Altering Your Soil pH

While the soil pH can be altered with the intentional addition of specific soil amendments (e.g., lime to increase pH), I often advise new gardeners to avoid doing this. Generally, an acidic soil has a pH lower than 5.5. While it is possible to lower soil pH, altering it can have a negative impact on other plants which are already in situ. Dramatically changing the pH may alter the bloom colour of certain plants, but can also harm others. If one’s goal is to enjoy beautiful blue macrophylla hydrangeas, it’s best to alter the pH within the safety of a container or pot. And, as always, one should be checking their soil health annually using a soil test. One should never add soil amendments until this critical step is performed. 

Instead of altering the soil pH, gardeners are often best to work with the soil conditions that naturally occur. There are hundreds of fantastic native plants to all regions of Ontario and they will perform well in the existing soil conditions. Most soil tests often come with a useful guide showing the wide variety of plants that will thrive at various pH levels. As a gardener becomes more experienced, they may choose to carefully attempt to alter the pH in a small section of the garden in order to grow particular plants that require such conditions. 

If one chooses to alter the pH of their garden soil, it is recommended to apply amendments slowly. In the case of raising the pH, the application of a lime-based amendment is best. Gardeners are advised to apply their soil amendments in either fall or spring and always follow the instructions on the product label. Lime amendments vary on their composition and application, so following instructions is critical for success. 

On the inverse, if one wishes to increase the soil pH, the application of sulfur would be the most prudent route. In either case, gardeners must consider the both the type/texture of the soil, as well as the soil’s existing pH, in order to determine the quantity of the respective amendment.