Acid Loving Plants and Soil Modification

If you are trying to acidify your soil for growing acid loving plants such as blueberries and rhododendrons, it has been traditional to recommend adding either sulfur or acid–based organic material such as pine needles or oak leaves.
Recent research has shown that adding sulfur will drop pH over the course of a year, but that combining the sulfur and the organic material drops the pH much faster and much more.
Bottom line:
if you want to grow blueberries or other acid–loving plants, add both the sulfur and the organic matter for best results.
Suitable organic matter would include: ground-up lemons, pine needles, or oak leaves among other thing.
“Organic Amendments and Sulfur in Combination Reduce Soil pH,” Maren J. Mochizuki (University of California Exten- sion, Ventura, CA), A. James Downer, and Ben Faber.