Organic Soil
You can increase the amount of organic matter in your soil by adding compost, aged animal manures, green manures (cover crops), mulches or peat moss. Because most soil life and plant roots are located in the top 6 inches of soil, concentrate on this upper layer.
pH levels of 6.5 to 6.8, which is why most plants grow best in this range.
Acidic Soil. If the pH of your soil is less than 6.5, it may be too acidic for most garden plants (although some, such as blueberries and azaleas require acidic soil). Soils in the eastern half of the U.S. are usually on the acidic side.
The most common way to raise the pH of your soil (make it less acidic) is to add powdered limestone.
Wood ash will also raise the pH, and it works more quickly than limestone and contains potassium and trace elements.
For best results, apply wood ash in the winter, and apply no more than 2 pounds per 100 square feet, every two to three years.
To raise the pH of your soil by about one point:
In sandy soil: add 3 to 4 pounds of ground limestone per 100 square feet.
In loam (good garden soil): add 7 to 8 pounds per 100 square feet.
In heavy clay: add 8 to 10 pounds per 100 square feet.
Alkaline Soil. If your soil is higher than 6.8, you will need to acidify your soil. Soils in the western U.S., especially in arid regions, are typically alkaline. Soil is usually acidified by adding ground sulfur. You can also incorporate naturally acidic organic materials such as conifer needles, sawdust, peat moss and oak leaves.
To lower soil pH by about one point:
In sandy soil: add 1 pound ground sulphur per 100 square feet.
In loam (good garden soil): add 1.5 to 2 pounds per 100 square feet.
In heavy clay: add 2 pounds per 100 square feet.
Reference:
https://www.gardeners.com/how-to/building-healthy-soil/5060.html#:~:text=You%20can%20increase%20the%20amount,concentrate%20on%20this%20upper%20layer.
