Living in the Detroit metro area means our soil pH balance is alkaline. Evergreens and some flowering ornamentals, like azaleas, rhododendrons and dogwoods, to name a few, like an acid pH. A free soil test through the Michigan State University Extension office (instructions can be found at http://msusoiltest.com/get-your-soil-test/ ) can tell you exactly what your garden pH is, and if it needs correction. Should your soil sample come back as alkaline pH, the natural product that can help you change the balance from alkaline to acid is ferrous sulfate. At A Southern Gardener, we apply ferrous sulfate once a month from April through October, one cup worked into the soil around the base of each plant, more if it is a tree or large shrub. Ferrous sulfate can be found at your local garden center, is a natural product and an inexpensive soil supplement. Keep in mind, though, this is a process that can take a few years to achieve the acid balance your plants need. You will know how the pH has changed by taking another soil test in a couple years.
You need to know your garden soil in order to have garden success!