The vegetation is stopped, the winter is the ideal season to work on the soil of his garden, and attempt to remedy the difficulties, more or less recurring, experienced in previous years. This may be, the excessive proliferation of certain herbs say bad, cultures that “make evil” in the garden, or shrubs or flower beds that are languishing in spite of the good care that you bring them. Be aware that the origin of these evils can take on two letters: pH, or “potential of hydrogen”. In other words, a lack or, conversely, an excess of acidity of your soil.

The assimilation of minerals (nitrogen, phosphorus, potassium, magnesium, trace elements) that feed on the plants is directly conditioned by the amount of hydrogen ions (H +) present in your field. Some plants, called acid-loving, such as the rhododendron, the heath or the camellia, which have significant needs in acidity, so by H + ions (which are protons), while others are virtually allergic to them (high bush, dogwood).

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But it is extreme cases. To give the full measure of his potential, a soil of the garden should, in fact, be slightly acid to neutral, with a pH of between 6 and 7 (1 to 7 the medium is acid, 7 to 14 is basic or alkaline), as it is in this range that the nutrients are better absorbed by most plants, and that the risk of deficiency or exposure to certain parasites is minimized.

thus, a soil that is too basic has the effect of blocking the assimilation of iron in plants sensitive to chlorosis (yellowing of leaves), such as certain roses, the strawberry or the hydrangea. Or facilitate the emergence of certain pathogenic bacteria like the one that causes scab of the potato. Similarly, a soil that is too acidic can result in damage to crops such as garlic, onion, celery, and especially the cabbage, which, below a pH of 6.5, become susceptible to a fungus, parasite, hernia ( Plasmodiophora brassicae ).

How to measure the pH

The easiest method and the most economical is, in a first time, to observe the wild flora of your garden, because some plants are good indicators. The presence of daisy ( Bellis perennis ) of which the delicate carpet of white flowers light up your lawn in the spring, but also buttercup creeping ( Renonculus repens ), or sorrel-wild – ( Rumex acetosela ) means that your soil is acid.

others, on the contrary, as the scarlet pimpernel ( Anagallis arvensis ), the cornflower ( Centaurea jacea ) or wild buckwheat ( Polygonum convolvulus ), not to be confused with the buckwheat, are the sign of a basic medium. The geology between of course online account: soils developed from parent rock shale, or granitic (Brittany, Vendée, Massif central, etc.) are dominant acid, while the land located on a limestone subsoil (Champagne, Paris Basin, the Causses…) are mainly basic.

Vinegar and baking soda The presence of daisies means that your soil is acid. Tauralbus under a CC license

To validate this rapid diagnosis, collect several samples of earth from different points of your garden, mix it in a container and pour the white vinegar. If small bubbles of carbon dioxide gas (CO2) released from the solution, this means that your soil contains limestone and is therefore alkaline. If nothing happens, draw a second mixture in which you can add, this time, the baking soda dissolved in water. If a release of CO2 occurs, it means that your ground is acid. Finally, if your soil does not react to vinegar or to baking, you can conclude that it is neutral.

Now, if you want to know more precisely the value of your pH, in particular with a view to correct it, you can use strips of pH paper, impregnated colored indicators, that is easy to find in the trade.

The means to address

acid soil , it is recommended to apply because of their richness in calcium, the ash from your fireplace or your wood stove. You can also stir in at the end of the winter of maerl or lithothamme, crushed limestone, slag, potassium (if you can find one…) or the hydrated lime formula Ca (OH)2. Strictly follow the doses indicated in order not to change sharply the balance of your soil. The lower the pH (and therefore high acidity), and the correction must be accomplished by stages in the spread if necessary over several years. Then, the contributions of maintenance to maintain the pH at the desired level. Note that in the clay soil, the decrease of the acidity will make it less sticky and therefore easier to work with.

To turn blue, hydrangeas need to acidity and aluminum. 81951095/aquaphoto – stock.adobe.com

soil basic , the regular intake of peat (preferable to the land of the heather of the trade to the often poor quality), in sufficient quantity, is essential. This is particularly the case if you want to plant a rose garden or enjoy the best strawberries in the spring. Do also spray, or a watering of iron chelate to avoid chlorosis. If you want to grow plants very acidophilic (pH 4.5 to 5.5) as the camellia, azalea or rhododendron, you will need to downright take away the land of origin, to be replaced by a mixture of peat, earth, neutral and sand, non-calcareous. Unless you live in the Landes or in the Sologne region, where land, type podzolique, are naturally very acidic. Finally, to turn blue hydrangeas and hydrangéas, you just need to lower the pH below 6 by incorporating in the soil of the slate rocks or of aluminum salts. But the easiest way is probably to live in Britain or on the plateaus of the Limousin!

• This article is an updated version of that published on 17 January 2014.

Your appointment “garden” to do (mostly) not to be missed

• 26-27 January: feast of plants “Mimosalia”, on the theme of the”intelligence tree”, medieval village, Bormes-les-Mimosas (Var)

• 9 to 17 February: exhibition and sale of orchids, Vacherot & Lecoufle, floral Park of la Source, Orléans (Loiret).

• 14 February to 11 march: 7th exhibition “a Thousand and one orchids’, a large greenhouse of the Jardin des Plantes, Paris.

• 16 February: Conference “Gardening au natural: solutions exist”, espace Jean Vautrin, Bègles (Gironde).

• Until 28 February: exhibition “winter Gardens”, the Domain of Chaumont-sur-Loire (Loir-et-Cher).

• 28 February-3 march: Exhibitions “Pool & garden” et “My house, my desires”, Parc Chanot, Marseille (Bouches-du-Rhône).

• 2 to 4 march: 560e frequently asked trees and plants, Lisieux (Calvados).

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