if necessary to reduce the acidity, drainage, fertilizers, but limited in nitrogen. It is not uncommon to encounter these four types of soil in a composite manner. Indeed, we have more often to do with clay-limestone, silico-clay, sandy-silty, clay-silty, silty soils…
Earth is a chemically extremely complex medium in which reactions of all kinds take place, constantly changing its composition and acidity. One of the roles of the gardener will be to take care to maintain a healthy balance between all these components for the good health of his plants.