Certain plants prefer different acidity levels. Blueberries, for instance, like acidic soil because iron and aluminum can be extracted easily from it. Pine needles around blueberry bushes are especially helpful for increased acidity!
With soil, pH is the most important number to remember. The acidity or alkalinity of soil is measured on a scale from 0 to 14. The higher the concentration of hydrogen ions in the soil solution, the lower the pH, or acidity. Seven, being the middle number, is neutral, and plants grow best between 6.0 to 7.5.
Rainy climates often have acidic soil because other nutrients like calcium, magnesium and potassium tend to get washed away, leaving hydrogen ions behind. In arid climates, the opposite is true; those important nutrients tend to dominate the top layers of the soil.
This is where compost is helpful! Compost buffers the acidity of soil by binding to soil nutrients until the plants need them. If compost doesn’t do it enough, to change the acidity of your soil, you can also add ground limestone to make it more basic or sulphur to make it more acidic. The change that these methods create tends to be temporary though, so it’s best to match the right plants with the right soil pH.