• Naomi Stephens | Permaculture Designer

What's the best PH of soil for plants? Why is this important?

Updated: Apr 26

We all know how important soil is for the growth of plants. Soil supplies plants with the nutrients they need to grow. One of the many things that affect the growth of plants is the pH level of the soil.

What is the pH scale?

A pH is a measure that specifies how acidic or alkaline a substance is. It runs from 0 to 14.

The 0 to 6.9 range is acidic and 7.1 to 14 range is alkaline.

A value of exactly 7 on the pH scale is considered to be neutral.

Why is the pH of soil important?

Too much of anything is bad and the same goes for the pH range. An extremely low or high pH level is not good for the growth of plants.

The availability of nutrients in the soil is affected by pH level of the soil. If the soil is too acidic or too alkaline, it can cause a reduction in the availability of certain nutrients.

How does the pH affect the nutrient uptake?

Certain nutrients like manganese, phosphorus, and aluminum are found in slightly alkaline soil.

Manganese is a vital nutrient required in a plant, especially for the process of photosynthesis.

Phosphorus is an essential nutrient for the growth of a plant as it is involved in many vital functions of a plant. For example, phosphorus is needed in photosynthesis, transfer of energy throughout the plant, starch and sugar transformation.

Aluminium promotes the uptake of nutrients and increases the tolerance of a plant against abiotic stress.

Acidic soil can cause all these nutrients to become noxious, which can affect plant growth.

There are other nutrients such as copper, iron, and zinc, which are also fundamental for plants and are found in slightly acidic soil.

Copper helps in forming lignin in a cell wall. It also acts as a catalyst in the respiration and photosynthesis procedures of a plant.

Iron is an important element required to maintain the structure and function of a chloroplast in a plant cell. It is also essential for respiration and photosynthesis.

Zinc is responsible for the production of chlorophyll in plants. The deficiency of zinc in the soil can cause chlorosis in plants, discoloration of the leaf.

If the soil happens to be highly alkaline, it can cause a reduction in the availability of these nutrients, which, in turn, harms plant growth.

See the graph below for the optimum pH level for nutrients:

How do I amend the soil if it's too alkaline or acidic?

Acidic soil can be adjusted using lime to raise the pH level.

Alkaline soil can be amended using aluminum sulfate or elemental sulfur to lower the pH level.

What is the best pH level of soil?

Most essential nutrients are available in abundance in the soil of pH 7.

The only exception in this is manganese is more abundant in acidic levels of the soil.

To ensure that the soil has a sufficient amount of all the required elements, the best pH level is 6.5.

All the necessary elements such as iron, zinc, manganese, phosphorus, copper, boron, calcium, potassium, etc. are highly available at a pH level of 6.5.

You should carry out a soil test every 4-5 years. This helps in certifying that the pH level of the soil is at 6.5 so that plants can get the sufficient amount of nutrients they require for their growth.

You can test your soil using a soil ph tester kit. >

Or have a look below at other methods to test your soil:

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