Sulfur to acidify soil
I think I may have been sold the wrong kind of sulfur? Our soil is pretty neutral, so we want to lower the ph around our grapes and blueberries. The guy at the farm store sold us wettable sulfur, but that is used as a pesticide. Can it also be used to lower the ph of soil? Or do I need to buy elemental sulfur? Thanks!
Blueberries like a pH of 4.5-5.5, while grapes prefer a neutral pH. Our native soil is slightly acidic, (4.8-6.2) averaging about 5.5. Elemental sulfur is probably the best way to lower pH in your soil. Wettable sulfur is used as a pesticide to control insects and diseases. Performing a soil pH test before you add sulfur is a good idea to determine the need to adjust it. You can measure the effects of adding sulfur by following up with a second pH test after adding it a month or so after adding sulfur. That way you don't take the pH down too far. Changing pH is a process and takes time. When mixed with soil, microorganisms in the soil metabolize the sulfur into sulfuric acid, which lowers pH. To work the sulfur must be worked into the soil. The best time to add sulfur is the fall. For established plants they recommend digging at least 4 holes a foot deep and 4-8 inches in diameter, then mixing 1/4 cup elemental sulfur with the soil from the hole and replace the soil in the hole. Water in well.
This article from OSU gives additional information on acidifying soil in our area, Acidifying Soil https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/ec1560.pdf.