The soil pH scale runs from 0-14. Most plants grow best in a soil pH of 6.0 to 6.8. There are always exceptions to that rule though, and your oaks and rhododendrons are two of them. They prefer a pH of 4.5 to 5.5.
Have you had your soil tested lately? Or ever? Good news, PHS Meadowbrook Farm now offers free soil pH testing services.
Here are quick and easy directions for taking a sample so that we can give you a timely and accurate result.
Dig down into the soil (below your mulch, if using) 4 to 6 inches in several different places in the area to be tested. If the soil all appears to be the same color and texture, take two tablespoons from each area. (Do not use a metal container to gather samples, use a bag.) Spread it out on a sheet of newspaper overnight to dry. Once dried, mix all the samples together in a plastic bag and bring it to us.
Depending on what you are trying to grow, we can tell you if you need to raise the pH by adding dolomitic limestone or lower the pH by adding sulfur. These products are available at PHS Meadowbrook Farm.