Almost all fruit requires a neutral or slightly acid soil, while figs and grapes bear a slight alkalinity.
Each plant therefore has special requirements in terms of pH. And it is therefore very important to be able to measure its value before planting a garden or using a substrate.
Knowledge of the pH level of the soil can also be useful in the treatment of certain diseases, such as potato scabies which tend to attack in soils with a high lime content.
Rain or irrigation water that circulates in the ground mixes with soil particles that we call mineral salts, present in the soil itself or added with fertilizers. Part of these salts is retained by the clays present in the soil (absorbing power), others dissolve in water (circulating solution) thus reaching the roots of the plants.
The pH of the soil depends on the amount of OH or H ions present in the circulating solution: with more OH ions the reaction is basic or alkaline, with more H ions it is acidic. If OH and H ions are equal, the reaction is neutral.
The ratio between OH and H ions is measured with a scale of values ranging from 0 to 14: the acidity goes from 0 to 6.9, the maximum is O and the minimum is 6.9; 7 indicates neutrality (ie the parity between OH and H ions); the alkalinity ranges from 7.1 to 14, the maximum is 14 and the minimum 7.1.
Strongly acidic soil pH 4
Acid medium pH 5
Moderately acidic soil pH 6
Neutral soil pH 7
Calcareous soil pH 8
Strongly calcareous soil pH 9
A medium with a pH higher than 7 is called alkaline. A soil with a pH lower than 6.5 is called acid. Soils with pH values above 8.5 or below 4.5 are rare.
Most of the most common garden plants are indifferent to the type of soil, but like soils with a reaction ranging from pH 6.5 to pH 7.2.
Regardless of this we have 3 categories:
· Those that tolerate or even prefer calcareous (or alkaline) soils;
· Those that do not tolerate calcareous soils and want acid soils;
· Those that thrive both in acid soils and in calcareous soils.
· Plants that do not tolerate calcareous soils can only grow in acid or neutral soils. The most important of these are the Rhododendrons, along with other plants such as the Azalea, the Kalmia, the Pieris, the Gaultheria, the Liquidambar, the Erica, the Camellia, the Andromeda, the Quercus Ilex, La Kalmia and Il Lupino .
· Plants that like calcareous soils give less good results in acid to neutral soils (for example roses).
· Many vegetables grow best in a slightly acid soil, with a pH of about 6.5; instead, cabbage, beans, onions and asparagus also grow in soils with a pH of 7.
PH control: pH measurement
Following an empirical evaluation, we will say that generally sandy soils tend to acidity, while clayey and calcareous ones tend to be alkaline.
Lack of lime determines the acidity of the soil.
If the soil is rich in lime it is called alkaline. If it lacks lime it is called acid.
To know the pH of your soil, you can send a sample of the soil to one of the specialized laboratories that offer this analysis service, but the products necessary to perform a rough check exist on the market.
Take small samples from different parts of the garden and immerse them in the solution supplied with the equipment. Allow the particles to settle, then compare the color of the liquid with the color scale included in the package. The pH value is indicated by the intensity of the color taken by the solution in the test tube.
The check should be regular, especially when trying to change an abnormal reaction.
One of the most effective instruments for measuring the acidity of the soil is the Harvest Piaccameter, which is the only meter for immediately reading soil pH: just introduce it into the soil and read the pH value on the dial.
Reactive papers are used only when it is sufficient to establish very roughly the pH of the soil and are particularly useful for guidance field tests.
It operates directly on the ground suspension by immersing the map soaked in indicator liquid, then compares the color assumed by the map with that of a specially printed colored staircase.
A type of map is uniformly soaked in various indicators, so as to record the change in color in the individual pH fields of the indicator. The assay approximation is about 0.2-0.3 pH.