High pH levels in soils can slow the growth of mycorrhizae colonies. Most mycorrhizae prefer soils with low pH levels. However, studies have found that plants and fungi can change the pH levels in the soil when they work together.
When planting trees, flowers or shrubs that prefer acid soils, it is often a good idea to add sulfur or another acidifying compound to the soil. This temporarily lowers the pH level and allows the mycorrhizae to flourish. Once the fungi have set up their colonies inside the plant roots, they start improving the soil. Mycorrhizae help acidify the soil, which is beneficial for them and their host plants.