Why is the pH value so important?

The pH value influences how well plants can absorb the nutrients from the fertiliser. Even if you use high-quality fertilisers, your plants may show nutrient deficiencies if the pH value is not right. This is because the availability of nutrients is strongly dependent on the pH value.

How the pH value influences the availability of nutrients

Every plant needs essential nutrients such as nitrogen (N), phosphorus (P), potassium (K) and micronutrients such as iron, manganese and zinc. The pH value determines whether these nutrients are dissolved in the substrate and accessible to the roots:

• • Acidic pH (span, <.5): Many micronutrients such as iron and manganese are over-available, which can lead to toxicity. At the same time, macronutrients such as phosphorus are less easily absorbed.

• • Neutral to slightly acidic pH (5.5-7.0): Optimum availability of most nutrients. This range is ideal for most plants.

• • Alkaline pH (span, >7.5): Micronutrients such as iron and zinc are insufficiently absorbed, which can lead to deficiency symptoms such as chlorosis (yellow leaves).

Nutrient blockages with the wrong pH value

An unbalanced pH value can cause so-called nutrient blockages. Although the nutrients are present in the substrate, they are not available to the plant. For example:

• • Acidic soil: lack of calcium, magnesium and phosphorus.

• • Alkaline soil: lack of iron, copper and zinc.