Soil pH is important because it influences which nutrients in the soil get absorbed by plants. It’s measured from 0.0 to 14.0, where 0.0 is most acidic (sour), 7.0 is neutral, and 14.0 is most alkaline (sweet).
For those of you like us who are curious to know what pH stands for, p refers to the mathematical operation “-log10” and H stands for the element hydrogen, and together they become this scientific formula pH = – log10[H+]. It’s a bit complicated to explain how the entire equation works but pH, in a sense, is a measure of the amount of hydrogen bonds present in a substance.
Soils that have a pH between 5.5 and 6.5 are generally the best for most plants. Soil bacteria are most active within this range so they help break down organic matter and release nitrogen into the soil for plants to absorb. Other nutrients and minerals such as phosphorus, sulphur, calcium, magnesium, and iron are also easily accessible in the soil within this range.
When soil pH falls below 5.0, nutrients begin leaching out of soil rapidly. It also increases the likelihood for aluminum to become toxic to plants, to the point that it can kill them.
In addition to influencing the availability of nutrients, soil pH also affects the composition of soil. Soils with clay that have a pH between 5.5 and 7.0 are loose and granular, making them easy to till. But if the pH in these soils becomes too alkaline or too acidic, they become sticky and hard.
To amend soils that have become too acidic or alkaline, farmers usually use lime or sulphur. Lime raises the pH and makes soil more alkaline (sweet) while sulphur lowers the pH and makes soil more acidic (sour). If you need to raise or lower your soil pH, it’s best to do it slowly over a year or two. Adding too much lime or sulphur in one go can push your soil pH to one extreme, which will make the situation worse. Instead of lime or sulphur, apply a layer of organic compost to your soil. Compost is a soil moderator so it will slowly make your soil reach a pH of 6.5, and will also add organic matter.